Appendix:Dictionary of Mining, Mineral, and Related Terms/U/1

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A popular type of rotary bit used in British mining practice. It has two cutting legs, although some American and German bits employ three legs. A core is formed between the legs, which is broken off as cutting proceeds; some bits have a core-cutting device consisting of a tungsten carbide tip in the center.

Udden grade scale

A logarithmic grade scale devised by Johan A. Udden (1859-1932), U.S. geologist; it uses 1 mm as the reference point and progresses by the fixed ratio of 1:2 in the direction of decreasing size and of 2:1 in the direction of increasing size, such as 0.25, 0.5, 1, 2, 4. See also: Wentworth grade scale. Syn: grade scale.


The group of calcium garnets uvarovite, grossular, andradite, goldmanite, hibschite, kimzeyite, and schorlomite


An isometric mineral, (Ca,Ti,Al,Zr) (sub 2) O (sub 3) ; forms black octahedra in a nepheline syenite near Lake Magad, Tanzania.


A discredited term equal to thomsonite.


A variety of natural asphalt occurring in the Uinta Valley, Utah, as rounded masses of brilliant black solid hydrocarbon. Syn: gilsonite; mineral rubber.


A triclinic mineral, NaCaB (sub 5) O (sub 6) (OH) (sub 6) .5H (sub 2) O ; soft; forms silky white, saline crusts and masses of extremely fine acicular crystals; in saline lake deposits as in Nevada and Chile. Also called cotton ball; boronatrocalcite; natronborocalcite; natroborocalcite.


A triclinic mineral, NiSbS ; cobaltite group; pseudocubic; metallic; steel-gray to silver-white; in veins; a source of nickel. Also called nickel-antimony glance.

Ullrich magnetic separators

These machines have powerful electromagnets in a wedge section. The material is treated on rolls on which magnetism is induced; they consist of alternate disks of soft iron and some nonmagnetic material. The ore is fed over the first roll, which removes the most magnetic material, and the tailings go on to the second, which is weaker, where a second separation is made.


A kind of euvitrain that consists completely of ulmin but that is not precipitated from solution. CF: collain.


The process of peat formation.

ulmin brown

See: Vandyke brown.


a. A maceral of brown coal within the huminite group, consisting of gelified plant-cell walls (ICCP, 1971).

b. A variety of euvitrinite characteristic of ulmain and consisting of gelified but not precipitated plant material. CF: collinite.


A hypabyssal rock composed essentially of large phenocrysts of alkalic feldspar, sodic pyroxene, amphibole, and nepheline with smaller phenocrysts of accessory olivine. Feldspar, pyroxene, and amphibole recur in the groundmass. A porphyritic variety of olivine-bearing phonolite. Syn: uraninite.

ultimate analysis

a. The determination of the elements contained in a compound, as distinguished from proximate analysis, which is the determination of the compounds contained in a mixture.

b. In the case of coal and coke, the determination of carbon and hydrogen in the material, as found in the gaseous products of its complete combustion, the determinations of sulfur, nitrogen, and ash in the material as a whole, and the calculation of oxygen by difference. c. The principal reason for the ultimate analysis of coal is for the classification of coals according to rank, although it is often used for commercial and industrial purposes when it is most desirable to know the sulfur content of coal. Also known as total analysis of coal.

ultimate bearing capacity

The average load per unit of area required to produce failure by rupture of a supporting soil mass. See also: bearing capacity.

ultimate bearing pressure

The pressure under which a foundation will settle with no increase of load. See also: plate bearing test.

ultimate CO (sub 2)

The percent of carbon dioxide that would appear in the flue gases if combustion were perfect. Varies with the fuel.

ultimate compressive strength

That point at which failure by crushing occurs.

ultimate elongation

The percentage of permanent deformation remaining after tensile rupture, measured over an arbitrary length including the section of rupture.

ultimately controlled variable

In mineral processing, the variable whose control is the end purpose of the automatic control system.

ultimate strength

The ultimate strength of a material in tension, compression, or shear, respectively, is the maximum tensile, compressive, or shear stress that the material can sustain, calculated on the basis of the ultimate load and the original or unstrained dimensions. It is implied that the condition of stress represents uniaxial tension, uniaxial compression, or pure shear, as the case may be.

ultimate tensile stress

The load at which a test piece breaks, divided by its original area. See also: tensile strength.


Said of an igneous rock having a silica content lower than that of a basic rock. Percentage limitations are arbitrary; the upper limit was originally set at 44%. The term is frequently used interchangeably with ultramafic. Although most ultrabasic rocks are also ultramafic, there are some exceptions; e.g., monomineralic rocks composed of pyroxenes are ultramafic but are not ultrabasic because of their high silica content. A monomineralic rock composed of anorthite would be considered ultrabasic (SiO (sub 2) = 43.2%) but not ultramafic. Ultrabasic is one subdivision of a widely used system for classifying igneous rocks on the basis of silica content; the other subdivisions are acidic, basic, and intermediate. CF: ultramafic; silicic.


A germanium-bearing variety of diaphorite from Freiberg, Saxony, Germany.


A recently developed process for use in fine-particle flotation. The underlying principle is the use of a finely ground (minus 325-mesh) auxiliary mineral as a carrier for the fine particles to be floated. The fine particles form a slime coating on the carrier mineral; the carrier mineral is then floated, and the fines are piggybacked into the froth.


Said of an igneous rock composed chiefly of mafic minerals, e.g., monomineralic rocks composed of hypersthene, augite, or olivine. CF: hypermelanic; ultrabasic.


Collective name for igneous rocks containing 90% or more mafic minerals; includes picrites, peridotites, and pyroxenites.


A name for synthetic lazurite; extended to related compounds. Also applied to the durable brilliant blue pigment made from its powder. Syn: lapis lazuli.

ultramarine yellow

A lemon-yellow pigment consisting of barium chromate.


Metamorphic processes at the extreme upper range of temperatures and pressures, at which partial to complete fusion of the affected rocks takes place and magma is produced. The term was originated by Holmquist in 1909.


A microscope in which a strong beam of light (Tyndall beam) is viewed at right angles. Individual soluble particles too small to be seen under a normal microscope then appear as bright spots against a dark background. Ultramicroscopy operates below 0.25 mu m.


An ultracrushed variety of mylonite, in which primary structures and porphyroclasts have been obliterated so that the rock becomes homogeneous and dense, with little if any parallel structure. CF: protomylonite; pseudotachylyte. Syn: flinty crush rock.


The supposedly ultrabasic layer of the Earth below the sima, immediately below the Mohorovicic discontinuity.

ultrasonic drilling

A vibration drilling technique that can be used in drilling, cutting, and shaping of hard materials. In this method, ultrasonic vibrations are generated by the compression and extension of a core of electrostrictive or magnetostrictive material in a rapidly alternating electric or magnetic field. The most easily assembled is a magnetostrictive transducer, and the most common magnetostrictive materials, which change in dimension when magnetized, are nickel and vanadium permandur.

ultrasonic inspection

A nondestructive method of testing, based upon the fact that ultrasonic waves are reflected and refracted at the boundaries of a solid medium, from which it is possible to obtain the echoes of a wave transmitted from the surface of a test piece. In addition to being reflected from the boundary of the specimen at which they are directed, the waves are also reflected back by any flaws that lie in the path of the wave. Syn: ultrasonic testing.

ultrasonic testing

See: ultrasonic inspection.

ultrasonic tests

Tests in which high-frequency vibrations (inaudible to a human ear) are used to assist in determining wall thicknesses, pulp densities, etc.


A modification of the use of ultrasonic waves for the detection of internal flaws in metals. By using a persistent screen cathode ray tube and causing the echoes to brighten the trace instead of deflecting it, an ultrasonic image is produced that can be examined and interpreted like a radiograph.


a. Of radiation, beyond the visible spectrum at its violet end; having a wavelength shorter than those of visible light and longer than those of X-rays.

b. Relating to, producing, or employing ultraviolet radiation. CF: visible light.

ultraviolet rays

Electromagnetic waves in the wavelength between visible light rays and X-rays. Ultraviolet light furnishes a quick method of finding and identifying certain metals.


Alkylated monosodium benzene sulfonate, a wetting agent.


See: ulvoespinel.


An isometric mineral, 8[Fe (sub 2) TiO (sub 4) ] ; spinel group; in mafic igneous rocks as fine exsolution lamellae in magnetite. Named for the Ulvoe Islands, Sweden. Syn: ulvite.


A tetragonal mineral, Cu (sub 3) Se (sub 2) ; dark red, tarnishing to violet.


A plow developed from the Anbauhobel machine to allow the conversion of a Lobbe Hobel to give the plow an independent drive.


A brown earth that is darker than ocher and sienna, consisting of iron oxide and oxyhydroxide with manganese oxides, clay, and lime. Highly valued as a permanent pigment, it may be used in its greenish brown natural state (raw umber) or in the dark or reddish brown calcined state (burnt umber). CF: ocher; sienna.


Protective hood over a hoisting cage in a mine shaft.


A monoclinic and orthorhombic mineral, UO (sub 2) MoO (sub 4) .4H (sub 2) O ; black to blue-black; secondary; the only known uranium mineral to contain molybdenum.


An assay made by a third party to settle a difference found in the results of assays made by the purchaser and the seller of ore. See also: control assay.

U.M. plate

Universal mill plate, or plate that is rolled to width by vertical rolls as well as being rolled to thickness by horizontal rolls.


An epidote-rich granite, which also contains pink orthoclase, quartz, also minor opaque oxides, apatite, and zircon. The name is derived from the type locality, the Unaka Range, Great Smoky Mountains, in eastern Tennessee.

unbalanced cutter chain

A cutter chain that carries more picks along the bottom line than the topline. Most chains for cutting at floor level are unbalanced to assist in keeping the jib down. See also: balanced cutter chain.

unbalanced hoisting

The method of hoisting in small one-compartment shafts where only one cage is in operation, as opposed to balanced winding.

unbalanced shothole

A shothole in which the explosive charge breaks down the coal at the back of the machine cut while leaving the front portion standing or in large blocks. This may happen with a deep bottom cut in a thin seam where the vertical distance from the explosive to the inner end of the cut is shorter than the horizontal distance to the exposed face of the seam.


To disengage the drill chuck from the drill stem.

unclassified excavation

Excavation paid for at a fixed price per yard, regardless of whether it is earth or rock.

unconfined compression appliance

A portable appliance for carrying out uniaxial compression tests at a site. Syn: unrestrained compression apparatus.

unconfined compression test

A special condition of a triaxial compression test in which no confining pressure is applied. See also: triaxial compression test; crushing test.

unconfined compressive strength

See: compressive strength.


The quality, state, or condition of being unconformable, such as the relationship of unconformable strata; unconformity. See also: unconformity.


Said of strata or stratification exhibiting the relation of unconformity to the older underlying rocks; not succeeding the underlying rocks in immediate order of age or not fitting together with them as parts of a continuous whole. In the strict sense, the term is applied to younger strata that do not conform in position or that do not have the same dip and strike as those of the immediately underlying rocks. Also, said of the contact between unconformable rocks. CF: conformable. Syn: discordant.


a. A substantial break or gap in the geologic record where a rock unit is overlain by another that is not next in stratigraphic succession, such as an interruption in the continuity of a depositional sequence of sedimentary rocks or a break between eroded igneous rocks and younger sedimentary strata. It results from a change that caused deposition to cease for a considerable span of time, and it normally implies uplift and erosion with loss of the previously formed record.

b. The structural relationship between rock strata in contact, characterized by a lack of continuity in deposition, and corresponding to a period of nondeposition, weathering, or esp. erosion prior to the deposition of the younger beds, and often marked by absence of parallelism between the strata; strictly, the relationship where the younger overlying stratum does not conform to the dip and strike of the older underlying rocks, as shown specif. by an angular unconformity. Syn: unconformability; transgression.

unconsolidated strata

Rocks consisting of loosely coherent or uncemented particles, whether occurring at the surface or at depth.

unconsolidated surface deposits

Surface deposits such as moss, peat, sand, gravel, silt, or mud.

unconventional mineral deposit

A mineral deposit of such unusual grade, mineralogy, or geologic setting that experienced mining personnel would not consider it to be similar to any known deposit type.


Greasy or soapy to the touch, as certain magnesian minerals.


a. A diamond the original shape of which has not been altered artificially.

b. Unadulterated.

undation theory

A theory proposed by Van Bemmelen (1933) that explains the structural and tectonic features of the Earth's crust by vertical upward and downward movements caused by waves that are generated by deep-seated magma.


See: undermanager.

underboom sprays

Sprays located on the rear corners of the shovel at the sides of the continuous miner and aimed towards the front of the gathering arms to suppress dust by wetting the coal.


Rock that remains unbroken inside the neat lines in a tunnel or shaft after firing a round of explosive shots. CF: overbreak.


See: underhand stoping.


Insufficient burden of rock in relation to the explosive charge, resulting in a blown-out shot or a premature shot through shock of a neighboring charge of a blast pattern, often yielding less work than expected.


a. An air crossing in which one airway is deflected to pass under the other.

b. The lower airway of an air crossing. See also: air crossing. c. An undercast is nothing more than an inverted overcast. Undercasts are not considered to be as efficient as overcasts, owing to the tendency of water to collect in them. CF: overcast.

underchain haulage

Haulage in which the chains are placed beneath a mine car at certain intervals with suitable hooks that thrust against the car axle.


A drive is underchained when it incorporates a chain of substantially lower rating than that indicated by normal selection procedures.


a. A layer of fine-grained detrital material, usually clay, lying immediately beneath a coalbed or forming the floor of a coal seam. It represents the old soil in which the plants (from which the coal was formed) were rooted, and it commonly contains fossil roots (esp. of the genus Stigmaria). It is often a fireclay, and some underclays are commercial sources of fireclay. Syn: underearth; seat earth; seat clay; root clay; thill; warrant; coal clay; warrant clay.

b. A bed of clay, in some cases highly siliceous, in many others highly aluminous, occurring immediately beneath a coal seam, and representing the soil in which the trees of the Carboniferous swamp forests were rooted. Stigmarian roots commonly occur as fossils in underclays, many of which are used as fireclays. See also: fireclay.

underclay limestone

A thin, dense, nodular, relatively unfossiliferous fresh-water limestone underlying coal deposits, so named because it is closely related to underclay.


S. Wales. An argillaceous shale forming the floor of many coal seams.

underconsolidated soil deposit

A deposit that is not fully consolidated under the existing overburden pressure. Not yet in equilibrium with existing physical environment. Still being compacted.


A short sluice much wider than the main sluice and set on a steeper grade, generally at right angles to the main sluice. It is designed to save fine gold that does not readily settle. See also: table.


a. To remove a horizontal section of kerf in the bottom of a block of coal to facilitate its fall. See also: underhole; undercutting.

b. To undermine, to hole, or to mine. To cut below or in the lower part of a coalbed by chipping away the coal with a pick or mining machine. Undercutting is usually done on the level of the floor of the mine. See also: cut; undermine. c. A machine cut along floor level in a coal seam to ease its removal by hand, machine, or shotfiring. See also: holding. d. Excavation of ore from beneath a larger block of ore to induce settling under its own weight. e. In stoping, removal either of footwall or of the lower part of a a flattish lode, bed, or seam of ore or coal, thus facilitating detachment of the portion left hanging. Method used in block caving to induce caving in. f. To enlarge a drillhole at a depth that has been previously drilled.

undercut atomizer

A device for passing a fine spray of compressed air and water to dilute the combustible gases and allay the coal dust in the track of a coal-cutter jib. The spray is passed through a modified whale-type jib.

undercut ignition

The ignition of an explosive mixture of combustible gases and air in the undercut of a coal cutter due to frictional sparking. Combustible gases in dangerous quantities often exist in a machine undercut. See also: whale-type jib.

undercut quarry

A quarry in which the walls slant outward (overhang the working face) so as to make the floorspace wider with increasing depth.


a. In salt mining, an electrically driven machine somewhat like a gigantic chain saw. It has a long, thin horizontal bar, about which revolves an endless chain with cutting bits. The most common type is an adaptation of the shortwall coal cutter, a drag-type machine with continuous pick-filled chains to cut at the floor or bottom of the seam. It can make a rapid, continuous cut across the entire width of the face.

b. See: machineman.


a. The process of cutting under the face of a coal seam with a machine so the coal can be shot down readily.

b. A quarrying method intermediate between open pit and adit. Channel cuts, or separations made by wire saws or other means along the quarry walls, are slanted outward; thus, the floorspace is enlarged gradually. Wings or buttresses of stone may be left at intervals for wall support. c. The making of a cut, by hand or coal cutter, along the floor level in a coal seam to ease its working by hand or breaking by explosive. See also: undercut; floor cut; holing.

undercutting machine

An electrically driven machine used to make a cut about 10 ft (3.0 m) deep near the bottom of a coalbed.

undercutting of old workings

A method of mining a vein that has been worked out above and in which the shaft is further sunk, with a crosscut being made to the vein at a depth below the previous workings.


Drilling below the theoretical blasting bottom. Syn: subdrilling.


A hard fireclay forming the floor of a coal seam. See: underclay.

underedge stone

The material that forms the floor of an ironstone mine.


To advance a diamond or other type of rock-drilling bit into rock at a lesser rate than that warranted by the condition of the rock and/or the condition of the bit.

underfeed stoker

A mechanical stoker suitable for small boilers, such as the vertical, water-tube, and locomotive types. Coal is conveyed direct from a bunker or hopper by a feed worm, which forces the fuel up through the bottom of the retort in which it is burned. Volatiles driven off must pass through the ignited fuel, thus eliminating smoke. An underfeed stoker operates most successfully on graded coals with an upper size limit of 1 to 2 in (2.5 to 5.1 cm). See also: stoker; vibrating grate.


a. In ceramics, to fire (as brick) insufficiently.

b. To fire from beneath.


The oversize material leaving a classifier.

underground bunker

a. Arrangements, such as high-capacity supplementary conveyors, staple pits, hoppers, or standage room for cars, positioned at key points between the faces and pit bottom. The object is to enable costly power-loading machines to operate continuously when there are surface or shaft delays. See also: bunker conveyor; gate road bunker.

b. A large-capacity hopper to absorb peak deliveries and provide an even rate of feed to main transport systems, or winding shaft. See also: bunker.

underground cable

A single or multiple conductor cable sheathed in lead or other waterproof materials, carried in a duct beneath the surface of the ground.

underground coal gasification

See: underground gasification.

underground connections

Mines or areas that are connected underground shall be considered as a single mine if the underground connections between previously separate mines or areas subject the workers in the respective mines or areas to a reasonable likelihood of danger from mine fires or the products of fires, explosions or the forces and products of explosions, mine inundations, or personnel accidents.

underground dam

Seal against water or spread of fire.

underground exploration

a. The driving of advance exploring headings and up-and-down boring to establish the continuity and thickness of coal seams or other mineral deposits. See also: exploratory drilling.

b. Extensions of a known ore deposit may be probed along its strike or dip in which shafts, drifts, or crosscuts may be driven. A study of the habits of known ore shoots, by mapping, surveying, and sampling, is a desirable preliminary to underground exploration.

underground fires

There are two types of underground fires: (1) those that involve exposed surfaces and are known as open, freely burning fires and (2) those that may be wholly or partly concealed and are invariably caused by spontaneous heating of the coal itself, known as gob fires.

underground garage

See: locomotive garage.

underground gasification

A method of burning the coal in place to produce a combustible gas that can be burned to generate power or processed into chemicals and fuels. Air and/or steam is blown underground to support the controlled combustion in the coal seam. The resultant gaseous mixture is a low-heating-value fuel gas. See also: blind borehole process. Syn: underground coal gasification.

underground geology

Usually implies direct evidence derived from shafts, wells, and borings, or obtained by geophysical methods. Also called subsurface geology.

underground glory-hole method

A method used in large deposits with a very strong roof. In this method, a deposit is divided by levels and on every level chutes are raised to the next one. Mining starts from the mouth of the chutes in such a way as to develop a funnel-shaped excavation (mill, glory) with slopes so steep that the broken ore falls into the chutes and thus to the cars on the lower level. A sufficiently strong pillar is left for protection at the higher level. Syn: underground milling.

underground haulage

The transportation of coal or minerals from the working face to the shaft bottom. Haulage usually implies trams, tubs, or mine cars drawn by horses, locomotives, electric or compressed-air haulage engines. Conveyors are not generally regarded as a haulage method. See also: gravity haulage; haulage; locomotive haulage; main transport; subsidiary transport.

underground milling

See: underhand stoping; underground glory-hole method.

underground mine conveyor

Sectional conveyor, usually of the troughed belt type, capable of being lengthened or shortened as mining operations advance or retreat, as contrasted to an above-ground conveyor having a fixed length for reasonably permanent installation. According to location in the mine or usage, underground conveyors may be known as face, room, gathering, main haulage, or intermediate haulage conveyors. See also: belt conveyor; conveyor; haulage conveyor; flight conveyor; mother conveyor. Syn: main conveyor; entry conveyor.

underground opening

Natural or manmade excavation under the surface of the Earth.

underground ore bin

See: measuring chute.

underground shaft

A shaft sunk from an adit, tunnel, or working level, through which mining operations are conducted. The upper end terminates underground. A winze or raise becomes an underground shaft when equipped and used for hoisting and the conduct of other mining operations. CF: winze.

underground station

a. An enlargement of an entry, drift, or level at a shaft at which cages stop to receive and discharge cars, workers, and material.

b. An underground station is any location where stationary electric equipment is installed for the utilization of electricity. This includes pump rooms, compressor rooms, hoist rooms, battery-charging rooms, etc. c. Excavation housing special equipment.

underground surveying

Distinctive features of underground surveying are that stations are usually in the roof instead of the floor; the object to be sighted and the crosshairs of the telescope must be illuminated; distances are usually measured on the slope; either the transit tripod has adjustable legs or a trivet is used; and often an auxiliary telescope is attached to the transit, either at one end of the horizontal axis or above the main telescope, with the line of sight of the auxiliary telescope parallel to that of the main telescope. Horizontal and vertical distances are computed from slope distances and vertical angles. The transit is set up at one station, being centered by plumb, and the vertical distance from the station to the horizontal axis of the transit is measured. A plumb bob is hung at the next station, with a point on the plumbline marked by some form of clamping target. The vertical angle to the point so marked is measured, and the distance from horizontal axis to the target is taped.

underground transformer

A flameproof, air-filled transformer of a size up to 300 kV.A, which can be used inby near the face in safety-lamp mines. A nitrogen-filled transformer for mining use is the latest trend.

underground transportation

The transporting of ore, rock, people, materials, and supplies through shafts and haulageways, including the loading of ore or rock into cars and carrying it to the surface.

underground water

See: ground water; subsurface water.

underground workshop

An underground room prepared at an accessible spot in an underground mine in which repairs can be made on the mining equipment used underground.

underhand longwall

Underground mining technique based on underhand stoping and cut-and-fill stoping with a single advancing face. See also: underhand stoping; cut-and-fill stoping.

underhand stope

A stope made by working downward from a level.

underhand stoping

The working of a block of ore from an upper to a lower level; mining downward. The method is particularly suitable for narrow, highly inclined deposits. Syn: horizontal-cut underhand; underbreaking; underground milling. CF: overhand stoping. See also: underhand longwall.

underhand vertical slice

See: square-set stoping.

underhand work

Picking or drilling downward.


a. To cut away or mine out the lower portion of a coal seam or a part of the underclay so as to win or get the overlying coal.

b. To mine out a portion of the bottom of a seam, by pick or powder, thus leaving the top unsupported and ready to be blown down by shots, broken down by wedges, or mined with a pick or bar. In England, the terms jad, hole, undercut, kirve, and bench are synonymous. See also: undermine; undercut.


The extension of a vein or ore deposit beneath the surface; also, the inclination of a vein or ore deposit from the vertical; i.e., hade. Syn: underlie. See also: hade.

underlay shaft

a. A shaft sunk in the footwall and following the dip of a vein. Also called underlier.

b. Shaft that slopes at the dip angle of a lode, but is carried below the ore. Also called a footwall shaft. See also: incline shaft.


A development level or drift, driven from the surface, in ironstone mining.


a. The angle at which stulls or posts are set between walls. The setting angle is slightly steeper than the perpendicular to the vein, and the post thus tightens with the downward settlement of the hanging wall.

b. To lie or be situated under, to occupy a lower position than, or to pass beneath. The term is usually applied to certain rocks over which younger rocks (usually sedimentary or volcanic) are spread out. Ant: overlie. Syn: underlay.


Insufficient charging of a ball mill for proper grinding of enamel slip.


Lying under or beneath; fundamental. See also: seat earth.

underlying beds

The rocks situated under a deposit or other strata.


In Great Britain, the underground mining engineer and senior executive official. Everything that has to do with the underground must be subject to his or her control, esp. regarding safety and health of personnel. Also called underlooker. Syn: under.


To excavate the earth beneath, esp. for the purpose of causing to fall; form a mine under. See also: undercut; underhole.


a. Building up the wall of a mine shaft to join that above it.

b. The act of supporting a superior part of a wall, etc., by introducing a support beneath it.

underpoled copper

To reduce to metal the cuprous oxide from blister copper produced in a converter, green poles are pushed into the molten material to bring the percentage of dissolved oxygen below 0.5. If this reaction (which results in flat-topped ingots having a smooth fracture) is incomplete, the ingot fractures too readily and has a darker color. This shows it to have been insufficiently reduced, or underpoled. See also: tough pitch.


To enlarge or ream a borehole below the casing. See also: underreaming.


A tool or device having cutters that can be expanded or contracted by mechanical or hydraulic means and used to enlarge or ream a borehole below the casing or drivepipe. Also called expansion bit; expansion reamer. See also: hydraulic underreamer; underreamer bit.

underreamer bit

The assembled device consisting of the lugs or jaws attached to an expanding mechanism used to enlarge or ream a borehole below a string of casing. See also: underreamer.

underreamer cutter

See: underreamer lug.

underreamer lug

A diamond set or other type of expansible or contractable jaw on an underreamer bit. Syn: underreamer cutter. See also: cutter.


a. The widening out of the foot of a bored hole or of certain types of foundation piers to increase the load-bearing area.

b. See also: underream.

underreaming bit

An expanding bit used to enlarge the diameter of the hole below the casing to allow the casing to be lowered farther down the borehole.

underrope haulage

An endless rope haulage in which the ropes run under the cars. The cars are attached singly or in short sets by clips. See also: overrope haulage.


a. Said of an igneous rock consisting of unsaturated minerals; e.g., feldspathoids and olivine.

b. Said of a rock whose norm contains feldspathoids and olivine, or olivine and hypersthene. CF: unsaturated; saturated; saturated rock.

underscreen water

Water that is fed into the cells of a washbox below the level of the screen plate.

undersea prospecting

The driving of exploring headings seaward from landside mine workings combined with up-and-down boring to establish higher or lower seams. Also, a technique developed by the National Coal Board, Great Britain, for exploration drilling from a tower that can be floated out to sea and grounded on the seabed.

undersea workings

See: submarine mines.

undershot wheel

a. A vertical waterwheel into the circumference of which are set blades that are pushed by water passing underneath.

b. A waterwheel used for low heads, in which the power is obtained almost entirely from the impulse of the water on the vanes.


a. Particles in a screen overflow that are smaller than the normal dimensions of the screen apertures.

b. The smaller of two classified products. In the case of ore pulp or fine coal, the undersize is the overflow and the oversize is the underflow. See also: classifier. c. A drill hole that is not to size because of gage loss on the bit and/or the reaming shell with which it was drilled. d. A bit or reaming shell, the diametric dimensions of which are less than specified as standard. e. That part of a crushed material that passes through a screen. f. Material in a product of size smaller than the reference size; may be expressed as a percentage of the product.

undersize control screen

A screen used for the removal of undersize from a product.

undersize core

Core the outside diameter of which is less than standard.


A low-angle reverse fault resulting from the sliding of the footwall beneath a relatively passive hanging wall. CF: overthrust.


The seaward return flow, near the bottom of a sloping beach, of water that was carried onto the shore by waves. CF: rip current.

undertub system

The endless-rope system generally used on moderate and constant gradients where the floor is good. In this system, the rope runs underneath the tubs or cars in the center of the rails. Curves are negotiated by a series of small vertical pulleys between the rails and are best of large radius. Clips are generally preferred to lashing chains, and the system suits automatic clipping and unclipping. CF: overtub system.

undervoltage relays

Like undercurrent relays, undervoltage relays indicate when voltage is not up to the level it should be. Undervoltage values result in the breaker tripping and staying out until the undesirable condition is corrected.


a. The weight of that portion of the strata overlying a coal seam at the face, which is supported by the timber or steel props. See also: nether roof; overarching weight; traveling weight.

b. A diamond bit, the crown of which is inset with diamonds so widely spaced that part of the crown is without cutting points and the bit cannot be made to cut.


A rope or cable wound and attached so that it stretches from the bottom of a drum to the load.

undeveloped land

Land remaining in its natural state, not disturbed by mineral exploration or extraction activities.

undiscovered resources

Resources, the existence of which are only postulated, comprising deposits that are separate from identified resources. Undiscovered resources may be postulated in deposits of such grade and physical location as to render them economic, marginally economic, or subeconomic. To reflect varying degrees of geologic certainty, undiscovered resources may be divided into hypothetical resources and speculative resources.

undisturbed sample

A sample that is as undisturbed as humanly possible, as distinct from a sample disturbed by boring tools. Special appliances are used to obtain such samples from boreholes, and the material is preserved in its natural state in airtight containers. Undisturbed samples are required so that the in-place (in situ) properties of the soil may be determined. It is difficult to obtain undisturbed samples of sandy soils without considerable preparation. See also: soil core.

undulatory extinction

In polarized-light microscopy, said of a mineral that fails to go extinct as a unit under crossed polars, but exhibits waves of extinction sweeping across the grain upon rotation of the microscope stage. Syn: wavy extinction. CF: extinction; zoning.

unequal angle

A metal angle section with two legs of unequal length.

uneven fracture

A general type of mineral breakage that produces rough and irregular surfaces. CF: fracture.

unfaced quartz

A name given to defaced masses of raw quartz used in the oscillator industry.


A trigonal mineral, K (sub 3) Na (sub 8) Fe(SO (sub 4) ) (sub 6) (NO (sub 3) ) (sub 2) .6H (sub 2) O ; in thick, tabular rhombohedral crystals; at Chuquicamata, Chile.


Unworked rock of any kind.


In optical crystallography, those anisotropic crystals having one direction of apparent isotropy, i.e., one optic axis, corresponding to the unique direction of axial symmetry in the hexagonal, trigonal, and tetragonal crystal systems. Uniaxial crystals are positive if their extreme refractive index (extraordinary ray) is less than their axial refractive index (ordinary ray), negative if greater. CF: isotropic; isotropy; anisotropy; biaxial.

uniaxial stone

One that has crystallized in the tetragonal, trigonal, or hexagonal crystal system and, therefore, has only one direction or axis of single refraction. CF: biaxial stone.


An obsolete syn. of monocline. CF: anticlinal bend.

unidimensional consolidation

A test in which the volume change in a soil sample is observed when subjected to increasing increments of load. A soil sample, which may be 3 in (7.6 cm) in diameter and 0.8 in (2 cm) thick, is compressed between two porous stones, and the movement under load is noted.

unidirectional ventilation

a. A form of air travel; the air enters at one point, passes through the workings, and goes out at a distant point. Recirculation is impossible where unidirectional ventilation is used; thus the mine is safer than with recirculated air.

b. Ventilation in which air in adjacent openings flows in the same direction and is entirely fresh or exhaust air.


The fundamental principle or doctrine that geologic processes and natural laws now operating to modify the Earth's crust have acted in the same regular manner and with essentially the same intensity throughout geologic time, and that past geologic events can be explained by phenomena and forces observable today; the classical concept that the present is the key to the past. The doctrine does not imply that all change is at a uniform rate and does not exclude minor local catastrophes. Syn: principle of uniformity.

uniformity coefficient

An expression of variety in sizes of grains that constitute a granular material.


A low-density nitroglycerin powder type of equivalent sheathed explosive.

unilateral transducer

A transducer that cannot be actuated at its outputs by waves in such a manner as to supply related waves at its inputs.


a. State of a substance that has dissolved without dissociating into ions; solute retaining its compounded state.

b. State of a substance (in solid, gaseous, or liquid state) with atoms that have neither an excess nor a deficiency of electrons, so that they have no net charges.

union shop

A shop or mine run according to the requirements of a trade union. CF: open shop.

unique diameter

A direction in a crystal parallel to the highest symmetry axis; i.e., the c axis in trigonal, tetragonal, and hexagonal systems; the three reference axes in the orthorhombic system; and the b (or c in the first setting) axis in the monoclinic system.


Smelter contracts make frequent use of the work unit. A unit means 1%. Since a short ton contains 2,000 lb (907.2 kg), a unit is equivalent to 20 lb/t (10.0 kg/t) of ore.

unit cell

A parallelepiped unit of atomic dimensions within a crystal structure, containing all the atoms in the chemical unit in definite, fixed positions; and all the symmetry elements of the space lattice from which the whole crystal or crystal structure is built by regular repetitions of this unit in three dimensions. CF: asymmetric unit.

unit coal

a. Applied to prepared coal as for analysis, and being the pure coal substance considered altogether apart from extraneous or adventitious material (moisture and mineral impurities), which may by accident or through natural causes have become associated with the combustible organic substance of the coal.

b. The pure or actual coal substance as derived from taking into consideration the corrected ash. The differentiation between the noncoal substance of a sample being analyzed and the coal itself. It is expressed by the formula: Unit coal = 1.00 - (W + 1.08 A + 0.55 S), where W = water, A = ash, and S = sulfur.

united veins

Where two or more veins unite, the oldest or prior location takes the vein below the point of union, including all the space of intersection.

unit operation

Recognition, study, application, and control of the principles and factors utilized in a distinct and self-contained process (for example, filtration). This avoids the duplication of effort that attends study of filtration of oil, sugar, ore pulp, etc., as though each involved a unique set of principles.

unit pressures

The total pressure divided by the number of area units on which the load is imposed, such as the diamonds in a diamond-bit crown, usually expressed as pounds per square inch, tons per square foot, pounds per diamond, etc.

unit process

Distinct and self-contained operations that can be studied individually. In mineral processing, unit processes include crushing, grinding, classification, gravity treatment, pulp conditioning, flotation, thickening, leaching, and filtration.

unit retardation plate

See: selenite plate.

unit strain

Unit tensile strain is the elongation per unit length; unit compressive strain is the shortening per unit length; unit shear strain is the change in angle (radians) between two lines originally at right angles to each other.

unit stress

The stress or load per unit of area, usually taken per square inch of section. For instance, if a bar is 1 in by 2 in (2.5 cm by 5.1 cm) in section, the unit stress of the bar will be 1,000 divided by 2 (sectional area) or 500 psi (3.4475 MPa).

unit train

A system delivering coal more efficiently in which a string of cars, with distinctive markings, and loaded to "full visible capacity," is operated without service frills or stops along the way for cars to be cut in and out, from the loading place to the point of delivery.

unit value

The monetary value of a mineral or rock product per ton or other unit of measurement. See also: value.

unit ventilation

A system of ventilation in which each working face is ventilated by a separate air current.

unit weight

a. Weight per unit of volume. See also: dry unit weight; effective unit weight; maximum unit weight; saturated unit weight; submerged unit weight; unit weight of water; wet unit weight; zero air voids unit weight.

b. The density of a material. See also: density.

unit weight of water

The weight per unit volume of water; normally equal to 62.4 lb/ft (super 3) or 1 g/cm (super 3) . See also: unit weight.


a. Having a valence of one.

b. Having one valence; e.g., calcium, which has only a valence of two.

universal arc-shearing machine

A machine with a rotating jib head so that vertical or shearing cuts can be made in addition to the arc wall cut. An arcwall machine will cut a 12-ft (3.7-m) heading to a depth of 6 ft (1.8 m) in 10 min.

universal clamp

A clamping device used on a drill column by means of which a horizontal arm can be affixed at any point on the vertical section of a drill column.

universal coal cutter

A coal cutter with a jib capable of cutting at any height or angle. It may be mounted on crawler tracks. See also: universal machine; turret coal cutter.

universal coupling

Coupling that joins two driving shafts that rotate about differently slanted axes.

universal gas mask

Designed as an all-purpose mask for protection against a great variety of toxic gases, vapors, and smokes, including carbon monoxide. It is equipped with an indicator that shows at a glance the remaining service time of the canister for carbon monoxide. This mask is particularly effective for mines, fire fighting, and general industrial uses where the contaminants are of relatively low content.

universal-joint couplings

These couplings are used where shafts intersect at any angle or where pivoted members must be driven. If there is an offset in the two shafts, or if one or both shafts must change location during operation, two of these couplings are used, and one is fitted with a splined joint mating with the connecting intermediate shaft to allow axial movement.

universal lay rope

See: lang lay rope.

universal machine

A power-driven coal cutter that will not only cut horizontal kerfs, but will also cut vertical kerfs at any angle, and is designed for operation either on track, crawler treads, or rubber tires. Syn: universal coal cutter; arc shear machine.

universal motor

An electric motor rated at less than 1 hp (746 W) output that operates on either direct or alternating current.

universal pH indicator

Mixture of several indicator dyes, each of which changes color through a specific pH range, so that by suitably combining a wide color change and pH, a reading can be obtained.

universal plant indicator

Indicator plant that is restricted exclusively to rocks or soils of a definite mineral content and not found under any other conditions. CF: local indicator plant.

universal stage

A stage of three, four, or five axes of rotation, attached to the rotating stage of a polarized-light microscope, that enables a thin section or mineral grain under study to be turned in a precisely controlled fashion about three mutually orthogonal axes. It is used to determine precisely the optical properties and parameters of minerals or their orientation in a set of external coordinates. Syn: U-stage; Federov stage. CF: goniometer; spindle stage.

universal testing machine

An instrument so designed that it is capable of exerting a tensile, compressive, or transverse stress on a specimen under test. Further, it can be adapted for the determination of Brinell hardness, ductility, cold bend, and other properties. The machine consists essentially of three systems: loading, weighing, and indicating, the loading being applied either mechanically or hydraulically.

universal train

A roll train having adjustable horizontal and vertical rolls, so as to produce sections of various sizes.


In attacking a rock face, the first effort of the miner is directed toward making a cut that will permit the succeeding shots to exert the greatest force with the minimum charge of explosive. In doing this unkeying, the miner takes advantage of any persistent seam in the rock face.

unlimited pump

A deep-well pump operated from the level of the ground above.


A machine that unloads iron ore from boats and cars, by power, generally electric.

unloading conveyor

Any of several types of portable conveyors adapted for unloading bulk materials, packages, or objects from conveyances. See also: portable conveyor.

unloading trough

A short section of trough, designed for insertion in a standard shaker trough, which will allow the coal to be unloaded at that point by being diverted to either side by the unloading trough. C-clamps are used to hold the unloading section in place.


See: liberation.


Proprietary flotation collector agent based on emulsified tall oil, fuel oil, and water-soluble aryl-alkyl sulfonate used to treat hematite ores.


See: exsolution.


a. Said of a rock specimen whose original position in space, when collected, is unknown.

b. Said of a rock fabric that shows no ordered spatial arrangement. CF: preferred orientation. c. Said of a map or surveying instrument whose internal coordinates are not coincident with corresponding directions in space.

unpatented claim

a. Mining claim to which a deed from the U.S. Government has not been received. A claim is subject to annual assessment work, to maintain ownership.

b. A claim that requires $100 of work to be done each year. A claim cannot be patented until $500 has been spent on it. c. A mining claim for which the holder has no patent. Under the Multiple Surface Use Act of 1955, discoveries of common varieties of sand, stone, gravel, pumice, cinders, and clay cannot be located as mining claims; however, it does not affect the validity of a discovery in these materials based on the presence of other valuable minerals.

unproductive development

The drifts, tunnels, and crosscuts driven in stone, preparatory to opening out production faces in a coal seam or orebody. Horizon mining is characterized by a heavy outlay on the initial unproductive development. See also: dead work; in-the-seam mining; productive development.

unproven area

An area in which it has not been established by drilling operations whether oil and/or gas may be found in commercial quantities.

unreserved mineral

A mineral that belongs to the owner of the land on which or in which it is located. The owner of the land is its exclusive owner and can deal with it freely. Examples include limestone, dolomite, barite, fluorite, fireclay, plastic clay, glass sand, marble, and gypsum.

unrestrained compression apparatus

See: unconfined compression appliance.

unripe diamond

See: rock crystal.


a. Applied to minerals that are incapable of crystallizing from rock magmas in the presence of an excess of silica. Such minerals are said to be unsaturated with regard to silica and include feldspathoids, analcime, magnesian olivine, melanite, pyrope, perovskite corundum, calcite, and perhaps spinel. CF: undersaturated; saturated rock.

b. Applied to air that contains less water vapor than the maximum or saturation content for the conditions pertaining.

unscreened coal

a. Coal for which no size limits are specified.

b. Aust. Run-of-mine coal.


The recovery of a sealed-off mine area that had been sealed to extinguish a fire. Two general systems may be employed: (1) recovering the fire area in successive blocks by means of air locks, and (2) reventilation of the fire area after there is conclusive evidence that the fire has been extinguished. See also: sealed area.


The act or process of removing soil, as in opening a quarry.


a. A quarry term that refers to all cracks or lines of weakness, other than bedding planes, that may cause rock to break before or during the process of manufacture. Various types of unsoundness are known locally as joints, headers, cutters, hairlines, slicks, seams, slick seams, dry sewns, dries, and cracks.

b. The condition of a solid metal that contains blowholes or pinholes due to gases, or cavities resulting from the liquid-to-solid contraction (that is, contraction cavities). See also: gas evolution.


a. Said of a constituent of a sedimentary rock that does not effectively resist further mineralogic change and that represents a product of rapid erosion and deposition (as in a region of tectonic activity and high relief); e.g., feldspar, pyroxene, hornblende, and various fine-grained rock fragments.

b. Said of an immature sedimentary rock (such as graywacke) consisting of unstable particles that are angular to subrounded, poorly to moderately sorted, and composed of feldspar grains or rock fragments. CF: labile. c. Said of a radioactive substance. CF: stable.

unstable isotope

See: radioisotope.

unstable relict

A relict that is unstable under newly imposed conditions of metamorphism, but persists in a perhaps altered but still recognizable form owing to the low velocity of transformation. A preferable term would be metastable relict. CF: stable relict. See also: armored relict.


Not formed or deposited in strata; specif. said of massive rocks or sediments with an absence of layering, such as granite or glacial till.


Pumping or draining the water from mines. CF: dewatering.


See: fresh.