Appendix:Dictionary of Mining, Mineral, and Related Terms/T/2

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a. The property of the particles or molecules of a substance to resist separation; tensile strength.

b. The force of strength with which the particles (or molecules) of a mineral or rock hold together or resist separation. The terms commonly used to describe the tenacity of a mineral are friable, brittle, sectile, malleable, flexible, elastic, and tough.


a. Said of roof shale that tends to break up or crush under pressure into small fragments and that will not hold in any span over a few inches. Also called short.

b. The formal offer by the tenderer to carry out the work described in the drawings and/or specification for a certain sum of money. See also: agreement.


An isometric mineral, (Cu,Fe) (sub 12) As (sub 4) S (sub 13) ; tetrahedrite group; forms a series with tetrahedrite; may contain zinc, silver, or cobalt replacing copper; in veins; an important source of copper. Syn: gray copper ore.


A projecting tongue fitting into a corresponding cavity called a mortise.


See: grade.


A monoclinic mineral, CuO ; occurs in gray scales, black powder, or earthy masses; sp gr, 6.4; in oxidized zones of copper deposits; a source of copper. Syn: melaconite; black copper. See also: black copper ore.

tensile force

A force such as the force applied when a haulage rope pulls a set of tubs.

tensile strength

The maximum applied tensile stress that a body can withstand before failure occurs. Syn: tenacity. See also: ultimate tensile stress.

tensile stress

A normal stress that tends to cause separation across the plane on which it acts. CF: compressive stress.

tensile test

A test in which material is subjected to an increasing tensile pull until it fractures. A stress-strain curve may be plotted, and the limit of proportionality, proof stress, yield point, ultimate tensile stress, elongation, and reduction in area can be determined.


a. In subsidence, the amount of lengthening per unit of measurement.

b. In engineering, a pulling force or stress; metals in tension are strong, while concrete and masonry are weak. c. A system of forces tending to draw apart the parts of a body, esp. of a belt, a line, a cord, or a sheet, combined with an equal and opposite system of resisting forces of cohesion holding the parts of the body together. The stress caused by pulling; opposite of compression and distinguished from torsion. d. Sometimes used in place of voltage or electromotive force. See also: tension zone.

tension carriage

A bogie or frame carrying a pulley around which the rope of an endless rope haulage passes to be tensioned or tightened. The bogie moves on rails and may be kept taut by balance weights or placed on an inclined roadway (with sufficient weights) to move up or down according to the tension in the endless rope. A tension device is necessary to take up any slack rope created by varying loads on the haulage system.

tension-control cylinder

A hydraulic piston and cylinder mechanism that can be attached to a rotary-drill feedoff line and adjusted to allow the drill stem to feed downward while maintaining a constant preset tension on the drill string. See also: tension drilling.

tension correction

The correction that must be applied to a tape if it is being used at a tension different from that at which it was standardized. See also: tape corrections.

tension drilling

Drilling with part of the weight of the drill string supported by the drill swivel head or suspended on a drilling line, as opposed to drilling with the entire weight of the string imposed on the bit. See also: tension-control cylinder; weight indicator.

tension end

The tail end or receiving end of a belt conveyor. It consists of a return drum carried in a boxlike structure. A scraper, plow, or brush is attached to remove as much as possible of the spillage on the bottom belt before it passes on to the return drum. The tension end is drawn back by two sylvesters attached to staking anchor props; this enables adequate, but not excessive, tension to be imparted to the belt. See also: sylvester; tailend.

tension fault

a. A generic term for any fault caused by tension.

b. Geological fault due to tension, which separates rock strata; unlike gravity or normal fault, since strata may reappear on other side of gap caused by fall of intervening section to lower level when fissure opened.

tension flange

The side of a beam in tension, being the lower side in the general case of a simple beam supported at both ends.

tension fracture

a. A fracture that is the result of tensional stress in a rock. CF: shear fracture. See also: extension fracture; tension joint.

b. A fracture that is the result of stresses that tend to pull material apart. c. See: subsidiary fracture.

tension jack

A type of jack equipped with a jackscrew for wedging against the roof, which also has a ratchet device for applying tension on a chain to be attached to the tail or foot section of a belt conveyor. The jacks and tension chains pull the tail section back until the belt is at the proper tension.

tension joint

A joint that is a tension fracture. Syn: cross joint; tension fracture.

tension linkage

A chain application in which linear motion is not continuous in direction.

tension zone

The surface area affected by tensile strain. CF: compression zone; neutral zone; tension.

tepee butte

A conical hill or knoll resembling a Native American tepee; esp. an isolated, residual hill formed by a capping of resistant rock that protects the underlying softer material from erosion. Also spelled: teepee butte.


a. An evaporite consisting of a calcareous crust coating solid rocks on or just beneath the surface of an arid or semiarid region; a deposit of caliche.

b. Mex. A volcanic tuff, or a secondary volcanic or chemical nonmarine deposit, very commonly calcareous. Etymol. Mexican Sp., from Nahuatl (Aztec) tepetatl, stone matting.


A general term for all pyroclastics of a volcano.


A group of extrusive rocks, of basaltic character, primarily composed of calcic plagioclase, augite, and nepheline or leucite as the main feldspathoids, with accessory alkali feldspar; also, any member of that group; the extrusive equivalent of theralite. With the addition of olivine, the rock would be called a basanite.


Said of a rock resembling tephrite.


A coal-tar pitch, for protecting the outside of steel tubes against corrosion and bacteria.


A monoclinic mineral, Hg (sub 2) ClO ; yellow; at Terlingua, TX.

terminal curvature

A sharp, local change in the dip of strata or cleavage near a fault. Not commonly used in the United States. CF: drag.

terminal velocity

The constant velocity acquired by a particle falling in water or air when the frictional resistance is equal to the gravitational pull. See also: equal-falling particles; Stokes' law.


In mineralogy, the end of a crystal, esp. crystal faces that intercept the crystallographic axis, as distinguished from a broken or polished end. Crystals are singly terminated if faces appear on one end as in attached crystals or ones lacking the symmetry to require faces on both ends to complete a crystal form; they are doubly terminated if faces appear on both ends.

terms of reference

Schedule that defines responsibilities and area of activity delegated to and/or accepted by subsection, department, or subordinate official in organization working on line-and-staff system of large company where harmonious cooperation might otherwise be endangered.


a. A phase system that may be defined in terms of three components.

b. Any phase in a ternary system consisting of all three components. c. A eutectic, peritectic, or other singular point in a ternary system.

ternary steel

An alloy steel that contains one alloying element; the term is synonymous with a simple alloy steel. It contains the one element plus the iron and carbon, hence ternary.


Sheet iron or steel coated with an alloy of about four parts lead to one part tin.


Sheet steel covered with a tin-lead alloy.

Terni furnace

A modification of the open-hearth furnace in which the essential feature is the port design. The air ports gradually increase in cross section until they are as large as the hearth itself, thus practically eliminating turbulent flow in the furnace.


See: fichtelite.


Hydrocarbon present (30% to 60%) in pine oil, which is widely used as frother in the flotation process.


The principal frothing agent in pine oil.

terra alba

a. Finely pulverized powder, CaSO (sub 4) .2H (sub 2) O , made from gypsum and used in the manufacture of paper, paints, artificial marble, and composition plastics.

b. Any of several white mineral substances, such as (1) gypsum ground for a pigment; (2) kaolin used esp. as an adulterant of paints; (3) burnt alum; (4) magnesia; and (5) blanc fixe.


a. A level or nearly level plain, generally narrow in comparison with its length, from which the surface slopes upward on one side and downward on the other side. Terraces and their bounding slopes are formed in a variety of ways, some being aggradational and others degradational.

b. A flaw in marble, commonly cored out and filled up. c. A raised portion of an ancient riverbed or a bank on which alluvial deposits may be found. d. A bench in quarry or opencast mining. e. A ridge, a ridge and hollow, or a flat bench built along a ground contour. f. A narrow, gently sloping constructional coastal strip extending seaward or lakeward, and veneered by a sedimentary deposit; esp. a wave-built terrace. g. Loosely, a stripped wave-cut platform that has been exposed by uplift or by lowering of the water level; an elevated wave-cut bench. h. Any long, narrow, relatively level or gently inclined surface, generally less broad than a plain, bounded along one edge by a steeper descending slope and along the other by a steeper ascending slope; a large bench or steplike ledge breaking the continuity of a slope. The term is usually applied to both the lower or front slope (the riser) and the flattish surface (the tread), and it commonly denotes a valley-contained, aggradational form composed of unconsolidated material as contrasted with a bench eroded in solid rock. A terrace commonly occurs along the margin and above the level of a body of water, marking a former water level; e.g., a stream terrace. i. A term commonly but incorrectly applied to the deposit underlying the tread and riser of a terrace, esp. the alluvium of a stream terrace; this deposit should more properly be referred to as a fill, alluvial fill, or alluvial deposit, in order to differentiate it from the topographic form. j. See: structural terrace.

terrace placer

See: bench placer.

terra cotta clay

A term applied loosely to any fine-textured, fairly plastic clay that acquires a natural vitreous skin in burning and that is used in the manufacture of terra cotta. It is characterized by low shrinkage, freedom from warping, strong bonding, and absence of soluble salts.

terra-cotta model maker

One who makes metal profiles and wooden forms for use in casting plaster terra-cotta block mold.


A tract or region of the Earth's surface considered as a physical feature, an ecologic environment, or a site of some planned human activity, e.g., an engineering location; or in terms of military science, as in terrain analysis. Not to be confused with terrane.

terrain coefficient

A terrain coefficient is a number expressing the ratio of actual ground displacement by elastic waves to that which the same waves would produce in rock. The terrain coefficient for rock is thus 1; for unconsolidated materials it ranges upward to as high as 30, depending on the thickness of the material.

terrain correction

A correction applied to observed values obtained in geophysical surveys in order to remove the effect of variations in the observations due to the topography near observation sites. Syn: topographic correction.

terrain slope

Used to describe quarries when located in low slopes. CF: hillside.


a. A group of strata, a zone, or a series of rocks; used in the description of rocks in a general, provisional, or noncommittal sense.

b. A region considered in relation to its fitness for some purpose; an extent of ground or territory. c. A fault-bounded body of rock of regional extent, characterized by a geologic history different from that of contiguous terranes. A terrane is generally considered to be a discrete allochthonous fragment of oceanic or continental material added to a craton at an active margin by accretion. See also: suspect terrane. d. Informally, a region where a particular rock or group of rocks predominates. Not to be confused with terrain.

terra ponderosa

Literally, heavy earth; another name for heavy spar or barite.

terra rossa

A reddish-brown residual soil found as a mantle over limestone bedrock, typically in the karst areas around the Adriatic Sea, under conditions of Mediterranean-type climate. Also spelled: terra rosa. Etymol: Italian, red earth.


In marble working, a defective or disfigured place in a marble block, which is cut out and filled with a composition. Also spelled terrace.

terra sienna

See: ocher.

terra silicea

See: infusorial earth.


Small chips or pieces of stone, usually marble or limestone, about 1/2 to 3/4 in (1.3 to 1.9 cm) in diameter, made by crushing and screening. Terrazzo chips are used with portland cement in making floors, which are smoothed down and polished after the cement has hardened.


a. Pertaining to the Earth.

b. Pertaining to the Earth's dry land.

terrestrial deposit

a. A sedimentary deposit laid down on land above tidal reach, as opposed to a marine deposit, and including sediments resulting from the activity of glaciers, wind, rainwash, or streams; e.g., a lake deposit, or a continental deposit.

b. Strictly, a sedimentary deposit laid down on land, as opposed to one resulting from the action of water; e.g., a glacial or eolian deposit. c. A sedimentary deposit formed by springs or by underground water in rock cavities. CF: terrigenous deposit.

terrestrial magnetism

The natural magnetic field within and surrounding the Earth and the factors affecting it.

terre verte

a. Fr. "green earth". Glauconite or other phyllosilicate used as artist's pigment.

b. Collective name for various pale bluish-green earths formed by the disintegration of minerals, principally those of the hornblende type. Also called green earth.


Derived from the land or continent.

terrigenous deposit

Shallow marine sediment consisting of material eroded from the land surface. CF: terrestrial deposit.

terrigenous sediments

Sediments derived from the destruction of preexisting rocks on the Earth's surface, as distinguished, e.g., from sediments of organic or volcanic origin.


A plastic explosive that consists of the constituents blasting gelatin+BNT+sodium nitrate+ammonium perchlorate. The explosive has a relatively low rate of detonation and is very insensitive, on which account care must be taken to ensure that its initiation is extremely powerful.

territorial sea

A belt of sea, not exceeding 12 nmi (22.2 km) in breadth, lying beyond its land territory and internal waters and, in the case of an archipelagic State, its archipelagic waters, in which a coastal State has sovereignty.


An extra-strong high explosive of the nitroglycerin type.


The first period of the Cenozoic Era (after the Cretaceous of the Mesozoic Era and before the Quaternary), thought to have covered the span of time between 65 million years and 3 to 2 million years ago. It is divided into five epochs: the Paleocene, Eocene, Oligocene, Miocene, and Pliocene. It was originally designated an era rather than a period; in this sense, it may be considered to have either five periods (Paleocene, Eocene, Oligocene, Miocene, Pliocene) or two (Paleogene and Neogene), with the Pleistocene and Holocene included in the Neogene.

tertiary crushing

The preliminary breaking down of run-of-mine ore and sometimes coal. In metal mines, the tertiary crushing may be performed at a central point underground. See also: primary breaker.

tertiary grinding

When a particularly fine grinding of ore is needed, two and even three ball mills may be used in a series to attain the degree of fineness. The successive stages are referred to as primary, secondary, and tertiary grinding.

tertiary shaft

The shaft that extends a mine downward from the bottom of the secondary shaft.


Having three different valences. Syn: trivalent.


a. A surface divided into squares, or figures approaching squares, by joints or natural divisions.

b. Composed of tesserae--small cubes of stone, marble, glass, or terra cotta variously colored and arranged in artistic design: inlaid; mosaic; as tessellated pavement.


In crystallography, the same as isometric.


a. To search for mineral deposits in an unproved area by means of boreholes.

b. To obtain samples of soil or rock from which the physical characteristics of the soil or rock can be determined, such as in foundation testing. c. An exploratory borehole.

test bore

Drilling to test subsoil and rocks when considering foundations of buildings, dams, and heavy plant.

test boring

As used by foundation engineers, the act or process of sinking holes into the overburden (sometimes to considerable depth into bedrock) with rotary or drive sampling equipment for the purpose of recovering samples from which information on the physical characteristics of the materials penetrated can be obtained; also applied to the sample or samples so obtained. Syn: borehole; drill hole; drilling.

test core

Core removed from a concrete structure by diamond core drilling and tested in a laboratory to determine the strength and other physical properties of the concrete. Also, core removed from a borehole drilled in search of oil and used to determine the porosity of the core and whether oil is present.

test detonator

An instantaneous detonator that has a strength equivalent to that of a detonator with a base charge of 0.40 to 0.45 g PETN.


a. A sampling instrument.

b. A person responsible for carrying out ventilation, dust, or other tests. c. Service company representative who supervises borehole testing operations.

test hole

a. Generally, any borehole drilled to obtain samples whereby the structural and physical characteristics of the rocks penetrated can be determined; more specif., a hole produced by rotary or driving soil-testing tools in the course of obtaining samples used in soil- and foundation-testing work.

b. Usually a small hole drilled ahead and flanking in a working place to ascertain proximity of old workings and to determine water or air content of same. c. A drill hole or shallow excavation for testing an orebody; a test pit. d. A taphole, as in a cementation furnace.

testing bedrock

See: bedrock test.

testing flame

The lowered flame of a miner's flame safety lamp, which is used to detect the presence of small percentages of combustible gases in mine air.

testing machine

A machine used for applying test loads to standard test pieces or to structural members. Machines are available for carrying out tensile, compressive, impact, and fatigue tests.

test lead

Lead free from any silver, and often finely granulated; used in testing or cupelling, assaying, etc.

test paper

Paper (as litmus paper) cut usually in strips and saturated with an indicator or other reagent that changes color in testing for various substances.

test piece

A piece of material prepared in a suitable shape so that it can be tested in a testing machine.

test pit

a. A shallow shaft or excavation made to determine the existence, extent, or grade of a mineral deposit, or to determine the fitness of an area for engineering works, such as buildings or bridges.

b. See: test hole; trial pit.

test ring

An oval iron frame for holding a test or movable cupelling hearth.

test stone

Basanite. Used for testing streak of precious metals.


Said of a point group or of specific crystal forms in the isometric and tetragonal crystal systems that have but one-fourth the crystal faces generated for the equivalent crystal form in the holohedral (most symmetric) crystal class. These complimentary merohedral forms are designated plus or minus and left or right, four forms being required to show all the faces of the holohedral form because each form lacks both a center and mirror planes of symmetry. See also: merohedral.

tetraboron carbide

See: boron carbide.


A crystallographic axis of rotation of 90 degrees , four-fold. CF: axis of symmetry.


a. A trigonal mineral, Bi (sub 2) Te (sub 2) S ; forms foliated masses in auriferous veins, commonly with tellurobismuthite; a source of bismuth. Syn: telluric bismuth; bismuth telluride.

b. The mineral group kawazulite, paraguanajuatite, skippenite, tellurantimony, tellurobismuthite, and tetradymite.


An antiknock constituent of gasoline; Pb (C (sub 2) H (sub 5) ) (sub 4) .


a. Designating or belonging to a system of crystallization having all three axes at right angles and the two lateral axes equal. This system is called tetragonal system.

b. The crystal system in which crystals have one four-fold symmetry axis. c. The crystal system characterized by three orthogonal crystallographic axes, the principal or c axis being a tetrad (4-fold axis), longer or shorter than the two lateral a axes. See also: crystal systems.

tetragonal trisoctahedron

See: trapezohedron.


Having the symmetry or shape of a tetrahedron.


a. An isometric mineral, (Cu,Fe) (sub 12) Sb (sub 4) S (sub 13) , having copper replaced by zinc, lead, mercury, cobalt, nickel, or silver; forms a series with tennantite and freibergite; metallic; crystallizes in tetrahedra; occurs in hydrothermal veins and contact metamorphic deposits; a source of copper and other metals. Syn: gray copper ore; gray copper; panabase; panabasite; stylotypite.

b. The mineral group freibergite, giraudite, goldfieldite, hakite, tennantite, and tetrahedrite.


An isometric crystal form of four faces, each an equilateral triangle; the alternate faces of an octahedron. Adj: tetrahedral.


An isometric crystal form (hk0) of 24 faces, each an isosceles triangle, so arranged that four faces appear to replace each face of a cube (hexahedron).


An atom, or group, having four valence bonds.


a. Having a valence of 4.

b. Having four valences; e.g., chlorine, which has valences of 1, 3, 5, and 7.


a. A hole; bore; a chimney, as for smoke.

b. The tuyere of a furnace.


The general physical appearance or character of a rock, including the geometric aspects of, and the mutual relations among, its component particles or crystals; e.g., the size, shape, and arrangement of the constituent elements of a sedimentary rock, or the crystallinity, granularity, and fabric of the constituent elements of an igneous rock. The term is applied to the smaller (megascopic or microscopic) features as seen on a smooth surface of a homogeneous rock or mineral aggregate. The term structure is generally used for the larger features of a rock. The two terms should not be used synonymously, although certain textural features may parallel major structural features. Confusion may arise because in some languages, e.g., French, the usage of texture and structure are the reverse of the English usage. CF: structure.


A monoclinic mineral, Y (sub 3) Si (sub 3) O (sub 10) (OH)(?) ; red to pink; in pegmatites.


A metallic element resembling lead in physical properties; the metal is silvery-white, but turns bluish-gray in air. Symbol, Tl. Occurs in crooksite, lorandite, and hutchinsonite. It is also present in pyrites and is recovered from the roasting of this ore in the manufacture of sulfuric acid and from the smelting of lead and zinc ores. Used in low-melting glasses, photocells, and infrared detectors.


a. The line of continuous maximum descent from any point on a land surface; e.g., the line of greatest slope along a valley floor, or the line crossing all contour lines at right angles, or the line connecting the lowest points along the bed of a stream. Etymol: German Talweg, valley way. Also spelled: talweg.

b. In physical geography, a term adopted into English usage signifying the line of greatest slope along the bottom of a valley; i.e., a line drawn through the lowest points of a valley in its downward slope. It thus marks the natural direction of a watercourse. c. In hydraulics, the line joining the deepest points of a stream channel. d. By many geomorphologists, the term is used as a syn. for valley profile. e. The center line of the principal navigational channel of a waterway constituting a boundary between political subdivisions.


a. A mixture of kainite and halite.

b. Carbon oxysulfide, COS, as a natural gas.


A hexagonal mineral, Ca (sub 6) Si (sub 2) (CO (sub 3) ) (sub 2) (SO (sub 4) ) (sub 2) (OH) (sub 12) .24H (sub 2) O ; white; fibrous.

thaw house

A small building, designed for thawing dynamite, of such size as to provide enough thawed dynamite for a day's work.


a. A method of working permanently frozen ground in which water at a temperature of from 50 to 60 degrees F (10 to 15.6 degrees C) is pumped through pipes down into the frozen gravel. The pipes through which the water is pumped are called sweaters. See also: steam thawing; thaw pipe.

b. In dynamiting, warming to reduce risk of premature explosion that might originate from rupture of frozen crystal. Performed in thaw house or thawing kettle using steam or hot water. With modern methods of explosive manufacture, the need has practically disappeared.

thawing kettle

A double kettle, built somewhat like a farina boiler, having two compartments, an outer compartment, which is filled with hot water and which entirely surrounds the inner compartment that contains the dynamite to be thawed. It is provided with a lid for retaining the heat.

thaw pipe

A string of pipe lowered into a string of drill rods that is frozen in a borehole drilled into permafrost, through which water is circulated to thaw the ice and free the drill rods. See also: thawing.

thaw shed operator

In the coke products industry, one who thaws frozen materials in railroad cars by heating sections of shed where cars are spotted.


See: translucent humic degradation matter.


A carbonaceous constituent of torbanite, occurring in the form of a solidified clear, jellylike substance, something like solidified dopplerite, but probably of unlike chemical composition.

thematic mapper

A cross-track scanner deployed on Landsat that records seven bands of data from the visible through the thermal IR regions. See: multispectral scanner.


An orthorhombic mineral, Na (sub 2) SO (sub 4) ; soft; forms masses and crusts in evaporite deposits and around fumaroles; a source of sodium sulfate. Also called verde salt.


A precision surveying instrument that is used for measuring angular distances in both vertical and horizontal planes.

theoretical depression

The water gage produced by an imaginary fan that is perfect and is connected to an evase chimney of infinite height to eliminate kinetic losses at discharge. Its calculated value depends only on the speed of the blade tips and on the shape of the blades. See also: manometric efficiency; initial depression.

theoretical fan depression

The depression that can be produced by a perfect fan.

theoretical tonnage

See: probable reserves.

theoretical yield

The maximum yield (as shown by the washability curve) of a product with a specified percentage of ash.

theory of lateral secretion

The theory that the contents of a vein or lode are derived from the adjacent country rock by a leaching process, in which either superficial water or thermal water is involved.

theory of machines

Comprises the study of the relative motion between the parts of a machine and the study of the forces that act on those parts. See also: machine design.


A group of mafic plutonic rocks composed of calcic plagioclase, feldspathoids, and augite, with lesser amounts of sodic sanidine and sodic amphiboles and accessory olivine; also, any rock in that group; the intrusive equivalent of tephrite. Theralite grades into nepheline monzonite with an increase in the alkali feldspar content, into gabbro as the feldspathoid content diminishes, and into diorite with both fewer feldspathoids and increasingly sodic plagioclase. The term, defined by Rosenbusch in 1887, is derived from the Greek word for eagerly looked for, not from the island of Thera (Santorini).


Equals 100,000 Btu (105,500 kJ).


Hot or warm; applied to springs that discharge water heated by natural agencies.

thermal-acceptance ratio

A physiological method of assessing the effect of a given climate upon workers, that is based on the ratio between the heat actually lost by the body via the skin, lungs, etc., and the maximum that can be lost in the prevailing conditions.

thermal analysis

a. A method for determining transformations in a metal by noting the temperatures at which thermal arrests occur. These arrests are manifested by changes in slope of the plotted or mechanically traced heating and cooling curves.

b. The study of chemical and/or physical changes in materials as a function of temperature, i.e., the heat evolved or absorbed during such changes.

thermal boring

Use of high-temperature flame to fuse rock in drilling. Heat comes from ignition of kerosene with oxygen or other fuel system, at bottom of drill hole, and water with compressed air may be used to flush out the products.

thermal capacity

a. Heat required to raise the temperature of a body 1 degrees C. Syn: heat capacity.

b. The amount of heat that a clay product will absorb, usually expressed in British thermal units per degree Fahrenheit (kilojoules per degree Celsius).

thermal conductivity

a. The time rate of transfer of heat by conduction, through unit thickness, across unit area for unit difference of temperature.

b. A measure of the ability of a material to conduct heat. Typical values of thermal conductivity for rocks range from 3 to 15 mcal/cm/s/ degrees C (12.6 to 62.8 kJ/cm/s/ degrees C). Syn: heat conductivity; thermal diffusivity of strata.

thermal cutout

A device fitted in hydraulic power systems underground so that temperatures cannot rise above about 85 degrees C. It is a safeguard against fire risk due to a rapid rise in temperature if the fluid circuit is interrupted by wrong manipulation of valves, etc.

thermal diffusivity of strata

See: thermal conductivity.

thermal drying

a. The evaporation of water by thermal means from a mixture of coal and water. See also: McNally-Vissac dryer; multilouvre dryer; Raymond flash dryer; cascade coal dryer; flash coal dryer; fluidized bed dryer.

b. The application of heat (generally hot-air currents) to wet coals and other materials and the evaporation of the free moisture and also part of the inherent moisture.

thermal efficiency

The ratio of the electric power produced by a powerplant to the heat value of the fuel consumed; thus, a measure of the efficiency with which the plant converts thermal energy to electric energy. Symbol, eta .

thermal electromotive force

The electromotive force generated in a circuit containing two dissimilar metals when one junction is at a different temperature from the other.

thermal emissivity

The thermal emissivity, or heat transfer coefficient, of a rock surface is the rate at which heat will flow from rock to air, per unit area for 1 degree temperature difference. This varies with color and other surface characteristics. Measured in W/m (super 2) .K.

thermal expansion

The increase in linear dimensions and volume that occurs when materials are heated and that is counterbalanced by a contraction of equal amount when the materials are cooled.

thermal gradient

In the Earth, the rate at which temperature increases with depth below the surface. In a mine, this is usually estimated at 5.3 degrees F/1,000 ft (1 degrees C/100 m) of shaft depth. Some variability with time of day is typically observed.

thermal metamorphism

A type of metamorphism resulting in chemical reconstitution controlled by a temperature increase, and influenced to a lesser extent by confining pressure; there is no requirement of simultaneous deformation. See also: pyrometamorphism. CF: contact metamorphism; load metamorphism; static metamorphism. Syn: thermometamorphism.

thermal precipitator

An instrument for obtaining information regarding the number of particles present in unit volume of a dust cloud, together with their size distribution. This is probably the most efficient instrument used for dust counts since its efficiency is practically 100% for all particles from 0.2 to 10 mu m in diameter. See also: Hexhlet sampler; dust sampling.

thermal probe

A device used for measuring the heat flow out of ocean bottom sediment.

thermal prospecting

A system of geophysical prospecting based on measuring underground temperatures or temperature gradients and relating their irregularities to geological deformation.

thermal reactor

A nuclear reactor in which the fission chain reaction is sustained primarily by thermal neutrons. Most reactors are thermal reactors.

thermal-release water spray

A device that brings water sprays into action when heating occurs on roadway belt conveyors. The local heat fuses an element holding taut wires. On release by fusion, the wires allow spray valves to open and the water cools the affected area.

thermal resistance

See: resistance.

thermal resistivity

See: resistivity.

thermal separation

The separation of minerals and metals by heat. The method is used, e.g., to remove impurities from rock salt. The crude salt is first exposed to radiant heat. The impurities absorb the heat and become warm, while the rock salt transmits the radiant heat and remains cool. The warm, impure particles adhere slightly to a belt covered with heat-sensitive resin, while the salt remains free. Separation takes place at the end of the belt. The cool salt is thrown into one container, while the adhering impurities drop directly into another.

thermal shock

Failure of a material, esp. a brittle material, due to the thermal stress of rapidly rising or falling temperature.

thermal shock resistance

The ability to withstand sudden heating, cooling, or both without cracking or spalling.

thermal spalling

The chipping or spalling of ceramic ware by repeated heating and cooling.

thermal spring

A spring whose water temperature is appreciably higher than the local mean annual atmospheric temperature.

thermal value (volatile matter)

The calorific value of volatile matter in therms per ton of dry coke, of the gas given off when dry coke, ground to pass a 36-mesh B.S. test sieve, is heated under standard conditions.

thermal water

Water, generally of a spring or geyser, whose temperature is appreciably above the local mean annual air temperature.

thermic boring

a. A method of boring holes in concrete under the high temperature generated by a burning steel tube, known as a lance. This is packed with steel wool, through which a jet of suitable gas flows to ignite the end of the lance and keep it burning.

b. See: jet piercing.

thermic drilling

See: jet piercing.


An electrical resistor made of a material whose resistance varies sharply in a known manner with the temperature. Thermistors are commonly used for shipboard oceanographic temperature measurements because of their percentage response to unit temperature change and their great sensitivity.


a. Any fossil combustible substance.

b. An intimate mixture of aluminum powder and powdered iron oxide that when caused to react by strong heating emits a great deal of heat and yields alumina and a white-hot molten mass of metallic iron.

thermit process

The energetic action of finely divided aluminum on a metallic oxide, when heated together, is utilized for the production of metallic iron manganese, chromium, tungsten, molybdenum, uranium, etc. The aluminum combines directly with the oxygen of the oxide, and the heat emitted by the reaction is sufficient to promote the fusion of the reduced metal.


See: thermometer anemometer.


Frequently used in geophysics to describe the decrease in temperature that always occurs at great depths.


Two conductors of different metals joined together at both ends, producing a loop in which an electric current will flow when there is a difference in temperature between the two junctions. Abbrev., tc.


The mathematical treatment of the relation of heat to mechanical and other forms of energy.

thermoelectric conversion

The conversion of heat into electricity by the use of thermocouples.


Electricity involved in thermoelectric phenomena. Specif., electricity accumulated or put in motion by thermoelectric action.

thermoelectric metals

Metals or alloys used in thermocouples for measuring high temperatures. Platinum, nickel, copper, rhodium, etc., are much used.


A self-recording thermometer that gives a continuous trace of air temperature on a rotating drum worked by clockwork. It is mainly used for recording variations in temperature rather than actual temperatures.


The property of minerals to emit light when heated. It results from the release of energy stored by displaced electrons trapped in a crystal structure. See also: calorescence. CF: luminescence.


See: thermal metamorphism.


An instrument for determining temperature usually by means of a scale graduated directly in temperature units and consisting typically of (1) a device having a bimetallic element, the expansion or contraction of which indicates a change in temperature, or (2) a glass bulb attached to a fine tube of glass with a numbered scale etched on it or fastened to it and containing a liquid (as mercury or cooled alcohol) that is sealed in and rises and falls with changes of temperature and that indicates the temperature by the number at the top of the column of liquid.

thermometer anemometer

An anemometer consisting of two thermometers, one with an electric heating element (battery powered) connected to the bulb. The heated bulb cools in an airstream, and the difference in temperature as registered by the heated and unheated thermometers can be translated into air velocity by a conversion chart. It is nondirectional and can be made safe (6 V) for use in explosive atmospheres. Syn: thermoanemometer.

thermometer float

This instrument is used for studying the temperature structure in the upper 10 m of water. The instrument is in two sections; a float, which contains a spooling winch from which the sensing unit is lowered, and an indicator case, which contains the remote indicating equipment and remote control system. The two sections are connected by an electric cable and flexible shaft, supported by net floats. The indicator case is clear lucite. It contains the indicating meter and electric circuitry for temperature determination. It also contains a Veeder-Root counter, which indicates directly in centimeters the depth at which the sensing unit is located. This instrument makes it possible to read temperature to within 0.1 degrees C and to know the depth of the sensing unit to within + or -0.5 cm. It is intended to be used at sea from a skiff or tender rather than from the research vessel itself.

thermometer scales

Two thermometer scales are in general use, the Fahrenheit, which is generally used in engineering, and the Celsius, which is almost universally used in scientific work. The Fahrenheit scale has the freezing point at 32 degrees F and the boiling point at 212 degrees F, whereas the Celsius scale has the freezing point at 0 degrees C and the boiling point at 100 degrees C. The Celsius scale is commonly called the centigrade scale.

thermometric fan test

A method of assessing the efficiency of a mine fan by comparing the temperature rise in an ideal isentropic fan for a given fan pressure with the measured temperature rise actually occurring in the fan under consideration when producing the same fan pressure. The ratio of isentropic temperature rise to the actual temperature rise across the fan gives the fan efficiency. The method gives an accuracy of + or -5%. See also: overall ventilation efficiency.


An orthorhombic mineral, Na (sub 2) CO (sub 3) .H (sub 2) O ; forms flat, white, water-soluble crystals in some lakes and alkali soils, also a saline residue.


Natural migration of moisture from a relatively warm part of a mass of soil toward a cooler part. See also: electro-osmosis.


An apparatus consisting of a number of thermoelectric couples (as of antimony and bismuth or of copper sulfide and German silver) combined so as to multiply the effect used; (1) to generate electric currents for various purposes, and (2) in a very sensitive form for determining intensities of radiation due esp. to its heating effect.


In plastics, rigid material that temporarily becomes soft when heated and can then be molded into a shape that it will retain on cooling. Ant. for thermosetting, a material that reacts chemically on heating (curing) and is then resistant to deformation when reheated.

thermoscopic bar

Small ceramic bar of specified composition that softens at certain temperatures. See also: Holdcroft thermoscope bar.


An automatic device for regulating temperature (as by opening or closing the damper of a heating furnace or by regulating the supply of gas) and commonly utilizing either the differential expansion of solids or the vapor pressure of liquids.

Thetis hairstone

Coarsely crystalline quartz containing inclusions of asbestiform amphibole, esp. hornblende or actinolite, that may be tangled or wound into a ball. See also: Venus hairstone; sagenitic quartz.


A relative term applied to sedimentary beds variously defined as more than 2.5 in (6.4 cm) to more than 40 in (100 cm) in thickness; specif. said of a bed whose thickness is in the range of 2 to 4 ft (60 to 120 cm), a bed greater than 120 cm being very thick-bedded. CF: tight-bedded; thin-bedded.


A vessel or apparatus for reducing the proportion of water in a pulp by means of sedimentation.


a. The process of concentrating a relatively dilute slime pulp into a thick pulp, i.e., one containing a smaller percentage of moisture, by rejecting liquid that is substantially solid free. Settling is another name for the same operation.

b. The concentration of the solids in a suspension with a view to recovering one fraction with a higher concentration of solids than in the original suspension.


a. The distance at right angles between the hanging wall and the footwall of a lode or lens.

b. As used in mine subsidence, the thickness of a bed or seam of mineral is the distance from its roof to its floor, measured at right angles to the plane of stratification. c. That dimension designed to lie at right angles to the face of the wall, floor, or other assembly.

thickness contour

See: isopach.

thickness line

See: isopach.

thick seam

In general, a coal seam over 4 ft (1.22 m) in thickness. See also: medium-thickness seam.

thick-wall sampler

A soil sampler made from a steel tube having a wall thickness greater than 16 gage. See also: drive sampler. CF: Shelby tube; Shelby-tube sampler.

Thiess process

A chlorination process for recovering gold from its ore. For each ton (0.9 t) of ore in a revolving drum, 130 gal (492 L) of water, 30 lb (13.6 kg) of lime chloride, and 36 lb (16.3 kg) of concentrated sulfuric acid are added, and the drum is revolved for some time. A solution of gold chloride is thus obtained.


a. The floor of a coal seam. See also: underclay.

b. Eng. Seat earth or pavement of underclay directly underlying a coalbed, Newcastle. c. A thin stratum of fireclay.


An oval iron ring around which a rope end is bent and fastened to form an eye.

thimble joint

A sleeve joint packed to allow longitudinal expansion. A slip expansion joint.


A relative term applied to sedimentary beds variously defined as less than 1 ft (30 cm) to less than 0.4 in (1 cm) in thickness; specif. said of a bed whose thickness is in the range of 2 to 24 in (5 to 60 cm), a bed less than 5 cm but more than 1 cm thick being very thin-bedded. CF: tight-bedded; thick-bedded.


A tufa deposit of fibrous calcite pseudomorphous after an unknown precursor occurring on an enormous scale in northwestern Nevada; also occurs about Mono Lake, CA. It forms layers of interlaced pale yellow or light brown crystals, commonly skeletal with pyramidal terminations. Syn: thinolitic tufa.

thinolitic tufa

See: thinolite.

thin out

To grow progressively thinner in one direction until extinction. The term is applied to a stratum, vein, or other body of rock that decreases gradually in thickness so that its upper and lower surfaces eventually meet and the layer of rock disappears. The thinning may be original or due to truncation beneath an unconformity. Syn: pinch out; wedge out.

thin seam

In general, a coal seam 2 ft (0.6 m) and under in thickness. See also: economic coal reserves.

thin-seam miner

An adaptation of the auger surface miner, the thin-seam miner cuts an entry 8 ft (2.4 m) wide and up to 5 ft (1.5 m) high into coal located under the highwall in surface mines.

thin section

a. A fragment of rock or mineral mechanically ground to a thickness of approx. 0.03 mm, and mounted between glasses as a microscope slide. Rocks and most minerals except the oxides and sulfides of the metals are translucent to transparent in thin section, and the optical properties of each mineral can be studied with the microscope. See also: polished section.

b. A rock or mineral slice cut for study by transmitted light with a polarized-light microscope. It may also be polished for study with a reflected-light microscope. c. A coal seam less than its normal thickness.

thin stock

Slabs of stone employed for wainscoting, flooring, etc.

thin-wall bit

A coring bit the kerf or wall thickness of which is about one-half or less that of the wall thickness of the same outside-diameter-size standard coring bit.

thin-wall drive sampler

See: Shelby tube; thin-wall sampler.

thin-wall sampler

A soil-sampling barrel made from steel tubing having approx. a 16-gage wall thickness. Syn: thin-wall drive sampler; thin-wall tube sampler. CF: Shelby tube.

thin-wall tube sampler

See: thin-wall sampler.

Thiobacillus ferrooxidans

A bacterial strain that catalyzes the oxidation of ferrous iron (Fe (super +2) ) to ferric iron (Fe (super +3) ).

Thiobacillus thiooxidans

A bacterial strain that catalyzes the oxidation of sulfur to sulfate (SO (sub 4) (super -2) ).


A derivative from thio-urea. In the flotation process, it is used as a collector agent of low solubility in water; it is sometimes used in copper or galena flotation.


Powerful collector agents in the flotation process where xanthates fail.


See: thiophene.


Kerite containing 9% sulfur.


A liquid; C (sub 4) H (sub 4) S ; analogous to furan and pyrrole in its heterocyclic structure and resembles benzene both physically and chemically except for its greater reactivity. Found in small amounts (as up to 0.5% by weight) in benzene from coal tar unless it has been removed by treatment with sulfuric acid. Used chiefly in organic synthesis. Syn: thiofuran.

thiophile elements

Equivalent to chalcophile. Literally, sulfur-loving. See also: chalcophile.


Sulfydric flotation agents, produced by reacting phosphorus pentasulfide with phenols, alcohols, etc., and marketed as Aerofloats.

third-class lever

A lever to which force is applied between the fulcrum and the work point.

Third Theory of Comminution

The Third Theory states that the specific work input required for size reduction is inversely proportional to the square root of the product size, less the work required to form the feed.


a. A cross hole or ventilation passage between two headings. See also: thurl; thurling; thirling.

b. To cut out the lost coal between two workings or headings. c. To cut through from one working into another.


a. The driving of a proposed roadway from two points some distance apart to meet each other; the connecting of underground roadways or shafts.

b. See: thirl; crosscut; through cut. c. See: holing; stenton.

this vein

A notice claiming a location upon this vein has only one meaning. It raises an inference that the notice was posted upon or in close proximity to a vein or lode, although, as a fact, no vein or lode then was exposed.

thixotropic fluid

Clays termed thixotropic are those that reveal this property by weakening when they are remolded and by increasing in strength when allowed to stand undisturbed. See also: remolding. An important characteristic of oil-well drilling fluids.


a. The property of certain colloidal substances, such as a thixotropic clay, to weaken or change from a gel to a sol when shaken, but to increase in strength upon standing.

b. The property of a material that enables it to stiffen in a relatively short time on standing, but upon agitation or manipulation to change to a very soft consistency or to a fluid of high velocity, the process being completely reversible. Used in muds for drilling deep oil wells since, if the drill stops, rock chips on the way to the surface are held in suspension instead of settling to the bottom where they might jam the drilling bit. See also: gel; plastic deformation.


A silica-oversaturated (quartz-normative) basalt, characterized by the presence of low-calcium pyroxenes (orthopyroxene and/or pigeonite) in addition to clinopyroxene and calcic plagioclase. Olivine may be present in the mode, but neither olivine nor nepheline appear in the norm. CF: basalt.


A variety of siderite that is found massive and in pyramidal crystals.

Thomas converter

A bottom-blown basic pneumatic converter having a basic bottom and lining, usually dolomite, and employing a basic slag.

Thomas-Gilchrist process

Conversion of iron to steel in basic-lined Bessemer converter. Phosphorus combines with dolomite in this lining to produce basic slag.

Thomas slag

The finely powdered basic slag obtained in the Thomas-Gilchrist process. It consists of phosphates and is used as a fertilizer.

Thomas steel

Steel made in a Bessemer converter using a basic refractory lining. The process was developed by Thomas and Gilchrist. In Europe such steel is known as Thomas steel; in Great Britain, Thomas-Gilchrist steel; and in the United States, basic Bessemer steel.

Thompson arc cutter

See: arc cutter.


An orthorhombic mineral, Na (sub 4) Ca (sub 8) [Al (sub 20) Si (sub 20) O (sub 80) ].24H (sub 2) O ; zeolite group; pseudotetragonal; occurs in amydules and crevices in basalts and tuffs; also an alteration of anorthite. Also called ozarkite.

Thompson pilot shoulder reamer

A reaming or coring bit with an articulated steel pilot protruding about 36 in (91 cm) beyond the face of the bit. The diameter of the pilot is slightly smaller than the set inside diameter of the bit; its upper end is a piston fitted tightly inside a single-tube barrel with its attached coring bit. When lowered into a borehole in which a deflection wedge has been set, the pilot section forces the coring bit to ream out the first part of the deflected hole at a point about 20 in (51 cm) above the tip of the wedge. Reaming is continued to about 6 in (15 cm) below the wedge tip, at which point the pilot shoulder reamer is withdrawn and replaced by a bullnose or deflection bit.

Thompson wedge

A retrievable type of deflecting wedge. See also: deflecting wedge.


A monoclinic mineral, NaCaAlF (sub 6) .H (sub 2) O ; dimorphous with pachnolite; forms small, white prismatic crystals on cryolite.


A monoclinic mineral, SnTa (sub 2) O (sub 6) ; forms a series with foordite; brown; in pegmatite at Katanga, Congo.


A rare refractory oxide, ThO (sub 2) .

thorian gummite

See: thorogummite.


An isometric mineral, ThO (sub 2) ; commonly contains lanthanides; has fluorite structure; forms a series with uraninite; highly radioactive and metamict; sp gr, 9.7; in pegmatites; in placers associated with zircon, ilmenite, geikielite, thorite, and other heavy minerals; an important source of uranium and thorium. Also called isometric thorium.

thorian uraninite

A variety of uraninite containing thorium in partial substitution for uranium.

thorium borides

Two borides are known: ThB (sub 4) (gray) and ThB (sub 6) (deep red). More attention has been paid to the tetraboride, the properties of which are melting point, >2,200 degrees C (but oxidizes slowly above 1,000 degrees C); thermal expansion, 5.9X10 (super -6) (20 to 1,000 degrees C); sp gr, 8.45 g/mL; modulus of rupture (20 degrees C), 20,000 psi (138 MPa) . Some properties of ThB (sub 6) are melting point, 2,200 degrees C; sp gr, 7.1.

thorium carbides

Two carbides are known: ThC, melting point, 2,625 degrees C; ThC (sub 2) , melting point, 2,655 degrees C. These special carbides are of potential interest in nuclear engineering.

thorium disintegration series

The series of radioactive elements produced as successive intermediate products when the element thorium (thorium 232) undergoes its spontaneous natural radioactive disintegration into stable lead (lead 208).

thorium mineral

One of several minerals including monazite, in which Th replaces rare earths; thorite, ThSiO (sub 4) ; and thorianite, ThO (sub 2) .

thorium nitride

Three thorium nitrides have been reported: ThN, Th (sub 2) N (sub 3) , and Th (sub 3) N (sub 4) .

thorium sulfides

Three thorium sulfides have been reported: Th (sub 4) S (sub 7) , Th (sub 2) S (sub 3) , and ThS . Crucibles made of these sulfides have been used as containers for molten cerium.


A tetragonal mineral, Th(SiO (sub 4) ) (sub 1-x) (OH) (sub 4x) ; may contain up to 31% uranium; has zircon structure. Differs from thorite (1) in being secondary, formed by the alteration of primary thorium minerals including thorite itself; (2) in not being metamict but forming crystalline aggregates; and (3) in containing essential (OH). Syn: thorian gummite; mackintoshite; maitlandite.


A name for radon 220, a member of the thorium disintegration series; symbol, Tn; emits alpha particles; and half-life, 5.5 s. Also called emanation; thorium emanation.


A mineral, Na (sub 2) (Th,RE)(Mn,Ta,Fe)H (sub 2) [(Si,P)O (sub 4) ] (sub 3) ; metamict; dark brown to black.


See: yttrotungstite.

thorough joints

Vertical joints affecting all the strata, as opposed to cricks or looses, oolite quarries, Northamptonshire, United Kingdom. Syn: upright joints.


A monoclinic mineral, (Sc,Y) (sub 2) Si (sub 2) O (sub 7) ; may contain up to 42% yttrium replacing scandium; weakly radioactive; grayish green where fresh, altering to white to reddish gray; in pegmatites associated with monazite, euxenite, beryl, struvite, and possibly fergusonite; the only known mineral rich in scandium.

Thoulet's law

Heavy mineral suites increase in complexity with decreasing geologic age.

Thoulet solution

A yellowish-green, transparent, aqueous solution of potassium mercuric iodide, having a maximum specific gravity of 3.19. Also known as Sonstadt solution. Used in the sink-float process of mineral separation.


a. An extremely small vein, even thinner than a stringer.

b. A more or less straight line of stall faces, having no cuttings, loose ends, fast ends, or steps. c. To reeve rope or cable through a sheave or block and tackle.

thread cutter

A name sometimes applied to a diamond crystal having the shape of an octahedron.

thread-lace scoria

A scoria in which the vesicle walls have burst and are represented only by an extremely delicate three-dimensional network of glass threads. See also: reticulite.

three-cone bit

See: goniometer. �d �� &� z D�� � J DICTIONARY TERMS:three-cone bit See: roller rock bit. Also called tr See: roller rock bit. Also called tricone bit.

three-dimension dip

In seismic prospecting, the true dip of a reflection or refraction horizon found by exploration and calculation. See: true dip.


An axial symmetry operation requiring three repetitions to complete 360 degrees or return to identity. Syn: triad.

three-high mill

Consists of three horizontal rolls, one above the other, each rotating continuously in one direction only, the piece being rolled between the bottom and middle, and middle and top rolls alternately.

three-hinged arch

An arch hinged at its abutments and at its crown with the advantage that each half can sink in relation to the other without damaging the arch.

three-jaw chuck

A drill chuck having three serrated-face movable jaws that can be made to grip and hold fast an inserted drill rod. See also: chuck.


In crystallography, a crystal of three parts united by the same twinning law. Syn: trilling.

three-part line

A single strand of rope or cable doubled back around two sheaves so that three parts of it pull a load together.

three-phase circuit

Usually a three-wire circuit using alternating current with three equal voltages. This should not be confused with the three-wire service supplying 110 V and 220 V. This latter is merely a two-voltage single-phase circuit arrangement and is used almost universally to provide power and lighting to homes and small business establishments.

three-phase current

Alternating current in which three separate pulses are present, identical in frequency and voltage, but separated by 120 degrees .

three-phase inclusion

An inclusion consisting of a liquid with a gas bubble and a crystal within a crystal. See also: negative crystal; inclusion.

three-piece set

A set of timber used in ground that requires greater support than a two-piece set or stull will provide. A cap is supported by two posts often spread apart at the bottom to give greater stability. See also: timber set; four-piece set.

three-point problem

a. In surveying, a method used to orient underground workings via three plumblines suspended in a vertical shaft.

b. The problem in plane table surveying of locating precisely the point at which the table is set up, using three fixed points that are visible from the plane table. c. The problem of determining dip and strike of a plane from elevations determined at three known points not in a straight line.

three-product washing

A method in which the cleanest fraction of the coal with an ash content of 1% to 2% (for hydrogenation, etc.) is separated; the remainder giving coal with an ash content of 10% to 15% (for boiler firing, etc.) and finally incombustible shale.

three-shift cyclic mining

A system of cyclic mining on a longwall conveyor face, with coal cutting on one shift, hand filling and conveying on the next, and ripping, packing, and advancement of the face conveyor on the third shift. The system restricts coal production to one shift.

three-term process controller

Instrument that automatically regulates a process in proportional, integral, and derivative terms, thus neutralizing and removing the errors that arise during operation.

three-throw ram pump

This type of pump consists essentially of three single-acting ram pumps side by side, either vertical or horizontal, and driven from a triple crankshaft with cranks set at angles of 120 degrees . The three-throw pump can deal with heads up to 1,000 yd (900 m) in a single lift.

three-wire system

A voltage improvement system that consists of the series operation of two generators. One circuit of a mine is fed from one generator, and a second circuit is fed from the other generator. The mine track or return is common to both generators and is connected between the generators. This method provides high voltage for transmission of power, yet the individual circuits provide normal low-voltage power. In effect, this is the Edison three-wire system, wherein the rails form the neutral third wire. The third wire (mine track) carries only the unbalance between the loads on the two separate circuits.


a. In geochemical prospecting, the limiting anomalous value below which variations represent only normal background effects and above which they have significance in terms of possible mineral deposits.

b. In analytical chemistry, the limiting sensitivity of an analytical method, the detection limit.

Threshold Limit Value

A time-weighted average concentration under which most people can work consistently for 8 hours a day, day after day, with no harmful effects. A table of these values and accompanying precautions is published annually by the American Conference of Governmental Hygienists.


a. The part of a blast furnace at the top of the stack.

b. The zone of decreased cross section found between the port area and the furnace chamber in some designs of open-hearth steel furnaces. c. The submerged passage connecting the melting end to the working end of a glass tank furnace; the refractory blocks forming the sides of the throat are known as throat cheeks, sleeper blocks, or dice blocks; the refractories for the top are the throat cover. See also: submarine throat. d. The least thickness of a weld, the calculation of its strength being based on the thickness at the throat.

throat of crusher

Point at which the rock is discharged. Its short dimension varies, depending upon whether the swing jaw is in the open or closed position.


To obstruct the flow of, as steam to an engine esp. by a throttle valve.

throttle valve

A valve designed to regulate the supply of a fluid (as steam or gas and air) to an engine.


A passage cut through a pillar to connect two rooms.

through cut

An excavation between parallel banks that begins and ends at original grade. See also: thirling.


See: stenton.


Quantity of material passed through the mill or a section thereof in a given time or at a given rate.

through ventilation

The normal ventilation produced in a mine as the air flows from the intake to the return, as opposed to ventilation produced locally by auxiliary fans.


a. The amplitude of shake of a vibratory screen, concentrating table, jigger conveyor, etc.

b. Lateral displacement of a screen, shaking table, or crushing surface in motion. c. The projection of broken rock during blasting. See also: flyrock. d. The distance from an air supply opening measured in the direction of air flow, from the opening to the point where the air velocity is 50 ft/min (15.2 m/min). e. The amount of vertical displacement up (upthrow) or down (downthrow) produced by a fault; sometimes, loosely, a dislocation not vertical, the direction being specified. See also: heave; perpendicular throw; stratigraphic throw. f. The vertical component of the net slip on a fault.

thrower belt

See: boxcar loader.

throwing clay

Clay plastic enough to be shaped on a potter's wheel.


a. Faulted or broken up by a fault.

b. Turned, as a piece of ceramic ware on a potter's wheel.

throw of crusher

See: stroke of crusher.

throwoff switch

Aust. A switch by means of which an obstruction is thrown across the rails of a track, causing the derailment of the trucks. A derailing switch.

throwout bearing

a. A bearing, sliding on a clutch jackshaft, that carries the engage and disengage mechanism.

b. A bearing that permits a clutch throwout collar to slide along the clutch shaft without rotating with it.


a. An overriding movement of one crustal unit over another, such as in thrust faulting.

b. See: thrust fault; fault. c. A crushing of coal pillars caused by excess weight of the superincumbent rocks, the floor being harder than the roof. CF: creep. d. The ruins of a fallen roof, after pillars and stalls have been removed. e. The weight or pressure applied to a bit to make it cut.

thrust arm

A cable-controlled bar that can slide by power in two directions.

thrust bearing

a. A bearing that resists attempts of a shaft to move along its axis.

b. A bearing designed to carry axial loads on a shaft.

thrust block

The antifriction part of the thrust yoke attached to the drive rod in the swivel head of a diamond-drill machine. Also called cage; friction head; thrust collar. See also: thrust sheet.

thrust borer

Mechanism for forcing a hole through an embankment for the insertion of pipes or cables.

thrust fault

a. A fault with a dip of 45 degrees or less over much of its extent, on which the hanging wall appears to have moved upward relative to the footwall. Horizontal compression rather than vertical displacement is its characteristic feature. CF: normal fault. Partial syn: reverse fault. Syn: thrust; overthrust.

b. A reverse fault that is characterized by a low angle of inclination with reference to a horizontal plane. c. A reverse fault heading at a high angle.

thrust nappe

See: thrust sheet.

thrust plane

a. The surface of a thrust fault, when the surface is planar.

b. The plane of a thrust or reversed fault. Syn: overthrust plane.

thrust plate

The upper and/or lower race parts of the thrust bearing in the thrust block or cage on the drive rod in a diamond-drill swivel head. Syn: thrust race. See also: thrust sheet.

thrust race

See: thrust plate.

thrust sheet

The body of rock above a large-scale thrust fault whose surface is horizontal or very gently dipping. Syn: thrust block; thrust nappe; thrust plate.

thrust washer

A washer that holds a rotating part from sideward movement in its bearings.

thrust yoke

The part connecting the piston rods of the feed mechanism on a hydraulic-feed diamond-drill swivel head to the thrust block, which forms the connecting link between the yoke and the drive rod, by means of which link the longitudinal movements of the feed mechanism are transmitted to the swivel-head drive rod. Also called back end; cage.


An intense pink variety of zoisite containing manganese; an ornamental stone.

Thum-Balbach process

A silver refining process using carbon cathodes, dore anodes, and a silver nitrate-nitric acid electrolyte. The silver is scraped off the bottom as crystals.

thumb-marked fracture

The minute ripples or thumbmarks characteristic of the fractured surface of amethyst.

Thum furnace

A gas-fired furnace esp. for the treatment of zinc ore that is high in lead.


a. A stone or stony concretion, esp. if elongated and tapering, found in the ground and ignorantly supposed to have fallen from the sky.

b. A nodule or mass of iron pyrites found in English chalk formations.

thunder egg

A popular term for a small, geodelike body of chalcedony, opal, or agate that has weathered out of the welded tuffs or lava, particularly from central Oregon.


A monoclinic mineral, [Fe(OH) (sub 2) (AlSi (sub 3) O (sub 10) )].3[(Mg,Fe)(OH) (sub 2) ] ; pseudohexagonal; forms monoclinic plates having micaceous cleavage; an iron-rich chamosite.


S. Staff. To cut through from one working into another. Also spelled thirl.


A passage cut from room to room, in post-and-stall working. See also: thirl; thirling.


A short tunnel driven between two or more veins where they are nearly vertical.


A gas-filled valve or tube in which the initiation of current in an ionized gas or vapor is controlled by the voltage applied to a control electrode.

Thyssen gravimeter

An early gravity meter of the unstable equilibrium type.