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

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deoxidized copper

Copper from which cuprous oxide has been removed by adding a deoxidizer, such as phosphorus, to the molten bath.


a. The removal of oxygen from molten metals by use of suitable deoxidizers.

b. Sometimes refers to the removal of undesirable elements other than oxygen by the introduction of elements or compounds that readily react with them. c. In metal finishing, the removal of oxide films from metal surfaces by chemical or electrochemical reaction.

dependent shot

A charge of explosives in a borehole that depends for its effect upon the result of one or more previously fired shots.


Elimination of phosphorus from steel, in basic steelmaking processes. Accomplished by forming a slag rich in lime. See also: acid process; basic process; Bessemer process; open-hearth process.


Removal of part or all of residual phosphorus from steel in basic smelting.

depleted fuel

See: spent fuel.


The act of emptying, reducing, or exhausting, as the depletion of natural resources. In mining, specif. said of ore reserves. See also: economic depletion.

depletion allowance

A proportion of income derived from mining or oil production that is considered to be a return of capital not subject to income tax.


An area or site of maximum deposition; the thickest part of any specified stratigraphic unit in a depositional basin.


a. Anything laid down. Formerly applied only to matter left by the agency of water, but now includes mineral matter in any form that is precipitated by chemical or other agent, as the ores in veins.

b. Mineral deposit or ore deposit is used to designate a natural occurrence of a useful mineral, or an ore, in sufficient extent and degree of concentration to invite exploitation. c. Earth material of any type, either consolidated or unconsolidated, that has accumulated by some natural process or agent. The term originally applied to material left by water, but it has been broadened to include matter accumulated by wind, ice, volcanoes, and other agents. CF: sediment. d. An informal term for an accumulation of ore or other valuable earth material of any origin. e. Verb. To lay down or let drop by a natural process; to become precipitated.


a. The process of natural accumulation of rock material thrown down or collected in strata by water, wind, or volcanic action; also, the material thus deposited. Opposite of denudation.

b. The precipitation of mineral matter from solution, as the deposition of agate, vein quartz, etc.

deposit type

A class representing all the recognized mineral deposits that are defined by physical and genetic factors that can be consistently differentiated from those of other classes or deposit types.


In the froth flotation process, a reagent that reacts with a particle surface to render it less prone to stay in the froth, thus causing it to wet down as a tailing product. Depressants act by complexing elements at surface lattices of minerals that might carry a charge attractive to conditioning agents; by destroying collector coating; by surface modification of particles. See also: bathotonic reagent; surface activity.

depressed water level

The lowest level of ground water during drainage or pumping.


a. Any relatively sunken part of the Earth's surface; esp. a low-lying area surrounded by higher ground and having no natural outlet for surface drainage, as an interior basin or a karstic sinkhole.

b. A structurally low area in the crust, produced by negative movements that sink or downthrust the rocks. CF: basin; uplift.

depression contour

A closed contour, inside of which the ground or geologic structure is at a lower elevation than that outside, and distinguished on a map from other contour lines by hachures marked on the downslope or downdip side.


A substance (usually inorganic) that inhibits flotation of the mineral. CF: activator.


S. Afr. The word alone generally denotes vertical depth below the surface. In the case of incline shafts and boreholes, it may mean the distance reached from the beginning of the shaft or hole, the borehole depth, or inclined depth.

depth contour

See: isobath.

depth indicator

A dial or other appliance on a winding apparatus that indicates to the person in charge the position of the cage in the shaft. The indicator must be in addition to any mark on the rope or drum. See also: visual indicator.

depth marker

A small metal tag or wooden block placed in the core box at the bottom of the core recovered from each run, on which is marked the depth at which the core was cut in the borehole.

depth of cut

The thickness of material removed from the workpiece in a single pass.

depth of focus

Depth of an earthquake or explosion below the Earth's surface.

depth of soil exploration

Soil sampling is usually carried down to include all deposits likely to have a bearing on the stability of mine structures. Shear tests are made in each bed below the foundation to a depth of at least 1 - 1/2 times the breadth of the foundations. See also: site investigation.

depth of stratum

The vertical distance from the surface of the Earth to a stratum.

depth per bit

The length of borehole that can be drilled with a steel bit until it must be resharpened.

depth point

In seismic work, a position at which a depth determination of a mapped horizon has been calculated.


a. An underground official in a mine of coal, stratified ironstone, shale, or fire clay, with statutory responsibility for the safe and proper working of a district of the mine. Also called examiner; fireman (undesirable usage). See also: fireman.

b. Within limits, the deputy is also in charge of the workers in the district. c. Eng. In Northumberland and Durham, the person who sets timbers or props in a coal mine is sometimes called a deputy. d. N. of Eng. A junior official responsible for safety precautions and mining operations in a face district. e. N. of Eng. A person who fixes and withdraws the timber supporting the roof of a mine, attends to the safety of the roof and sides, builds stopping, puts up bratticing, and looks after the safety of the miners. f. Eng. In the Midland coalfield, an underground official who looks after the general safety of a certain number of stalls (rooms) or of a district, the deputy does not set timber but verifies that it is properly done. g. A mine boss.

deputy surveyor

A person appointed by the Surveyor General of the United States to make proper surveys of lode or placer mining claims, prior to the issuing of a patent.


A safety device for derailing mine cars, usually installed on grades to protect miners working below. See also: drop log.

derailing drag

See: backstay.

derail unit

This device locks to rails to derail cars. Wedge construction eliminates spiking. It protects workers in railroads and mines against wild cars, switching cars, or sudden car movement. Some types are equipped with a warning flag.


A monoclinic mineral, (Fe,Ti) (sub 7) SbO (sub 13) (OH) ; forms minute prismatic crystals or twins.

Derbyshire spar

Fluorite, found abundantly in Derbyshire, England. See also: fluorspar. Syn: Derby spar.

Derby spar

A popular name for fluorite in Derbyshire, England. Syn: Derbyshire spar.


An amethyst-colored variety of fluorite.

derivative rock

A rock composed of materials derived from the weathering of older rocks; a sedimentary rock, or a rock formed of material that has not been in a state of fusion immediately before its accumulation.

derivative structure

Representation of crystal structures in terms of a master structure, e.g., feldspar as derivative of coesite with aluminum replacing tetrahedral silicon and charge balance maintained by intertetrahedral alkali and alkali-earth ions.

derived fossil

A fossil that is not native to the rock in which it is found, e.g., a fossil found as a pebble in a conglomerate.

derived fuel

A fuel obtained from a raw fuel by some process of preparation for use, for example, coke, charcoal, benzene, and gasoline.


A skin disease caused by the application of dust or liquids. In coal mining, the dusts may be coal or stone dust and the liquids may be mine waters, oil or grease, perspiration and acids or alkalis. The majority of cases occur in deep and hot mines having high wet-bulb temperatures.


a. The framed wood or steel tower placed over a borehole to support the drilling tools for hoisting and pulling drill rods, casing, or pipe. Sometimes incorrectly called a tower.

b. The framework over a borehole, used primarily to allow lengths of drill rod to be added to the drilling column. c. A three- (or more) legged framework for supporting drill rods and tackle in deep boring; a temporary three-legged headframe, or headgear, for a shaft.

derrick crane

A crane in which the top of the post is supported by fixed stays in the rear and the jib is pivoted like the boom of a derrick. See also: derricking jib crane.

derricking jib crane

A jib crane in which the inclination of the jib, and hence the radius of action, can be varied by shortening or lengthening the tie ropes between the post and the jib.

derrick rope

The rope used for supporting and hoisting the boom on jib cranes and excavators.


Any process for making potable water from sea water or other saline waters. Distillation is the oldest method. Others involve electrodialysis, freezing, extraction, and ion exchange. Also called desalination.

descensional ventilation

A ventilation system in which the downcast air is conducted to the top end of the workings (in inclined workings) and it then flows downhill from level to level. In deep mines, the system helps to keep the faces cool. See also: ascensional ventilation; homotropal ventilation; antitropal ventilation.

descension theory

A theory of formation of supergene mineral deposits involving the descent from above of mineral-bearing solutions. The theory originated with the Neptunian school of thought of the 18th century, which postulated an aqueous origin for all rocks. CF: ascension theory.


a. An orthorhombic mineral, 4[PbZn(VO (sub 4) )(OH)] having Zn replaced by Cu toward mottramite; greasy; varicolored; in oxidized zones of ore deposits; a source of vanadium. Syn: vanadite.

b. The mineral group arsendescloizite, cechite, descloizite, mottramite, and pyrobelonite.

descriptive gemology

The classification, composition, properties, trade grades, sources, and the methods of recovery, fashioning, and use of gem minerals and gem materials and their substitutes. See also: gemology.

descriptive mineralogy

That branch of mineralogy devoted to the description of the physical and chemical properties of minerals.


Removal by chipping of surface blemishes from ingots or blooms.

desert crust

a. A hard layer, containing calcium carbonate, gypsum, or other binding matter, exposed at the surface in a desert region.

b. Desert varnish. c. Desert pavement.

desert glass

See: obsidian; moldavite.

desert lands

All lands exclusive of timber lands and mineral lands that will not, without irrigation, produce some agricultural crop.

desert pavement

A natural residual concentration of wind-polished pebbles, boulders, and other rock fragments, mantling a desert surface where wind action and sheetwash have removed all smaller particles, and usually protecting the underlying finer-grained material from further deflation. The fragments commonly are cemented by mineral matter. Syn: desert crust. See also: lag gravel.

desert rat

In the Western United States, a prospector, esp. one who works and lives in the desert, or who has spent much time in arid regions. The name is derived from a small rodent common throughout much of the Great Basin and Southwestern United States.

desert rose

A radially symmetrical group of crystals with a fancied resemblance to a rose, formed in sand, soft sandstone, or clay. These crystals are commonly calcite, less commonly barite, gypsum, or celestine.

desert varnish

A thin dark shiny film or coating, composed of iron oxide accompanied by traces of manganese oxide and silica, formed on the surfaces of pebbles, boulders, and other rock fragments in desert regions after long exposure, as well as on ledges and other rock outcrops. It is believed to be caused by exudation of mineralized solutions from within and deposition by evaporation on the surface. See also: patina.


A substance having an affinity for water. Used for drying purposes.


To dry; to remove moisture; to preserve by drying.


A drying out, as in loss of water from sediments, or evaporation from water bodies in arid regions, producing evaporites.

desiccation crack

See: mud crack.


A short glass jar fitted with an airtight cover and containing some desiccating substance (as calcium chloride), above which is placed the material to be dried or to be protected from moisture.


A type of diamond-drill fitting that, when standardized, has specific dimensions and thread characteristics establishing interchangeability of parts made by different manufacturers, and size by specific dimension of the set core-bit inside diameter. Design characteristics supplement the group characteristics that provide for integration of ranges. The design characteristics of drill fittings are established by the second letter in two-letter names and by the third letter in three-letter names. Letters denoting design may establish interchangeability of all parts, as in the M-design core barrel, or only of certain parts, as in the X-design core barrel. CF: group; range.

designated size

The particle size at which it is desired to separate a feed by a sizing operation.

designed borehole deflection

The turning of a borehole along a different course at depth. This may be achieved, but not without difficulty. The cutting bit is guided upon its new course by the curved surface of a deflecting wedge that is positioned with the aid of a modified Oehman instrument. In petroleum drilling, much use is made of holes that are deflected at a predetermined depth. The technique is known as whipstocking.

design horsepower

The specified horsepower multiplied by a service factor. It is the value used to select the chain size for a chain drive.


The removal of silica from a rock or magma by the breakdown of silicates and the resultant freeing of silica, or by reaction between a body of magma and the surrounding wall rock.


A practice of jetting oxygen into pig iron before it is charged into the steel furnace; this oxidizes and removes most of the silicon.


The process of removing silver (and gold) from lead after softening. See also: Parkes process; Pattinson process.


The removal of slimes from coal or a mixture of coal and water, however accomplished.

desliming screen

A screen used for the removal of slimes from larger particles, usually with the aid of water sprays.


Fines removal by wet methods.


A former name for stilbite.


The amorphous groundmass, which is transparent in thin sections, binding together the constituents of bituminous coal of high grade. Applies to the transparent variety of residuum found in high-grade coals.


A banded adinole.


The reverse process of adsorption whereby adsorbed matter is removed from the adsorbent. The term is also used as the reverse process of absorption.


See: diabandite.

destressed area

a. In strata control, a term used to describe an area where the force is much less than would be expected after considering the depth and type of strata. CF: overstressed area. Syn: zone of substantial deformation.

b. A region of low stress behind the walls of a stoped-out region.


In deep mining, relief of pressure concentrations induced by mining or caused by geological factors. Performed by drilling and blasting to loosen the zones of peak stress. The peak load surrounding the excavation walls is thus transferred deeper into the undisturbed rock, and a protective barrier is formed.

destructive distillation

The distillation of solid substances accompanied by their decomposition. The destructive distillation of coal results in the production of coke, tar products, ammonia, gas, etc.

destructive testing

Testing methods, the use of which destroy or impair the part or product insofar as its intended use is concerned, but which give proof or an indication of the strength or quality of similar or duplicate parts or products. Such tests involve the subjection of the test piece to various influences, of destructive magnitude, such as impact, stress, pressure, cyclic movement, etc. See also: nondestructive testing.

desulfurization of steel

The removal of a high proportion of sulfur from steel by injection of calcium or magnesium.


To free from sulfur; to remove the sulfur from an ore or mineral by some suitable process, as by roasting.

detachable bit

A drilling bit that is threaded or tapered and is removable from the drill steel; not formed as an integral part of the drill steel. The all-steel bit can be resharpened, but the tungsten carbide insert type may be nonresharpenable. Also known as rip bit or knockoff bit. See also: bit; hot miller.

detached head pulley

See: head pulley.

detaching hook

An appliance that releases automatically the winding rope from the cage should an overwind occur. See also: wedge guide.


See: decollement.

detail drawing

A large-scale drawing showing all small parts, details, dimensions, etc.

detailed soil survey

The final soil tests at site as guided by the general soil survey. The tests may be performed in situ by mobile laboratory units, or the samples are sent to the nearest soils laboratory. See also: general soil survey; preliminary soil survey.

detaline system

A nonelectric system of initiating blasting caps in which the energy is transmitted through the circuit by means of a low-energy detonating cord.


a. See: magnetic detector.

b. See: seismometer. c. The component of a remote-sensing system that converts electromagnetic radiation into a signal that can be recorded. See also: pickup. Syn: radiation detector. d. See: sensor.

determinative gemology

The science of differentiating (1) between the various gemstones, (2) between gemstones and their substitutes, and (3) among such substitutes. See also: gemology.

determinative mineralogy

That branch of mineralogy that comprises the measurement of the nature, composition, and classification of minerals by means of physical tests (e.g., density, hardness), chemical analyses both qualitative and quantitative, spectrochemical analyses including both absorption and emission spectra, electron probe microanalyses, autoradiography, thermal analyses, optical tests in both transmitted and reflected light, electron microscopy, diffraction of X-rays or electrons, and crystallographic analyses.


Treatment by chlorination of tinbearing scrap for recovery of tin as its chloride.


To cause to explode by the application of sudden force.

detonating cord

A flexible cord made of wound hemp or jute threads covered with plastic containing a center core of high explosive (PETN) and used to initiate other explosives.

detonating fuse

A fuse consisting of high explosive that fires the charge without the assistance of any other detonator. It consists of a high-explosive core of pentaerythritol tetranitrate (PETN) enclosed in tape and wrapped with textile countering yarns. Usually, this fuse is then reinforced or completely enclosed in a strong waterproof plastic outer cover. The finished external diameter is normally about 0.2 in (5 mm). Primacord is the best known brand. See also: Cordtex; safety fuse.

detonating gas

A gaseous mixture that explodes violently on ignition (as two volumes of hydrogen with one volume of oxygen, forming water).

detonating powder

Any powder or solid substance that when heated or struck explodes with violence and a loud report.

detonating primer

A name applied for transportation purposes to a device consisting of a detonator and an additional charge of explosives, assembled as a unit.

detonating rate

The velocity with which the explosion wave travels through the column of charge.

detonating relays

A device for obtaining short-delay blasting in conjunction with the detonating fuse. It consists essentially of two open-ended delay detonators coupled together with flexible neoprene tubing.

detonating tube

A eudiometer for making explosions.


a. An explosive decomposition or explosive combustion reaction that moves through the reactant(s) at greater than the speed of sound in the reactant(s) to produce (1) shock waves and (2) significant overpressure, regardless of confinement.

b. An extremely rapid explosion; the firing of an explosive charge by fuse or electric detonator. c. The action of converting the chemicals in an explosive charge to gases at a high pressure, by means of a self-propagating shock wave passing through the charge.

detonation pressure

The pressure produced in the reaction zone of a detonating explosive and is a function of explosive density and detonation velocity.

detonation traps

Devices that prevent a detonation initiated in one part of a system from propagating to another.

detonation velocity

a. The velocity at which a detonation progresses through an explosive.

b. See: velocity of detonation.


A device for producing detonation in a high-explosive charge, and initiated by a safety fuse or by electricity. Syn: percussion cap. See also: blasting cap; electric detonator.

detonator case

A container for carrying detonators in mines. It is so constructed that, when closed, a detonator or the leads of a detonator cannot come into contact with either the metal of the case or any metal outside the case.


Pertaining to or formed from detritus; said esp. of rocks, minerals, and sediments. See also: clastic.

detrital deposits

Placer or detrital deposits are composed of minerals that have been released by weathering and later have been transported, sorted, and collected by natural agencies into valuable deposits. Such minerals are usually of high specific gravity and are resistant to abrasion and weathering. Examples are gold, diamonds, platinum, tin (cassiterite), monazite, magnetite, and ilmenite, these last two being the common constituents of black sand.

detrital fan

See: alluvial fan.

detrital mineral

Any mineral grain resulting from mechanical disintegration of parent rock; esp. a heavy mineral found in a sediment or weathered and transported from a vein or lode and found in a placer or alluvial deposit.

detrital rock

A rock composed primarily of particles or fragments detached from preexisting rocks either by erosion or by weathering; specif. a sedimentary rock having more than 50% detrital material. CF: chemical rock.


A collective term for loose rock and mineral material that is worn off or removed by mechanical means, as by disintegration or abrasion; esp. fragmental material, such as sand, silt, and clay, derived from older rocks and moved from its place of origin. CF: debris.


Referring to reactions between primary magmatic minerals and the water-rich solutions that separate from the same body of magma at a late stage in its cooling history. Syn: epimagmatic. See also: autometamorphism.


A general term applied to crystals whose shapes have been acquired or modified by mechanical or chemical processes acting on the original forms.

De-Vecchis process

A method for the smelting of pyrites that entails the roasting and magnetic concentration of the raw material followed by reduction in a rotary kiln or electric furnace. The product may be briquetted and reduced in the blast furnace, but is better smelted in an electric furnace.


a. To open a mine and ore; more or less, to search, prospect, explore.

b. To traverse a mineralized body horizontally by drives and vertically by shafts or winzes to prove its extent. c. To open up orebodies by shaft sinking, tunneling, or drifting.

developed ore

See: developed reserve.

developed reserve

Ore that has been exposed on three sides and for which tonnage and quality estimates have been made; ore essentially ready for mining. CF: proved reserve. Syn: developed ore; ore in sight; blocked-out ore; assured mineral.


a. The preparation of a mining property or area so that an orebody can be analyzed and its tonnage and quality estimated. Development is an intermediate stage between exploration and mining.

b. To open up a coal seam or orebody as by sinking shafts and driving drifts, as well as installing the requisite equipment. c. Work of driving openings to and in a proved orebody to prepare it for mining and transporting the ore. d. The amount of ore in a mine developed or exposed on at least three sides. e. S. Afr. The work done in a mine to open up the paying ground or roof and, in particular, to form drives or haulages around blocks of ore, which are then included under developed ore reserves. f. A geologic term, applied to those progressive changes in fossil genera and species that have followed one another during the deposition of the strata of the Earth. g. In construction of a water well, the removal of fine-grained material adjacent to a drill hole, enabling water to enter the hole more freely. h. Exploitation of ground water.

development drift

a. A main tunnel driven from the surface, or from a point underground, to gain access to coal or ore for exploitation purposes.

b. Slant.

development drilling

Delineation of the size, mineral content, and disposition of an orebody by drilling boreholes.

development drivages

The shafts, tunnels, laterals, crosscuts, and staple pits to prove and render accessible the coal or ore to be extracted. See also: productive development; unproductive development.

development engineer

In bituminous coal mining, one who operates a hoist to raise and lower workers, rock, and supplies during development work (sinking shafts and driving horizontal underground passages prior to the actual mining of coal from a seam).

development miner

See: miner.

development plan

A plan showing the proposed development of the mine workings, and kept for operational purposes.

development rock

S. Afr. The rock broken during development work in payable ground, which contains both valuable and barren rock and is, therefore, included in the tonnage sent to the reduction plant of a mine.

development sampling

Sampling for the establishment of reserves and conducted primarily upon the exposures along the development drivages. See also: reserve.

development work

Work undertaken to open up orebodies as distinguished from the work of actual ore extraction. Sometimes development work is distinguished from exploratory work on the one hand and from stope preparation on the other.

Devereaux agitator

used in leach agitation of minerals.


To change the course of a borehole. CF: walk; wander.


Syn. for deflecting.


a. The departure of a drilled hole from being straight. The hole may be either vertical or inclined, and the departure may be in any direction. Deviation may be intentional, as in directional drilling, or undesirable. Syn: deflection.

b. In more general use, the angle of departure of a well bore from the vertical, without reference to direction. c. The distance, measured in a horizontal plane, between two surveyed points in a borehole or between the collar and any point below the collar in a borehole. Also called dislocation; throw.


A monoclinic mineral, CaCu (sub 4) (SO (sub 4) ) (sub 2) (OH) (sub 6) .3H (sub 2) O ; emerald-green to verdigris-green. Formerly called devillite; herrengrundite; lyellite; urvolgyite.


See: devilline.

devil's dice

Cubes of fully or partially oxidized and hydrated pseudomorphs of pyrite in alluvial workings.

devil's dough

A hard, gray-white siliceous rock.


a. Deferred crystallization, which, in glassy igneous rocks, converts obsidians and pitchstones into dull cryptocrystalline rocks (commonly called felsites) consisting of minute grains of quartz and feldspar. Such devitrified glasses reveal their originally vitreous nature by traces of perlitic and spherulitic textures.

b. The process by which glassy rocks break down into definite minerals, which are commonly minute, chiefly quartz and feldspar. c. Any change from a glassy state to a crystalline state after solidification. d. In ceramics, a surface defect manifested by loss of gloss as a result of crystallization.


To destroy the glasslike character of volcanic glasses by changing from the vitreous state to the crystalline state.


Progressive loss of volatiles by the substance undergoing coalification process.


The fourth period, in order of decreasing age, of the periods making up the Paleozoic era. It followed the Silurian period and was succeeded by the Mississippian period. Also, the system of strata deposited at that time. Sometimes called the Age of Fishes.

De Vooy's process

The sink-float or dense-media process used for coal cleaning. The separating fluid is a clay-barite water pulp.


To remove water from a mine; an expression used in the industry in place of the more technically correct word, unwater.


a. The removal of water from a drowned shaft or waterlogged workings by pumping or drainage as a safety measure or as a preliminary step to resumption of development in the area. CF: unwatering.

b. The draining of an aquifer when adjacent wells or mine workings are pumped. c. The mechanical separation of a mixture of coal and water into two parts, one which is relatively coal-free, the other relatively water-free, with respect to the original mixture. d. The mechanical separation of solid matter from water in which it is dispersed, by such equipment as thickeners, classifiers, hydrocyclones, filters, and centrifuges. Coarser coal sizes may be dewatered by slotted screens or perforated bucket elevators. e. The process in which solid material, either submerged or containing liquid, is conveyed or elevated in a manner that allows the liquid to drain off while the solid material is in transit.

dewatering classifier

A settling tank for clarifying washer circulating water or for concentrating gold slimes before cyaniding. The tank may have a continuously working rake that moves the sludge toward the outlet pipe in the bottom. See also: dryer.

dewatering elevator

Similar to the continuous bucket elevator, it is often used in sand and gravel plants where the dredge line discharges to a sump. The dewatering elevator digs the material from the sump, allowing the water to drain out through perforations in the backs of the buckets while being elevated, and discharges to the plant for further processing.

dewatering screen

A screen used for the separation of water from solids.


A mixture of a disordered clinochrysotile or lizardite with a talclike mineral.


An orthorhombic mineral, Pb (sub 3) (UO (sub 2) ) (sub 6) H (sub 2) (PO (sub 4) ) (sub 4) O (sub 4) .12H (sub 2) O ; strongly radioactive; canary yellow; associated with torbernite and other secondary uranium minerals.


The temperature to which air must be cooled, at constant pressure and constant water vapor content, in order for saturation to occur. Since the pressure of the water vapor content of the air becomes the saturation pressure, the dewpoint may also be defined as the temperature at which the saturation pressure is the same as the existing vapor pressure. Also called saturation point.

dewpoint hygrometer

An instrument for determining the dewpoint; a type of hygrometer.

dextral fault

See: right-lateral fault.


A carbohydrate, C (sub 6) H (sub 18) O (sub 5) , hydrolyzed from starch by dilute acids. Used in flotation as depressant.

d'Huart reagent

An etching reagent that reveals not only the macrostructure and faults, such as piping, segregation, particularly sulfur and phosphorus, and cracks, but also slip lines in mild steel that has been stressed beyond its elastic limit. Composition is 100 mL of distilled water, 100 mL of concentrated hydrochloric acid, and 40 g of crystallized chromic acid, 16 g of anhydrous nickel chloride.


A ferroan variety of clinchlore. Syn: destinezite.


In the United States, an intrusive rock whose main components are labradorite and pyroxene and that is characterized by ophitic texture. As originally applied by Brongniart in 1807, the term corresponded to what is now recognized as diorite. The word has come to mean a pre-Tertiary basalt in Germany, a decomposed basalt in England, and a dike-rock with ophitic texture in the United States and Canada (Johannsen, 1939). CF: trap. Syn: dolerite.


Composed of or resembling diabase.


Pertaining to a texture in metamorphic rock that consists of intricately intergrown and interpenetrating constituents, usually with rodlike shapes.


The transgression, across time planes or biozones, by a rock unit whose age differs from place to place; the state or condition of being diachronous.


Said of a rock unit that is of varying age in different areas or that cuts across time planes or biozones; e.g., said of a sedimentary formation related to a narrow depositional environment, such as a marine sand that was formed during an advance or recession of a shoreline and becomes younger in the direction in which the sea was moving. Syn: time-transgressive. CF: synchronous.


An axial rotation of 180 degrees . Syn: twofold. CF: axis of symmetry.


A hydrated ferric phosphate and sulfate mineral, brown or yellowish in color.


Any change occurring within a sediment after its deposition and during and after its lithification, exclusive of weathering. It includes such processes as compaction, cementation, replacement, and crystallization, under normal surficial conditions of pressure and temperature.

diagenetic deposits

Deposits consisting dominantly of minerals crystallized out of sea water, such as manganese nodules.

diagnostic mineral

a. A mineral, such as olivine or quartz, whose presence in an igneous rock indicates whether the rock is undersaturated or oversaturated. There are also diagnostic minerals in sedimentary and metamorphic rocks. Syn: symptomatic mineral.

b. A mineral whose presence permits certain deductions pertaining to a geologic history of a rock or sediment.

diagonal fault

See: oblique fault.

diagonal joints

a. Joints diagonal to the strike of the cleavage.

b. In igneous rocks, joints that occur at 45 degrees to the flow lines and are caused by shear.

diagonal-slip fault

See: oblique-slip fault.


a. A compass used for surface and underground surveying. It is fitted with sights, spirit levels, and a vernier, and mounted on a tripod. Syn: mining dial.

b. Corn. To make a mine survey.


a. The process of running an underground traverse with a mining dial. Also spelled: dialling.

b. Surveying, usually magnetic, using miner's dial.


A dark green or bronze-colored monoclinic pyroxene, which in addition to the prismatic cleavages has others parallel to the vertical pinacoids. Mohs hardness, 4; sp gr, 3.2 to 3.35. Used also as a prefix to many rocks containing the mineral. See also: pyroxene.


A former name for rhodochrosite.


A method of separating compounds in solution or suspension by their differing rates of diffusion through a semipermeable membrane, some colloidal particles not moving through at all, some moving slowly, and others diffusing quite readily. CF: osmosis. See also: electrodialysis.


Having a small, negative magnetic susceptibility. All materials that do not show paramagnetism or magnetic order are diamagnetic. Typical diamagnetic minerals are quartz and feldspar. CF: paramagnetic.


The property of certain substances by virtue of which they are repelled from both poles of a magnet and tend to set with the longer axis across the lines of magnetic force. CF: ferrimagnetism; paramagnetism.


See: diamondiferous.

diametric rectifier circuit

A circuit that employs two or more rectifying elements with a conducting period of 180 electrical degrees, plus the commutating angle.


a. An isometric mineral, a form of carbon, C ; crystallizes in octahedra, dodecahedra, or cubes, commonly with curved edges and striated faces; rarely twinned; has octahedral cleavage and conchoidal fracture. Fresh cleavages have adamantine luster, but crystal faces are commonly greasy; colorless when pure but pale tints to black (bort) with impurities. The hardest natural substance, it defines 10 on the Mohs hardness scale and 15 on the Povarennykh scale, but ranges from 42 to 46 on a linearized Mohs scale. Its high refractive index (n = 2.42) and strong dispersion give fire to faceted gems. Diamond occurs in kimberlite pipes and dikes, also in river and beach placers. See also: congos.

b. A crystalline material resembling diamond such as rock crystal (quartz) locally known as "Bristol diamond," "Herkimer diamond," "Lemont diamond," "Lake George diamond," or "Arkansas diamond." See also: industrial diamonds; manmade diamond. c. A pointed wooden or iron arrangement placed between rails, just before a curve or switch, where tram cars are liable to be derailed, to force them to remain on the rails.

diamond ballas

An important industrial variety of diamond. The stones are spherical masses of minute diamond crystals arranged more or less radially. They have no well-defined cleavage planes and thus have great resistance to abrasion. While the term, ballas, was first applied to such stones from Brazil, diamonds of similar structure known as Cape and African ballas are found. In color, ballas ranges from white to varying shades of black. While Cape and African ballas are not as hard as the Brazilian, they include some fine and unusual stones. Production is small. Rarely, if ever, used for diamond drilling but very valuable for diamond tools.

diamond bit

A rotary drilling bit studded with bort-type diamonds. Also called boart bit; boart-set bit. Syn: bort bit; bort-set bit.

diamond boring

Precision boring with a shaped diamond (but not with other tool materials).

diamond chip

A thin, tabular chip of an uncut diamond crystal, weighing less than 0.75 carat.

diamond chisel

A cutting chisel having a diamond or V-shaped point.

diamond cleavage

The plane along which a diamond crystal can be split easily. The four planes paralleling the faces of an octahedron are those generally referred to as the cleavage planes, or diamond cleavage. All crystalline diamonds are more or less brittle and will be fractured by a sufficiently violent blow, but the irregular surface of a fracture cannot be mistaken for the brilliant flat surface produced by cleaving. The carbon has no cleavage, and in ballas cleavage is absent or very poorly defined.

diamond cleaving

The act or process of splitting diamonds into smaller pieces, which may be more readily used as tool points, gems, or drill diamonds.

diamond concentration

The ratio of the area of a single-layer bit face covered by the inset diamonds or, in an impregnated bit, the bulk proportion of the crown occupied by diamonds.

diamond content

The number of carats of diamonds inset in the crown of a diamond bit. Also called stone content; stone weight.

diamond core drill

A rotary-type drill machine using equipment and tools designed to recover rock samples in the form of cylindrical cores from rocks penetrated by boreholes. See also: core drill; diamond drill.

diamond coring

The act or process of obtaining a core sample of rock material using a diamond-inset annular bit as the cutting tool. This tubular bit and attached core barrel are rotated at a speed under controlled pressure by means of hollow steel, flush-jointed rods through which water is pumped to cool the bit and remove rock cuttings. With the advance of the bit, a cylindrical core of rock passes up into the core barrel, where it is held by a core lifter or other device.

diamond count

a. The number of diamonds set in the crown of a specific diamond bit. Also called bit count; stone count.

b. Sometimes incorrectly used to indicate the average size of the diamonds inset in a specific bit. See also: carat count.

diamond crown

The cutting bit in diamond drilling. It consists of a steel shell containing small cavities in its face and edges into which black diamonds are set. In some types of crown the diamonds can be removed and reset for further use. Grooves, called waterways, are usually provided in the face of the crown to allow the passage of the drilling fluid. For surface-set bits in diamond drilling, it is recommended that 2 to 20 stones per carat should be used in soft ground (such as shale); 10 to 80 stones per carat in medium ground (such as sandstone); and 20 to 150 stones per carat in hard ground (such as granite). See also: burned bit.

diamond cubic

With respect to atomic arrangements, similar to the diamond in having the two face-centered cubic arrangements of atom centers either of which is displaced with respect to the other by one-fourth of the diagonal of the unit cube.

diamond cutter

a. An individual skilled in the art of shaping diamonds as gems.

b. A tool in which a single diamond, shaped as a cutting point, is inset.

diamond cutting

One of the three processes by which diamonds are prepared for use as ornaments or in the arts, the others being diamond cleaving and diamond polishing.

diamond drill

a. A drilling machine with a rotating, hollow, diamond-studded bit that cuts a circular channel around a core, which can be recovered to provide a more or less continuous and complete columnar sample of the rock penetrated.

b. Diamond drilling, a common method of prospecting for mineral deposits. Also called adamantine drill; diamond core drill; rotary drill. See also: core drill; hydraulic circulating system.

diamond-driller helper

One who assists in the erection and operation of a core drill that bores into rock, earth, and other minerals to obtain core samples. Also called core-driller helper; core-drill-operator helper; diamond-point-drill-operator helper; drill-runner helper; shot-core-drill-operator helper; test-borer helper; test-hole-driller helper; wash-driller helper.

diamond drilling

The act or process of drilling boreholes using bits inset with diamonds as the rock-cutting tool. The bits are rotated by various types and sizes of mechanisms motivated by steam, internal-combustion, hydraulic, compressed-air, or electric engines or motors. A common method of prospecting for mineral deposits. See also: diamond drill.

diamond-drill sample

The core brought to the surface in the core barrel. The cuttings in the uprising drilling fluid will also provide sampling material. Syn: core recovery.

diamond dust

a. Finely fragmented or powdered diamonds used as a cutting, grinding, and polishing abrasive or medium.

b. A diamond powder produced in the cutting of gems.

diamond exposure

The proportional mass of a diamond protruding beyond the surface of a matrix metal in which the diamond is inset. CF: bit clearance. Syn: stone exposure.

diamond grade

The worth of a diamond as based on an individual sorter's interpretation of somewhat arbitrary standards of color, presence of flaws, soundness, and shape.


Any substance containing diamonds, generally applied to rock or alluvial material containing diamonds, but may also refer to diamond-impregnated substances, such as the crown of a diamond-impregnated drill bit.

diamond impregnated

Having diamonds distributed throughout a matrix.

diamond life

The amount of cutting a diamond will accomplish before being completely worn away by abrasion. In bits, diamond life usually is expressed in the number of feet drilled in a specific rock before the inset diamonds become too dulled to continue cutting or are lost by rollout or completely worn away by abrasion.

diamond matrix

a. A metal or metal alloy forming the material in which the diamonds inset in a bit crown are embedded. Also called bit-crown metal; bit-crown matrix; bit matrix; crown metal; matrix.

b. The rock material in which diamonds are formed naturally and occur, such as in kimberlite.

diamond needle

A small-diameter hollow metal tube attached to a flexible rubber tube through which air is pulled by a suction or vacuum pump. The suction created at the tip of the metal tube enables a bit setter to pick up and place a small diamond in a bit mold with greater facility than with tweezers. Called a needle because the metal tube generally is made by using a discarded hypodermic needle. Also called diamond pickup needle; diamond pickup tube; diamond pipe.

diamond pipe

a. Term used for an occurrence of kimberlite in volcanic pipes large enough and sufficiently diamondiferous to be minable. The size and shape of these pipes depend on the position of the planes of structural weakness in the country rock through which the molten kimberlite passed. They may be columnar, tabular, or irregular in shape, and where mining is deep enough the diamond pipe is found to decrease in area and assume a dikelike habit.

b. See: diamond needle.

diamond powder

See: diamond dust.

diamond pressure

The proportional amount of the total feed pressure applied to a diamond bit theoretically borne by an individual diamond inset in the face of the bit. Also called pressure per diamond; pressure per stone; stone pressure.

diamond-pyramid hardness test

An indention hardness test employing a 136 degrees diamond-pyramid indenter and variable loads enabling the use of one hardness scale for all ranges of hardness from very soft lead to tungsten carbide. See also: Vickers hardness test.

diamond saw

A circular metal disk having diamonds or diamond dust inset in its cutting or peripheral edge. Employed to cut rocks and other brittle substances. See also: diamond wheel.

diamond-saw splitter

See: core saw.

diamond scale

Instrument on which diamonds are weighed with weight units calibrated in carats; scales vary from a folding 50-carat-capacity type, small enough to fit in a coat pocket when closed, to those large enough to weigh several thousand carats at one time.

diamond scrap

As used in the diamond-drilling industry; broken diamonds and diamond fragments deemed unfit for reuse in a diamond bit. In other industries using diamond-pointed tools, any piece of diamond salvaged from a tool and deemed unfit for reuse in the same kind of tool.

diamond screen

A perforated metal or wirecloth sieve used to sort diamonds or fragments of diamonds according to size.

diamond-set bit

A rock-boring or rock-cutting tool, the cutting points of which are inset diamonds.

diamond-set inserts

Small, shaped metallic slugs inset with diamonds designed to be brazed or welded into slots or depressions machined in a metal bit or reaming-shell blank.

diamond-set ring

A powdered metal-alloy band encircling a reaming shell in which diamonds are inset mechanically.

diamond spar

Syn: corundum.

diamonds per carat

The number of relatively equal size diamonds having a total weight of 1 carat. Also called stone per carat.

diamond tin

Large bright crystals of cassiterite.

diamond-tooth saw

A circular saw for cutting stone with points of the teeth made of pieces of diamonds.

diamond washer

An apparatus used for washing diamondiferous gravel.

diamond wheel

a. A grinding wheel in which crushed and sized industrial diamonds are held in a resinoid, metal, or vitrified bond.

b. See: diamond saw.


See: columbite.


a. The quality or state of being diaphanous. Specif., the ability of a mineral to transmit light. CF: transparent; semitransparent; translucent; opaque.

b. Degrees of transparency of minerals. CF: transparent; translucent; opaque. c. See: transparency.


Allowing light to show or to shine through.


a. See: allagite.

b. A monoclinic mineral, Pb (sub 2) Ag (sub 3) Sb (sub 3) S (sub 8) .


A porous or permeable membrane separating anode and cathode compartments of an electrolytic cell from each other or from an intermediate compartment.

diaphragm jig

In the gravity concentration of minerals, a jig with a flexible diaphragm used to pulse water. The Bendelari, Pan-American, Denver, and Conset are examples.

diaphragm pump

A positive displacement pump used for lifting small quantities of water and discharging them under low heads. It has a plunger arm operating either on an eccentric shaft or a rocker arm thrusting on a rubber diaphragm stretched over a cylinder. As the diaphragm is depressed, the water and air in the cylinder are forced out through the discharge side of the pump. As the diaphragm is lifted, a vacuum is created in the cylinder, and water is forced in.

diaphragm-type washbox

A washbox in which the pulsating motion is produced by the reciprocating movement of a diaphragm.


See: retrograde metamorphism.


A crystalline rock in which minerals characteristic of a lower metamorphic grade have developed by retrograde metamorphism at the expense of minerals peculiar to a higher metamorphic grade.


A dome or anticlinal fold in which the overlying rocks have been ruptured by the squeezing-out of plastic core material. Diapirs in sedimentary strata usually contain cores of salt or shale; igneous intrusions may also show diapiric structure.

diapir fold

An anticline in which a mobile core, such as salt, has ruptured the more brittle overlying rock. Syn: piercement dome; piercement fold.


Said of the rock of a minor intrusion that consists of a differentiate, i.e., its composition is not the same as that of the parent magma. CF: aschisite; aschistic.


An orthorhombic mineral, AlO(OH) ; white, colorless, or pale tints; in bauxite and emery deposits; a source of aluminum. Formerly spelled disaporite. Syn: kayserite.

diaspore clay

A high-alumina refractory clay consisting essentially of the mineral diaspore. It has been interpreted as a desilication product of associated flint clay and other kaolinitic materials. Commercial diaspore of first-grade quality contains more than 68% alumina. See also: burley clay.


A colloidal form of aluminum hydroxide in bauxite. Syn: sporogelite; cliachite.


A relatively short interruption in sedimentation, involving only a brief interval of time, with little or no erosion before deposition is resumed; a paraconformity of very small time value.


Asterism seen by transmitted light. See also: asterism; epiasterism.


The processes of deformation in the Earth's crust that produce its continents and ocean basins, plateaus and mountains, and major folds and faults. Syn: tectonism.


a. Transmitting infrared radiation.

b. Allowing the free passage of the rays of heat as a transparent body allows free passage of light.


A microscopic unicellular plant with an envelope (frustule) or outer skeleton of hydrated silica, close to opal in composition, and usually in two parts. Diatoms inhabit both fresh water and salt water, and in places their frustules form masses of diatomaceous earth or shale hundreds of feet thick.


Composed of or containing diatoms or their siliceous remains.

diatomaceous earth

See: diatomite.


A light-colored soft friable siliceous sedimentary rock, consisting chiefly of opaline frustules of the diatom, a unicellular aquatic plant related to the algae. Some deposits are of lake origin, but the largest are marine. Owing to its high surface area, high absorptive capacity, and relative chemical stability, diatomite has a number of uses, esp. as a filter aid and as an extender in paint, rubber, and plastics. The term is generally reserved for deposits of actual or potential commercial value. Syn: diatomaceous earth; kieselguhr; guhr; tripoli. Obsolete syn: infusorial earth; tripoli-powder. See also: tripolite. CF: diatomite.

diatom ooze

A deep-sea deposit, resembling flour when dry, largely composed of the frustules of diatoms and containing a small but variable proportion of calcareous organisms and mineral particles.


Having a single distinct diagonal cleavage; applied to certain crystals.

diatom saprokol

A saprokol containing a large amount of diatoms.


A breccia-filled volcanic pipe that was formed by a gaseous explosion.

dibutyl carbinol

2-methyl-l-butanol; a frother used in the flotation process.

dice mineral

A Wisconsin term for small cubic galena.

dicey clay

Any clay or mudstone with a cuboidal fracture, as in the Kimmeridge clay.

dichroic colors

A term loosely used to refer to either the two colors observable in a dichroic stone or the three colors in a trichroic stone. Syn: twin colors. See also: dichroscope.


a. Pleochroism of a crystal, which is indicated by two different colors or two shades of the same color. In plane-polarized light, dichroic minerals change color upon rotation. CF: trichroism; pleochroism.

b. Color change owing to change in the spectrum of illumination; e.g., alexandrite, which is green in sunlight but red by tungsten incandescent light. See also: chrysoberyl. c. The property of some surfaces to reflect light of one color while transmitting light of another.


A former name for iron-rich cordierite that may have been the navigation stone of the Vikings; reveals maximum light polarization in the southern sky.


A salt containing the divalent (Cr (sub 2) O (sub 7) ) (super 2-) radical.


a. An instrument designed to detect two of the different colors emerging from pleochroic (that is, dichroic or trichroic) minerals. Contains a rhomb of Iceland spar and a lense system in a short tube, and exhibits the two colors side by side. See also: dichroic colors.

b. An instrument to detect two colors transmitted by pleochroic minerals and display them side-by-side.


A monoclinic mineral, (K,Ba)(Na,Ca) (sub 5) (Mn,Fe,Mg) (sub 14) Al(PO (sub 4) ) (sub 12) (OH,F) (sub 2) ; forms a series with arrojadite.


A green, hydrous phosphate mineral, chiefly of manganese, iron, and sodium.


A monoclinic mineral, Al (sub 2) Si (sub 2) O (sub 5) (OH) (sub 4) ; kaolinite-serpentine group; polymorphous with halloysite, kaolinite, and nacrite, each having a different stacking order of identical layers (polytypy); commonly in hydrothermal veins.


A crystal having two of the three axes inclined to the third and perpendicular to each other.


a. The name applied to commercial mixtures of rare-earth elements obtained from monazite sand by extraction followed by the elimination of cerium and thorium from the mixture. The name is used like that of an element in naming mixed oxides and salts. The approximate composition of didymium from monazite, expressed as rare-earth oxides, is 46% lanthana, La (sub 2) O (sub 3) ; 10% praseodymia, Pr (sub 6) O (sub 11) ; 32% neodymia, Nd (sub 2) O (sub 3) ; 5% samaria, Sm (sub 2) O (sub 3) ; 0.4% yttrium earth oxides; 1% ceria, CeO (sub 2) ; 3% gadolinia, Gd (sub 2) O (sub 3) ; and 2% others. The mineral bastnaesite could also be a source of didymium mixtures.

b. The name didymium has also been applied to mixtures of the elements praseodymium and neodymium because such mixtures were once thought to be an element; it was assigned the symbol, Di.


A former name for a plagioclase mineral.


a. See: bell tap.

b. A piece of hard iron, placed in a mortar to receive the blow of a stamp or in a pan to receive the friction of a muller as ore is crushed between the die and the stamp or muller.

die-casting alloys

Alloys that are suitable for die casting and that can be relied on for accuracy and resistance to corrosion when cast. Aluminum-, copper-, tin-, zinc-, and lead-base alloys are those generally used.

die collar

See: bell tap.


a. A material that offers relatively high resistance to the passage of an electric current but through which magnetic or electrostatic lines of force may pass. Most insulating materials, for example, air, porcelain, mica, and glass, are dielectrics; and a perfect vacuum would constitute a perfect dielectric.

b. An insulator. A term applied to the insulating material between the plates of a capacitor.

dielectric constant

The numerical expressions of the resistance to the passage of an electric current between two charged poles. It is the ratio of the attraction of two oppositely charged poles as measured in a vacuum to their attraction in a substance. The dielectric constant, which corresponds to permeability in magnetic materials, is a measure of the polarizability of a material in an electric field. This property determines the effective capacitance of a rock material and consequently its static response to any applied electric field, either direct or alternating. The dielectric constant of a vacuum is unity.

dielectric heating

A method of high-frequency heating in which the object to be heated, which must be nonconducting, is placed in a high-frequency alternating field where it is heated by the continually reversed polarization of the molecules. Applied in the foundry for drying sand cores.

dielectric separation

Method of ore treatment based on differences between dielectric constants of minerals suspended in an intermediate nonconducting fluid, when subjected to electric fields. Of limited use in laboratory work.

dielectric strength

The maximum potential gradient that a dielectric material can withstand without rupture.


An isometric mineral, Ni (sub 3) As ; in gray-white cubes at Radstadt, Salzburg, Austria.

die nipple

See: bell tap.

diesel hammer

A pile driving drophammer operated by a type of diesel engine.


In a compressor, explosions of mixtures of air and lubricating oil in the compression chambers or other parts of the air system.

diesel particulate matter

a. Exhaust material, excluding water, that results from the incomplete combustion of fuel and lubricating oil in a diesel engine. The particulates collected on a filter after dilution of the exhaust with ambient air, are carbonaceous solid chain aggregates with adsorbed or condensed organic compounds.

b. The fumes (solid condensation particles) and adsorbed gases that are emitted from a diesel engine as a result of the combustion of diesel fuel. Abbrev. DPM. DPM is a complex mixture of chemical compounds, composed of nonvolatile carbon, hundreds of thousands of different adsorbed or condensed hydrocarbons, sulfates, and trace quantities of metallic compounds. DPM is of special concern because it is almost entirely respirable, with 90% of the particles, by mass, having an equivalent aerodynamic diameter of less than 1.0 mu m. This means that the particles can penetrate to the deepest regions of the lungs and, if retained, cause or contribute to the development of lung disease. Of equal concern is the ability of DPM to adsorb other chemical substances, such as (1) potentially mutagenic or carcinogenic polynuclear aromatic hydrocarbons (PAHs); (2) gases, such as sulfur dioxide and nitrogen dioxide; and (3) sulfuric and nitric acids. DPM carries these substances into the lungs, where they may be removed and transported by body fluids to other organs, where they may cause damage.

diesel rig

Any drill machine powered by a diesel engine.

diesel truck

In opencast mining, a powerful and robust diesel-engined vehicle carrying from a few to more than 100 cubic yards of earth or rock. Also used in trackless transport in tristate mines.

die steels

Steels of plain-carbon or alloy types; they must be of high quality, which is usually attained by special methods of processing. Essentially, they are steels used in making tools for cutting, machining, shearing, stamping, punching, and chipping.

Dietert tester

An apparatus for the direct reading of a Brinell hardness after impression without the aid of magnification or conversion tables.


A monoclinic mineral, Ca (sub 2) (IO (sub 3) ) (sub 2) (CrO (sub 4) ) ; dark golden-yellow; forms prismatic, tabular, fibrous, or columnar crystals; at Atacama, Peru.

difference in gage of drill bits

The difference in diameter of the bits when passing from one length (change) of drill steel to the next longer one of a set.

difference of potential

The difference in electrical pressure existing between any two points in an electrical system or between any point of such a system and the Earth. Determined by a voltmeter.

differential compaction

The uneven settling of homogeneous earth material under the influence of gravity (as where thick sediments in depressions settle more rapidly than thinner sediments on hilltops) or by differing degrees of compactability of sediments (as where clay loses more interstitial water and comes to occupy less volume than sand).

differential curvature

A quantity represented by the acceleration due to gravity times the difference in the curvatures in the two principal planes; i.e., g(1/p (sub 1) - 1/p (sub 2) ) where p (sub 1) and p (sub 2) are the radii of curvature of the two principal planes.

differential erosion

Erosion that occurs at irregular or varying rates, caused by the differences in the resistance and hardness of surface materials; softer and weaker rocks are rapidly worn away, whereas harder and more resistant rocks remain to form ridges, hills, or mountains.

differential fault

See: scissor fault.

differential grinding

Application of comminution in such a way as to accentuate differences in grindability between the various mineral species in the ore. Therefore, in suitable cases, the relatively tough mineral particles remain coarse while the more friable ones are finely ground.

differential pressure flowmeter

An instrument for measuring water and water-ore slurries in ore dressing and coal dressing processes.

differential pumping engine

A compound direct-acting pumping engine, generally of the horizontal class.

differential settlement

Nonuniform settlement; the uneven lowering of different parts of an engineering structure, often resulting in damage to the structure. See also: settlement.

differential thermal analysis

a. A method of analyzing a variety of minerals, esp. clays and other aluminiferous minerals. The method is based upon the fact that the application of heat to many minerals causes certain chemical and physical changes and is reflected in endothermic and exothermic reactions. By comparing the changes in temperature of a mineral heated at a definite rate with that of a thermally inert substance (alumina, for example) heated under the same conditions, a curve or pattern is obtained that is characteristic of the particular mineral under examination.

b. Thermal analysis carried out by uniformly heating or cooling a sample that undergoes chemical and physical changes, while simultaneously heating or cooling in identical fashion a reference material that undergoes no changes. The temperature difference between the sample and the reference material is measured as a function of the temperature of the reference material. Abbrev: DTA.

differential weathering

Weathering that occurs at different rates, as a result of variations in composition and resistance of a rock or differences in intensity of weathering, and usually resulting in an uneven surface where more resistant material protrudes above softer or less resistant parts. Syn: selective weathering.


A rock formed as a result of magmatic differentiation.


Said of an igneous intrusion in which there is more than one rock type, owing to differentiation.


See: magmatic differentiation. CF: assimilation.


The cooperative scattering of any electromagnetic radiation where it encounters an obstacle, esp. the edge of an obstacle, resulting in constructive and destructive interference. Also, a single event resulting from constructive interference. See also: optical diffraction; X-ray diffraction. Syn: wave diffraction. CF: reflection.

diffraction grating

An optical device having equidistant fine lines (on the order of wavelengths of visible light) scribed on glass for transmission, or on metal for reflection diffraction, of monochromatic light.

diffraction pattern

a. Diffracted X-rays recorded on film, giving a means of identification of a powder.

b. A record of diffracted X-rays on film or paper showing angles of diffraction of monochromatic radiation; used for characterization or identification of a crystalline substance. CF: Laue photograph.


a. The inner shell and water passages of a centrifugal pump.

b. See: evase.

diffuser chamber

A chamber in a turbine pump consisting of a number of fixed blades. On leaving the impeller, the water is guided outward by these blades with the minimum of eddying and swirling. See also: turbine pump.

diffusion of gases

The property that all gases possess of mixing with each other.


The relative rate of flow per unit area of a particular constituent of a mixture divided by the gradient of composition, temperature, or other property considered to be causing the diffusion.