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

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dachiardite

A monoclinic mineral, (Ca,Na (sub 2) ,K (sub 2) ) (sub 5) Al (sub 10) Si (sub 38) O (sub 96) .25H (sub 2) O ; zeolite group; in a pegmatite at San Piero, Elba, Italy.

dacite

A fine-grained extrusive rock with the same general composition as andesite, but having a less calcic plagioclase and more quartz; according to many, it is the extrusive equivalent of granodiorite. Syn: quartz andesite. The name, given by Stache in 1863, is from the ancient Roman province of Dacia (now part of Romania).

dacker

Eng. Insufficient ventilation of a mine; dead air.

dactylitic

A term applied to a rock texture produced by a symplectic intergrowth, in which one mineral is penetrated by fingerlike projections from another mineral; also, said of a rock exhibiting such texture. See also: dactylotype intergrowth; symplectic.

dactylotype

A textural term applied by Shand in 1906 to the intergrowth of sodalite with orthoclase in borolanite and its associates. The sodalite is altered to pinitic mica and appears in threadlike or vermicular aggregates closely packed in a matrix of orthoclase.

dactylotype intergrowth

a. A mineral intergrowth in which thin successive layers resemble a fingerprint pattern, as in some orthoclase-nepheline intergrowths.

b. A symplectic intergrowth in which fingerlike projections of one mineral penetrate another. See also: dactylitic.

dad

N. of Eng. In coal mining, to mix (combustible gases) with atmospheric air to such an extent that the mixture is incapable of exploding. Also called dash. See also: dashing.

dadding

The circulation, control, and utilization of air produced by the fan to ventilate the mine workings. See also: circulation of air.

Daelen mill

An early type of universal rolling mill provided with both vertical and horizontal rolls so that a part could be rolled on all sides in one operation.

Daeves's reagent

An etchant used to distinguish carbides in chromium steels and tungstides in high-speed steels. The solution contains 20 g of potassium ferricyanide and 10 g of potassium hydroxide in 100 mL of water.

dahllite

A resinous, yellowish-white carbonate-apatite mineral or association sometimes occurring as concretionary spherulites. Now called carbonate-hydroxylapatite.

Dahlstrom's Formula

Classification through the hydrocyclone.

dakeite

See: schroeckingerite.

dam gradation

See: contragradation.

damkjernite

A hypabyssal rock composed of phenocrysts of biotite and titanaugite in a fine-grained groundmass of pyroxene, biotite, perovskite, and magnetite, with interstitial nepheline, microcline, and calcite. The name, given by Broegger in 1921, is for the locality Damkjern (or Damtjern), Fen complex, Norway. Also spelled: damtjernite.

damp

Any mine gas, or mixture of gases, particularly those deficient in oxygen. Damp is probably derived from the German dampf, meaning a fog or vapor. See also: afterdamp; blackdamp; chokedamp; combustible gases; firedamp; stinkdamp; white damp.

damping

a. In seismology, a resistance, contrary to friction, independent of the nature of the contacting surface. Being proportional to the speed of motion, it diminishes with the latter to nothing.

b. A force opposing vibration, damping acts to decrease the amplitudes of successive free vibrations. Damping may result from internal friction within the system, from air resistance, or from mechanical or magnetic absorbers. CF: attenuation. c. The loss of amplitude of an oscillation, owing to absorption. See also: critical damping; damping factor.

damping constant

In damped seismographs, this term is by definition equal to one-half the ratio of the damping resistance (force per unit velocity) to the moving mass. It has the dimensions of a frequency.

damping down

In pyrometallurgy, reduction of air supply to a furnace, to lower temperature or reduce working rate.

damping factor

The ratio of the observed damping to that required for critical damping. See also: damping.

damping ratio

a. The damping ratio for a system with viscous damping is the ratio of the actual damping coefficient to the critical damping coefficient.

b. The ratio of two equiphase peak amplitudes within one period of a damped seismograph or seismometer. The ratio is always greater than unity since the greater amplitude is divided by the succeeding amplitude.

dam plate

In a blast furnace, the cast-iron plate that supports the dam or dam stone in front.

damp sheet

S. Staff. A large sheet placed as a curtain or partition across a gate road to stop and turn an air current.

dampy

Mid. Mine air mixed with so much carbonic acid gas as to cause the lights to burn badly or to go out.

damsite testing

Boreholes drilled to determine petrological and structural features of the rock or overburden materials at or near the area on which the foundations of a dam will rest.

dam stone

The wall of firebrick or stone enclosing the front of the hearth in a blast furnace.

dan

a. Mid. A tub or barrel, sometimes with and sometimes without wheels, in which mine water is conveyed along underground roadways to the sump or raised to the surface.

b. A small box or sledge for carrying coal or waste in a mine.

danaite

A cobaltoan variety of arsenopyrite.

danalite

An isometric mineral, Fe (sub 4) Be (sub 3) (SiO (sub 4) ) (sub 3) S ; vitreoresinous; forms series with genthelvite and helvite.

danburite

An orthorhombic mineral, CaB (sub 2) Si (sub 2) O (sub 8) ; resembles topaz in habit, appearance, and properties; in marbles, low-temperature veins, and placers.

Danian

Lowermost Paleocene or uppermost Cretaceous.

Daniell cell

A primary cell, with a constant electromotive force of about 1.1 V, having as its electrodes: (1) copper in a copper sulfate solution, and (2) zinc in dilute sulfuric acid or zinc sulfate--the two solutions being separated by a porous partition.

Danish flint pebbles

Pebbles for grinding media, of superior hardness, toughness, and uniformity, found on the shores of Greenland.

danks' puddler

A revolving mechanical puddler. See also: puddling.

dannemorite

A monoclinic mineral, Mn (sub 2) (Fe (super 2+) , Mg) (sub 5) Si (sub 8) O (sub 22) (OH) (sub 2) ; amphibole group; has Fe (super 2+) /(Mg + Fe (super 2+) ) = 0.5 to 1.0 ; columnar or fibrous; at Dannemora, Sweden.

d'Ansite

An isometric mineral, Na (sub 21) Mg(SO (sub 4) ) (sub 10) Cl (sub 3) .

dant

a. Soft sooty coal found in face and back slips or cleats; fine slack coal.

b. To reduce, as a metal, to a lower temper.

daourite

A pink variety of elbaite.

dap

a. A notch cut in a timber to receive another timber.

b. See: legs.

daphnite

A magnesian variety of chamosite.

darapskite

A monoclinic mineral, Na (sub 3) (SO (sub 4) )(NO (sub 3) ).H (sub 2) O .

Darby process

A method of carburizing open hearth steel that consists of treating the molten steel with carbon in the form of charcoal, graphite, or coke.

darg

a. A specified day's work, usually at the coal face. See also: stint.

b. A task, or a fixed quantity of coal, agreed to be produced per shift for a certain price. c. Scot. To work by the day. d. A north German name for meadow or moor peat buried under clay. e. Peat formed from marine vegetation.

dark ground

Indirect illumination of stage of microscope, causing objects to be brightly displayed by oblique rays against a dark background.

dark mica

See: biotite.

dark mineral

Any one of a group of rock-forming minerals that are dark-colored in thin section, e.g., biotite, hornblende, augite.

dark red silver ore

See: pyrargyrite.

dark ruby silver

See: pyrargyrite.

dark sulfur

Crude, dark-colored sulfur containing up to 1% oil or carbonaceous material.

darlingite

A variety of lydian stone from Victoria, Australia.

dashing

Eng. Increasing the amount of air in mines to prevent explosions of mine gases. See also: dad.

dashkesanite

A chlorine-rich variety of hastingsite.

dashpot

a. An appliance for damping out vibration. It consists of a piston attached to the object to be damped and fitting loosely in a cylinder of oil. See also: hydrabrake retarder.

b. A similar device for closing the valves in a Corliss engine, actuated by atmospheric pressure or by a contained spring.

dasymeter

An instrument for testing the density of gases. It consists of a thin glass globe, which is weighed in the gas or gases under observation, and then in an atmosphere of known density.

dating

Age determination of naturally occurrring substances or relicts by any of a variety of methods based on the amount of change, happening at a constant measurable rate, in a component. The changes may be chemical, or induced or spontaneous nuclear, and may take place over a period of time.

datolite

A monoclinic mineral, CaBSiO (sub 4) (OH) ; gadolinite group; in cracks and cavities in diabase or basalt; may be used as a minor gem. Also spelled datholite. Syn: humboldtite; dystome spar.

datum

a. The top or bottom of a bed of rock, or any other surface, on which structure contours are drawn.

b. Sea-level datum.--Pl: datums. c. Any numerical or geometric quantity or value that serves as a base or reference for other quantities or values; any fixed or assumed position or element (such as a point, line, or surface) in relation to which others are determined, such as a level surface to which depths or heights are referred in leveling. Pl: datums; the plural data is used for a group of statistical or inclusive references, such as geographic data for a list of latitudes and longitudes. See also: datum plane; geoid.

datum level

Any level surface, such as mean sea level, used as a reference from which elevations are reckoned; a datum plane.

datum plane

a. A horizontal plane used as a reference from which to reckon heights or depths.

b. A permanently established horizontal plane, surface, or level to which soundings, ground elevations, water-surface elevations, and tidal data are referred; e.g., mean sea level is a common datum plane used in topographic mapping. Syn: datum level; reference level; reference plane. See also: datum.

datum water level

a. The level at which water is first struck in a shaft sunk on a reef or gutter.

b. Ground or surface water level used as a reference for all other measurements.

dauberite

See: zippeite.

daugh

a. Scot. The floor of a coal seam or where holing is done.

b. Underclay; soft fireclay.

daughter element

The element formed when a radioactive element undergoes radioactive decay. The latter is called the parent. The daughter may or may not be radioactive.

Dauphine diamond

Rock crystal variety of quartz.

Dauphine law

The law governing a twinning observed in the hexagonal system commonly shown by quartz in which two righthand or two lefthand crystals interpenetrate after one has revolved 180 degrees about the twinning axis.

Dauphine twinning

Transformation twinning about the [0001] direction with an irregular contact surface in quartz. Syn: electrical twinning.

D'Autriche Method

A method of geometrically determining the detonation velocity of an explosive material by using a lead witness plate and detonating cord ignited by the test explosive.

Dautriche test

See: velocity of detonation.

davidite

A trigonal mineral, (La,Ce)(Y,U,Fe)(Ti,Fe) (sub 20) (O,OH) (sub 38) ; crichtonite group; radioactive; metamict; in high-temperature hydrothermal veins, pegmatites, and mafic igneous rocks; occurs in all stages of intergrowth and exsolution with ilmenite and hematite, and is an ore of uranium. Syn: ferutile.

davidsonite

A greenish-yellow variety of beryl.

Davis bit

See: Davis cutter bit.

Davis calyx drill

A rotary drill similar to the diamond core drill except that the annular groove is cut either by a steel chisel or by a plain hollow rod using chilled shot. When the core is of sufficient length to be withdrawn, some grit is added to the mud flush, which becomes wedged tightly between the core and base of the barrel. When the rods are raised the core is broken off and brought to the surface.

Davis cutter bit

An annular-shaped, sawtoothlike bit used on shot drills to cut core in soft formations in which shot is ineffective as a cutting medium. Syn: Davis bit.

Davis furnace

A long, one-hearth reverberatory furnace, heated by lateral fireplaces for roasting sulfide ore.

Davis magnetic tester

An instrument for testing the magnetic content of ores and for checking the efficiency of wet magnetic separators recovering magnetite and ferrosilicon in heavy-media processes.

davisonite

A mixture of crandallite and an apatite. Syn: dennisonite.

Davis wheel

A railway tire consisting of a soft plate and boss, and a wear- resistant tread of water-toughened manganese steel, cast integrally within.

davreuxite

A monoclinic mineral, MnAl (sub 6) Si (sub 4) O (sub 17) (OH) (sub 2) .

Davy lamp

A safety lamp invented by Sir Humphrey Davy in 1815 for the protection of coal miners. Its safety feature consisted of a fine-wire gauze enclosing the flame to keep it from coming in contact with mine gas. See also: flame safety lamp; safety lamp.

davyne

A hexagonal mineral, (Na,Ca,K) (sub 8) Al (sub 6) Si (sub 6) O (sub 24) (Cl,SO (sub 4) ,CO (sub 3) ) (sub 2) ; cancrinite group; vitreous to pearly. Also spelled davina.

dawsonite

An orthorhombic mineral, NaAl(CO (sub 3) )(OH) (sub 2) ; white; forms thin incrustations of radiating bladed crystals.

day

a. A term used to signify the surface; e.g., driven to day, meaning to daylight, therefore to the surface.

b. Wales. The surface of the ground over a mine. c. In mining, generally a period of 8 h for work on the three-shift system, or 24 h if referring to the output or to machinery.

day box

See: powder chest.

day coal

The topmost stratum of coal; so called from its being nearest to daylight.

daylight

a. When an underground mine working meets the surface it is said to daylight.

b. The maximum clear distance between the pressing surfaces of a hydraulic press with the surfaces in their usable open position. Where a bolster is supplied, it shall be considered the pressing surface.

dc (direct chill) casting

A continuous method of making ingots or billets for sheet or extrusion by pouring the metal into a short mold. The base of the mold is a platform that is gradually lowered while the metal solidifies, the frozen shell of metal acting as a retainer for the liquid metal below the wall of the mold. The ingot is usually cooled by the impingement of water directly on the mold or on the walls of the solid metal as it is lowered. The length of the ingot is limited by the depth to which the platform can be lowered; therefore, it is often called semicontinuous casting.

deactivation

In froth flotation, treatment of one or more species of mineral particles to reduce their tendency to float.

dead

a. Said of a mine, vein, or piece of ground that is unproductive.

b. Said of coal that is under no pressure, does not warp and burst, and makes no sound. CF: alive. c. In economic geology, said of an economically valueless area, in contrast to a quick area or ore; barren ground.

dead air

a. Stagnant air.

b. The air of a mine when it contains carbonic acid gas (blackdamp), or when ventilation is sluggish.

dead band

In flotation, the range through which an input can be varied without initiating response.

dead bed

Unproductive stratum or vein as opposed to bearing or quick bed. Syn: dead vein. See also: barren ground.

dead-burned

a. The state of a basic refractory material resulting from a heat treatment that yields a product resistant to atmospheric hydration or recombination with carbon dioxide.

b. Completely calcined.

dead-burned dolomite

A refractory product, CaO.MgO, produced by calcination of dolomite or dolomitic limestone.

dead-burned magnesia

A sintered product consisting mainly of magnesia in the form of dense, weather-stable refractory granules.

dead burnt

Calcination of limestone, dolomite, or magnesite to the point where associated clay vitrifies and reduces slaking quality.

dead chert

See: chalky chert.

dead end

a. An entry, gangway, level, or other mine passage extending beyond the mine workings into solid coal or ore; a stub. Syn: stub entry.

b. Underground passageway either blocked or not holed through. c. The unworked end of a drift or working. d. An unventilated underground mine passage extending some distance beyond other mine workings into solid rock. e. A term used in coal mining for the termination of all electric wiring (except cables to equipment) outby the last crosscut where ample ventilation will reduce the possibility of an electric arc causing an explosion. f. The end of a drilling line or cable made fast to some stationary part of the drill rig or to a deadman.

dead ground

a. Rock in a mine that, although producing no ore, requires removal in order to get to productive ground.

b. In mining subsidence, ground that has settled and no further movement is expected. c. Portions of ore deposit too low in value to repay exploitation. CF: barren ground.

deadhead

a. To return to the commencement of a cut without excavating; usually for the commencement of a new cut after completion of its predecessor.

b. An extra length given to a cast object, as a cannon, to put pressure on the molten metal below so that dross and gases may rise into it; a sullage piece; a sinking head. c. That part of a casting filling up the ingate; a sprue. d. Can. Logs forced into the bottom of a waterway during timber drives.

deadheading

Traveling without load, except from the dumping area to the loading point.

dead hole

a. One that extends into solid coal beyond the part that can be broken by the maximum safe charge of explosive.

b. A shothole so placed that its width at the point (toe), measured at right angles to the drill hole, is so great that the heel is not strong enough to at least balance the resistance at the point (toe). c. A shallow hole in an iron casting.

deadline

a. A row of marked empty powder kegs or other danger signal placed by the fireboss to warn miners not to enter workings containing gas.

b. The part of a block-and-tackle cable from the traveling block to the deadline anchor.

deadline anchor

The fixed point on a drill rig or deadman to which a deadline of a block and tackle is attached.

dead load

The downward pressure on a structure caused by gravity only, such as the weight of a long string of drill rods suspended from the sheave in a drill derrick. Syn: static load. See also: live load.

dead lode

A lode not containing valuable minerals in paying quantity.

deadman

a. A wooden block used to guard the mouth of a mine against runaway cars.

b. A buried log, timber, concrete block, or the like serving as an anchor to which a pulling line can be attached.

dead pressing

Desensitizing of an explosive, caused by excessive pressure or high density.

dead quartz

Quartz carrying no valuable mineral.

dead rent

Of a mineral lease, the rent that must be paid whether or not minerals are being extracted.

dead roast

a. A roasting process for complete elimination of sulfur or other volatiles. Syn: sweet roast.

b. In fluidization roasting, restriction of entering air to permit oxidation of sulfides, while not allowing process to proceed to any marked degree of sulfate roasting.

dead roasting

Sulfide ores are dead roasted when all the sulfur possible to drive off by roasting has been eliminated.

dead rock

The material removed in the opening of a mine that is of no value for milling purposes. Waste rock.

dead soft

The state of metal that has been fully annealed.

dead steel

a. Fully killed steel, which sinks quietly in the ingot mold during solidification.

b. Steel that fails to respond to heat treatment because it has been worked at excessively high temperatures; e.g., 1,300 to 1,350 degrees C.

dead time

In flotation, the interval of time between initiation of an input and the start of the resulting response. It may be qualified as effective if extended to the start of the buildup time, theoretical if the dead band is negligible, and apparent if it includes the time spent with an appreciable dead band.

dead true

A core barrel or drill rod that does not oscillate or vibrate when rotated at high speed is said to be dead true.

dead vein

See: dead bed.

dead veins

Veins barren of economic minerals.

deadweight

a. The weight of a vehicle or carrier itself as distinguished from carried or live load.

b. The difference, in tons, between a ship's displacement at load draft and light draft. It comprises cargo, bunkers, stores, fresh water, etc.

dead work

a. Work that is not directly productive--the removal of rock, debris, or other material that is not directly productive of coal--though it may be necessary for exploration and future production. Unfinished work. See also: stonework.

b. Unproductive or stone work; the handling of stone or dirt as a preliminary step to winning and working the coal seam. The aim is to keep the dead work per yard of face or ton of coal to the minimum practicable figure. See also: unproductive development. c. Any kind of miner's work other than actual coal getting and transport. d. Exploratory or preparatory work, such as cleaning falls of roof, removing rock, etc., during which little or no coal is secured. e. The development of a mine when no ore is being raised. f. Work done by a contractor not provided for in the yardage or tonnage contract rates. g. S. Afr. Necessary work to reach and exploit the valuable portions of the mine. Shaft sinking, crosscutting, driving of levels, etc., belong to dead work.

dead zone

That part of the mined strata that has completely settled down after subsidence.

dealer

An operator on the stock exchange who buys and sells on his or her own account and who makes a profit from differences in prices rather than from commissions.

debacle

a. A breakup on a river, esp. on the great rivers of the former U.S.S.R. and of North America.

b. The rush of water, broken ice, and debris in a stream immediately following a breakup. Syn: ice run. c. Any sudden, violent, destructive flood, deluge, or rush of water that breaks down opposing barriers and sweeps before it debris of all kinds.---Etymol: French debacle.

Deblanchol rotary furnace

A cylindrical refractory-lined shell, provided with a gas flue leading to a recuperator at one end, and a fuel and air port at the other. Air for combustion is preheated in the recuperator, and oil firing is adopted. The furnace may be used for melting gray iron and nonferrous metals.

debris

Any surficial accumulation of loose material detached from rock masses by chemical and mechanical means, as by decay and disintegration. It consists of rock fragments, soil material, and sometimes organic matter. The term is often used synonymously with detritus, although debris has a broader connotation. Etymol: French debris. Pl: debris. Syn: rock waste.

debris bag

A dirt-filled bag used for pack walls and chocks. See also: sandbag.

debris cone

See: alluvial cone.

debris deposits

Refuse from hydraulic mining operations, tailings.

decalescence

A phenomenon associated with the transformation of alpha iron to gamma iron on the heating (superheating) of iron or steel, revealed by the darkening of the metal surface owing to the sudden decrease in temperature caused by the fast absorption of the latent heat of transformation. Syn: point of decalescence.

decalescence point

See: critical point.

decantation

The settlement of a solid from a liquid, and removal of the clear liquid.

decanter

a. An apparatus for sorting and classifying tailings from gold-washing operations.

b. A vessel used to decant or to receive decanted liquids.

decarbonation

The process of driving off carbon dioxide from a carbonate mineral, e.g., magesite, MgCO (sub 3) , to form periclase, MgO .

decarburization

The loss of carbon from the surface of a ferrous alloy as a result of heating in a medium that reacts with the carbon at the surface.

decay

The general disaggregation of rocks; it includes the effects of both the chemical and mechanical agents of weathering with, however, a stress on the chemical effects.

decay distance

The distance between an area of wave generation and a point of passage of the resulting waves outside the area.

dechenite

Natural PbV (sub 2) O (sub 6) ; not established as a valid mineral species.

decibar

The pressure exerted per square centimeter by a column of sea water 1 m tall is approx. 1 decibar. The depth in meters and the pressure in decibars, therefore, are expressed by nearly the same numerical value.

decibel

The unit for measuring sound intensity.

decision function

Rule made to control a specific sampling investigation, which defines the point at which no further observations are to be made, and the nature of the decision that is to be agreed upon. In a series of sampling operations, each successive decision function depends on those that have preceded it.

deck

a. One of the separate compartments or platforms into which a cage is divided to hold cars. See also: multideck cage.

b. The surface of a concentrating table. c. The refractory top of a car used in a tunnel kiln or bogie kiln.

deck charge

a. A charge that is divided into several separate components along a quarry borehole. CF: columnar charge.

b. A charge separated by stemming.

decke

See: nappe.

decking

a. The operation of changing the tubs on a cage at top and bottom of a shaft. Also called caging.

b. Separating charges of explosives by inert material and placing a primer in each charge.

decking level

The level at which a cage comes to rest at the pit head and pit bottom for unloading and loading mine cars.

deck load

A charge of dynamite spaced well apart in a borehole and fired by separate primers or by a detonating cord.

deck loading

A method of loading blast holes in which the explosive charges, called decks or deck charges, in the same hole are separated by stemming, air cushion, or a plug.

deck screens

Two or more screens, usually of the vibrating type, placed one above the other for successive processing of the same run of material.

declaratory statement

In practical mining operations, a term applied to the statutory certificate of location, and a certificate or statement of the location, containing a description of the mining claim, verified by the oath of the locator, performing, when recorded, a permanent function. It is the beginning of the locator's paper title, is the first muniment of such title, and is constructive notice to all the world.

declared efficiency

The efficiency assigned by the maker under certain specified conditions.

declination

a. The horizontal angle in any given location between true north and magnetic north; it is one of the magnetic elements. Syn: variation; magnetic variation.

b. Angular elevation of a star above celestial equator when truly north of observer. c. Angular deviation of magnetic compass from true north, observed in conditions where no local deviation affects it. d. The angular change in the course of a borehole induced by deflection techniques, usually expressed in degrees. e. Sometimes a syn. for inclination. See also: inclination.

declination maps

Maps on which isogonic lines are shown.

declining conveyor

A conveyor transporting down a slope. See also: retarding conveyor.

decollement

Detachment structure of strata owing to deformation, resulting in independent styles of deformation in the rocks above and below. It is associated with folding and with overthrusting. Etymol: French, unsticking, detachment. CF: disharmonic folding. Syn: detachment.

decomposing furnace

A furnace used in the conversion of common salt into sulfate of soda, aided by the action of sulfuric acid.

decomposition

See: chemical weathering.

decompression

The process of reducing high air pressure gradually enough so as not to injure people who have been working in it.

decompression illness

A condition among underwater workers and mine rescue teams that is caused by ascending too quickly from deep dives.

decompression sickness

See: aeroembolism.

decorative stone

a. A term sometimes used alternately with ornamental stone.

b. Natural material used as architectural trimmings in columns, fireplaces, and store fronts; may be set in silver- or gold-filled jewelry, as curio stones; e.g., malachite and marble. CF: gemstone.

decoupling

A method for decreasing the ground motion generated by an underground explosion. The method involves the firing of the explosive in the center of an underground cavity so that the surrounding medium is not in close proximity to the explosive.

decrepitate

a. To roast or calcine (as salt) so as to cause crackling or until crackling stops.

b. A mineral is said to decrepitate when it flies to pieces with a crackling noise on being heated.

decrepitation

a. Method of differential disintegration of closely sized mineral, part of which explodes and is separable by finer screening.

b. The breaking up with a crackling noise of mineral substances upon exposure to heat, as when rock salt is thrown into fire. c. An obsolete method of tunneling, called fire setting.

decussate texture

A microtexture in metamorphosed rocks, in which axes of contiguous crystals lie in diverse, crisscross directions that are not random but rather are part of a definite mechanical expedient for minimizing internal stress. It is most noticeable in rocks composed largely of minerals with a flaky or columnar habit.

dedolomitization

a. A process resulting from metamorphism, wherein part or all of the magnesium in a dolomite or dolomitic limestone is used for the formation of magnesium oxides, hydroxides, and silicates (e.g., brucite, forsterite) and resulting in an enrichment in calcite.

b. Diagenetic or weathering processes wherein dolomite is replaced by calcite.

dedusting

A cleaning process in which dust and other fine impurities are removed. Dedusting is accomplished both by pneumatic means and by dry screening. Syn: aspirating.

deenergize

To disconnect any circuit or device from the source of power.

deep

a. Workings below the level of the pit bottom or main levels extending therefrom.

b. Forest of Dean; Lanc. A vein, seam, mine, or bed of coal or ironstone. c. Term used to designate ocean bottom depressions of great depth, usually deeper than 6,000 m.

deep cell count

A method for examining the mineral particle content of drilling water. In this method, a glass cell is filled with the water, a little acid is added, and the sample is placed under a microscope. Dark ground illumination is used, which shows up the suspended particles. The number of these is counted, and this number, multiplied by a factor, gives the number of particles per cubic centimeter.

deep coal

Eng. Coal seams lying at a depth of 1,800 ft (549 m) or more below the surface.

deep drawing

The process of cold working or drawing a sheet of strip metal, by means of dies, into shapes involving considerable plastic distortion of the metal; e.g., automobile mudguards, electrical fittings, etc.

deep hole

In continuous wire-line core drilling, a term applied to boreholes 3,000 ft (915 m) or more in depth.

deep-hole blasting

Blasting a quarry or opencast face by using small- or medium-diameter holes drilled from top to bottom of the face.

deep lead

Alluvial deposit of gold or tin stone buried below a considerable thickness of soil or rock. CF: lead.

deep level

a. Trans. The first mining properties developed from the surface were stopped from trespassing beyond their side lines projected downward. The next mine on the dip of the lode became known as the "deep-level" mine or "deep."

b. S. Afr. The distinction of deep level and ultradeep level is a vague one, and has changed with the times. Ultradeep is now a mining level at a vertical depth of 9,000 ft ( 2.7 km) and over.

deep mining

The exploitation of coal or mineral deposits by underground mining methods. "Deep" is often interpreted as meaning 5,000 ft (1.5 km) or more, where stresses are high enough to cause sloughing of development openings, not to mention walls and faces in stopes. However, tectonic horizontal stresses are greater than gravitational force in many areas. Hence deep conditions can exist at lesser depths. Indeed, severe rock bursting caused the closure of a Canadian mine operating at depths of 500 to 700 ft (152 to 213 m). Also, rocks with low strength will produce deep failure patterns at modest depths, e.g., in Saskatchewan potash mines.

deep placer

A sandy or gravelly bed or bottom of an ancient stream covered by lava.

deep scattering layer

Applied to widespread strata in the ocean that scatter or return vertically directed sound as in echo depth sounding. These layers, which are evidently of biological origin, are located at depths ranging from 150 to 200 fathoms (274 to 366 m) during the day, with most of them migrating to or near the surface during the night. Abbrev: dsl.

deep seated

See: plutonic.

deep-seated deposit

An ore deposit formed at an estimated depth of 12,000 ft (3.66 km) or more, at temperatures ranging from 300 to 575 degrees C; e.g., the tin deposits of Cornwall, England. The deposits are commonly tubular or veinlike in form, though some are irregular in shape.

deep-sea terrace

The benchlike feature bordering an elevation of the deep-sea floor at depths greater than 300 fathoms (1,800 ft or 549 m).

deepside

The working of 5 to 10 yd (4.6 to 9.1 m) of the coal seam on the dip side of an advance gate. It gives some protection from crush along the rib side and also accommodates dirt from the gate instead of conveying it to the surface. See also: self-stowing gate.

deep sinker

Aust. A tall drinking glass; also the drink it contains, so called in fanciful allusion to the shaft of a mine.

deep well

A borehole put down through an upper impervious bed into a lower pervious one, from which a supply of water is obtained. See also: well.

deep-well pump

a. Any kind of pump delivering from a well, shaft, or borehole.

b. An electrically driven pump located at the low point in the mine to discharge the water accumulation to the surface. c. Consists of a series of centrifugal pump impellers mounted on a single rotating shaft. The casings are termed bowls and the impellers are of the axial or mixed-flow type. Available in capacities ranging from 25 to 10,000 gal/min (94.6 to 37,854 L/min). It can be used in wells from 25 to 800 ft (7.6 to 244 m) in depth and from 6 to 24 in (15.2 to 61 cm) in diameter.

deep-well turbine

A simple type of vertical centrifugal pump having one or more stages or bowls, which are supported from the motor head on the surface by means of screwed or flanged column pipe sections, each usually 10 ft (3 m) long. The line shafting from the motor to the impellers is sectional to correspond with the column section, and may operate in a sectional extra-heavy enclosing tube if oil is used as a lubricant, or may be exposed to the water when the pump is built to be water-lubricated.

deep winding

a. Broadly, shaft winding from depths of about 3,000 ft (915 m) and deeper (coal mining). In the case of shafts deeper than about 5,000 ft or 1.52 km (gold and metal mining), two-stage hoisting may be used. See also: winding.

b. Hoisting from depths below 5,000 ft in one lift. c. Deep hoisting.

Deerparkian

Middle Lower Devonian.

deficient coal

Ark. Coal more difficult to mine than the standard, and for which the miners are paid an extra price.

deflagrate

To burn; burst into flame; specif., to burn rapidly with a sudden evolution of flame and vapor.

deflagrating mixture

An explosively combustible mixture, as one containing niter.

deflagration

An explosive reaction such as a rapid combustion that moves through an explosive material at a velocity less than the speed of sound in the material.

deflation

The removal of loose dry particles by the wind, as along a sand-dune coast or in a desert; a form of wind erosion.

deflecting plug

a. See: base plug.

b. Sometimes used by petroleum drillers as a syn. for deflecting wedge.

deflecting wedge

A class of devices intentionally placed in a borehole to change its course. All such devices are basically long, tapered, concave metal plugs that can be set at a predetermined point and bearing in a borehole to deflect or change its course. Also called correcting wedge, deflecting plug, deflection wedge, Hall-Rowe wedge, spade-end wedge, Thompson wedge. See also: correcting wedge; wedge.

deflection

A change in the intended course of a borehole produced intentionally or unintentionally by various conditions encountered in the drill hole or by the operational characteristics of the drilling equipment used. Syn: deviation.

deflection angle

a. The angular change in the course of a borehole produced accidentally or intentionally.

b. A vertical angle, measured in the vertical plane containing the flight line, by which the datum of any model in a stereotriangulated strip departs from the datum of the preceding model. c. A horizontal angle measured from the forward prolongation of the preceding line to the following line; the angle between one survey line and the extension of another survey line that meets it. A deflection angle to the right is positive; one to the left is negative.

deflection bit

A taper bit, generally a bullnose type, used to drill down past the deflecting wedge when deflecting a borehole.

deflection dial

The load-indicating gage on a penetrometer, which is a soil-testing device used to determine some of the load-bearing characteristics of silt and sandy soils. See also: cone penetrator.

deflection plug

See: base plug.

deflection point

Point of deflection on a refraction time-versus-distance graph separating two segments that correspond to different wave paths.

deflection wedge

A wedge-shaped tool inserted in a borehole to direct the bit along a prescribed course. Also called whipstock (undesirable usage). See also: deflecting wedge.

deflectometer

An instrument for gaging any deflections of a structure.

deflector

A device across the path of a conveyor placed at the correct angle to deflect objects or discharge bulk material. Also called a plow.

deflector sheet

A sheet of brattice or other material erected in a roadway or face to remove a combustible gases layer. It is usually set at an angle of about 45 degrees from the horizontal and inclined in the direction of airflow. See also: pocket of gas.

deflector-wedge ring

An annular steel ring attached to the upper end of a deflecting wedge, having a slightly smaller diameter than that of the borehole in which the wedge is inserted, serving as a stabilizing ring to hold and center the wedge in the borehole. Also called rose ring.

deflocculant

a. Any organic or inorganic material that is used as an electrolyte to disperse nonmetallic or metallic particles in a liquid, (i.e., basic materials such as calgonate, sodium silicate, soda ash, etc., are used as deflocculants in clay slips).

b. A basic material such as sodium carbonate or sodium silicate, used to deflocculate. Syn: deflocculating agent.

deflocculate

a. To disperse a clay suspension so that it has little tendency to settle and has a low viscosity.

b. To break up from a flocculated state; to convert into very fine particles. CF: peptize.

deflocculating

a. The thinning of the consistency of a slip by adding a suitable electrolyte.

b. The process of making clay slips or suspension using electrolytes or deflocculants.

deflocculating agent

An agent that prevents fine soil particles or clay particles in suspension from coalescing to form flocs. Syn: deflocculant; dispersing agent.

deflocculation

A state of colloidal suspension in which the individual particles are separate from one another, this condition being maintained by the attraction of the particles for the dispersing medium (for example, hydration) or by the assumption of like electrical charges by the particles, thus resulting in their mutual repulsion, or both. It is generally possible to deflocculate a gel to such an extent that it loses its gel strength entirely, thus becoming a Newtonian fluid, in which case it is known as a sol. The relative contribution of hydration and electrostatic repulsion to the deflocculation of a suspension accounts in large measure for the wide variation in viscosities and gel strengths of suspensions partially flocculated by different means; as, e.g., a partial flocculation of drilling fluid by cement on one hand, and by salt water on the other. Some suspensions can be deflocculated repeatedly by mechanical agitation alone, thus giving a reversible gel-sol, sol-gel transformation known as thixotropy.

deformation

a. A general term for the process of folding, faulting, shearing, compression, or extension of the rocks as a result of various Earth forces.

b. See: strain.

deformation bands

Parts of a crystal that have rotated differently during deformation to produce bands of varied orientation within individual grains.

deformed crossbedding

Crossbedding with foresets overturned or buckled in the down current direction, usually prior to deposition of the overlying bed. Foreset dip angle may also be altered by subsequent tectonic folding.

deformed crystal

A crystal bent or twisted out of its normal shape, so that the angle between its crystal faces may differ widely from those on the regular form. See also: distorted crystal.

defrother

An agent, e.g., butanol, that destroys or inhibits froth.

degasification

Progressive loss of gases in a substance leading to the formation of a more condensed product. Applied primarily to the formation of solid bitumens from liquid bitumens, but also used in connection with coal formation.

degasifier

A substance that can be added to molten metal to remove soluble gases that might otherwise be occluded or entrapped in the metal during solidification.

degassing

a. Removing gases from liquids or solids.

b. In pyrometallurgy, addition of deoxidants (phosphorus, aluminum, silicon, etc.) to remove hydrogen from molten metals before casting.

degassing equipment

a. The equipment for extracting gas from an oil-well drilling fluid. The presence of gas reduces the density of the fluid.

b. The pumps and equipment used in methane drainage.

degaussing

Method of demagnetization in which a substance is passed through a coil that carries alternating current of progressively diminishing strength.

degradation

a. The general lowering of the surface of the land by erosion, esp. by the removal of material through the action of flowing water.

b. Breakage of coal incidental to mining, handling, transport, or storage. c. The excessive crushing of coal during cutting, loading, and transportation. All face machines cause degradation, and this has become a problem at collieries where the market calls for the larger sizes. The degradation of a coking coal is of lesser importance. See also: gradation; fragmentation. CF: aggradation. Syn: breakage of coal.

degradation screens

Screens used for removing the small sizes, caused by breakage in handling, from sized coal just before it is loaded for shipment. Degradation screening is usually necessary where a sized coal is picked, mechanically cleaned, stored, conveyed, or otherwise handled so that breakage occurs after it is sized on the main screens. This applies particularly to domestic coal, which should reach the consumer in as attractive condition as possible.

degraded illite

Illite that has lost much of its potassium as the result of prolonged leaching.

degreasing

Removal of oil and grease films from metal surfaces before electroplating, galvanizing, or enameling.

degreasing machine

An electrically driven machine including high-pressure pump and special cleaning solution for removing grease and oil from underground mine machines as a prevention of mine fires.

degree of compaction

The degree of compaction of a soil sample.

degree of consolidation

The ratio, expressed as a percentage, of the amount of consolidation at a given time within a soil mass, to the total amount of consolidation obtainable under a given stress condition.

degree of liberation

In mineral dressing, the degree of liberation of a certain mineral or phase is the percentage of that mineral or phase occurring as free particles in relation to the total of that mineral occurring in the free and locked forms.

degree of locking

In mineral dressing, the degree of locking of a mineral is the percentage occurring in locked particles in relation to the total occurring in the free and locked forms.

degree of packing

Of an explosive, the loading weight per unit of nominal volume, which is always known. Its unit is kilogram per cubic decimeter. The degree of packing defined in this way is 6% greater than the density of the explosive in the drill hole.

degree of saturation

a. The percentage of the volume of water-filled voids to the total volume of voids in a soil.

b. Ratio of weights of water vapor in air at given conditions and at saturation, with temperature constant. Specific humidities are usually employed. Measured in percent.

degree of size reduction

Ratio of the surface areas or sizes of the broken or crushed material to those of the feed material.

degree of sorting

a. The measure for the spread of grain-size distribution.

b. A measure of the spread or range of variation of the particle-size distribution in a sediment. It is defined statistically as the extent to which the particles are dispersed on either side of the average; the wider the spread, the poorer the sorting. It may be expressed by sigma phi.

degrees Kelvin

Absolute temperature on the centigrade scale, or degrees C plus 273.16.

degrees Rankine

Absolute temperature on the Fahrenheit scale, or degrees F plus 459.6.

Dehottay process

A variation of the freezing method of shaft sinking, in which liquid carbon dioxide is pumped into the ground instead of brine. See also: Oetling freezing method.

dehrnite

A hydrous phosphate of calcium, sodium, and potassium; hexagonal; crystalline crusts and minute crystals; grayish- to greenish-white. The mineral from Dehrn, Nassau, Germany, is richer in sodium, conforming nearly to the formula 7CaO.Na (sub 2) O.2P (sub 2) O (sub 5) .H (sub 2) O , whereas the mineral found near Fairfield, UT is described as 14CaO.2(Na,K) (sub 2) O.4P (sub 2) O (sub 5) 3(H (sub 2) O,CO (sub 2) ) .

dehumidification

The process of removing moisture from mine air to increase its cooling capacity--an important factor in environmental health and comfort in deep mining. See also: dry kata cooling power; effective temperature.

dehydrate

a. To render free from water.

b. The process of driving water from a hydrated mineral, e.g., gypsum, CaSO (sub 4) .2H (sub 2) O , to anhydrite, CaSO (sub 4) .

dehydrated

Freed from water or lacking water.

dehydrated stone

One from which the normal water content has been evaporated, usually by natural processes.

dehydrator

A device or material that will remove water from a substance. See also: dryer.

de-ionization

Removal of ions from solution by chemical means. Syn: demineralization.

Deister table

Proprietary type of shaking table used in mineral processing.

delaflossite

A trigonal mineral, CuFeO (sub 2) ; in the oxidized zone of copper deposits.

delatorreite

Former name for todorokite.

delatynite

A variety of amber rich in carbon, low in succinic acid, and lacking sulfur, at Delatyn in the Carpathian Mountains.

delawarite

An aventurine feldspar from Delaware County, PA.; a pearly orthoclase. Syn: lennilite.

delay

A distinct pause of predetermined time between detonation or initiation pulses, to permit the firing of explosive charges separately.

delay action

In blasting, firing of a round of shots in planned sequence so that cut or relief holes are blown first. Delay-action electric detonators have largely replaced safety fuses for this purpose, successive shots being separated by milliseconds.

delay blasting

The practice of initiating individual explosive decks, boreholes, or rows of boreholes at predetermined time intervals using delay detonators, as compared to instantaneous blasting where all holes are fired essentially simultaneously.

delay detonator

An electric or nonelectric detonator used to introduce a predetermined time lapse between the application of a firing signal and detonation.

delayed filling

Filling in which the mined-out rooms are filled later, generally on a large scale and when the neighboring sections are already being mined.

delayed pillar extraction

A pillar method of working in which the coal pillars are not extracted until the whole workings have been driven to the boundary. It is sometimes adopted when a seam a short distance above is worked simultaneously. Delayed pillar working increases the difficulty of ventilation, and the amount of deadwork is increased because of the crushing of coal pillars.

delayed quench

One in which the material is not quenched immediately on coming from the solution heat-treat furnace. This allows precipitation to proceed to a point at which mechanical properties and corrosion resistance are lowered.

delay electric blasting cap

An electric blasting cap with a delay element between the priming and detonating composition to permit firing of explosive charges in sequence with but one application of the electric current. It detonates about 1 to 2 s after the electric current has passed through the bridge. It is made in two kinds, first and second delay, and is used in connection with regular, waterproof, or submarine electric blasting caps for blasting in tunnels, shafts, etc., where it is desirable to have charges fired in succession without the necessity of the blaster returning betweeen shots.

delay element

An explosive train component consisting of a primer, a delay column, and a relay transfer charge assembled in a single housing to provide a controlled time delay.

delay firing

The firing of several shots in sequence, at designed intervals of time, usually by means of delay detonators, detonating relays, or sequence switches.

delay interval

The nominal period between the firing of successive delay detonators in a series of shots.

delay period

A designation given to a delay detonator to show its relative or absolute delay time in a given series.

delay rental

A payment, commonly made annually on a per acre basis, to validate a lease in lieu of drilling.

delay series

A series or sequence of delay detonators designed to satisfy specific blasting requirements. There are basically two types; millisecond (MS) and long period (LP).

delay tag

A tag, band, or marker on a delay detonator that denotes the delay series, delay period and/or delay time of the detonator. They are often color coded for convenience.

delay time

In seismic refraction work, the additional time required to traverse any raypath over the time that would be required to traverse the horizontal component at the highest velocity encountered on the raypath, as it refers to either the source or receiver end of the trajectory. Syn: intercept time.

delessite

A magnesian variety of chamosite.

delfman

Eng. A miner or worker in a stone quarry.

delhayelite

An orthorhombic mineral, (Na,K) (sub 10) Ca (sub 5) Al (sub 6) Si (sub 32) O (sub 80) (Cl (sub 2) ,F (sub 2) ,SO (sub 4) ) (sub 3) .18H (sub 2) O ; forms in laths in a melilite nephelinite lava at Mt. Shaheru, Kivu Province, Congo.

deliquescent

Capable of becoming liquid by the absorption of moisture from the air; e.g., calcium chloride crystals.

delivery column

See: rising main.

delivery date

The date on which a metal has to be delivered to fulfill the contract terms. Also called prompt date.

delivery drift

A drift or adit connected to a shaft from a point on the surface at a lower level than the shaft top and used as an outlet into which mine pumps discharge, so reducing the height through which the water must be lifted. Syn: jackhead.

delivery gate

Eng. A road into which a face conveyor delivers the coal.

delivery table

a. A conveyor that transports material from the discharge of a machine.

b. A table onto which a chute discharges.

dellenite

a. An extrusive rock between rhyolite and dacite in composition, and, broadly, the extrusive equivalent of granodiorite.

b. See: plagioclase rhyolite. c. A rhyodacite from Dellen Lake, Sweden.

dells

See: dalles.

delorenzite

See: tanteuxenite.

delphs

York. The working places in ironstone quarries.

Delprat method

See: overhand stoping.

delrioite

A monoclinic mineral, CaSrV (sub 2) O (sub 6) (OH) (sub 2) .3H (sub 2) O ; pale yellow-green microcrystalline efflorescence on sandstone occurring in Montrose County, CO.

delta iron

The polymorphic form of iron stable between 1,403 degrees F (762 degrees C) and the melting point (about 1,532 degrees F or 833 degrees C). The space lattice is the same as that of alpha iron and different from that of gamma iron.

deltaite

A mixture of crandallite and hydroxylapatite

deluge water system

A method of fire control in which water is sprayed or sprinkled in sufficient volume to overwhelm the fire and put it out.

Demag cappel

A rope cappel used in Koepe winding, particularly in Germany. The rope is led along the side of the eye and secured by a hinged retaining arm lined with rubber, and then turned around the eye and held in position by pressure exerted by knee-action links.

Demag drag-belt shuttle conveyor

Consists of a single length of belting, half the length of a double unit face, which is shuttled backward and forward along the face by means of low-type winches at each end of the face, interlocked and fitted with limit switches. The coal is plowed off the belt at the loader gate onto the gate conveyor.

demagnetize

To disperse, by means of a suitable magnetic field, solids in a dense medium that have flocculated magnetically.

demand respirator

An atmosphere-supplying respirator that admits respirable gas to the facepiece only when a negative pressure is created inside the facepiece by inhalation.

demantoid

A transparent, green variety of andradite, having a brilliant luster and used as a gem. Also called Uralian emerald.

demersal

See: benthonic.

demidovite

A phosphoriferous variety of chrysocolla from Tagilsk, Perm, Russia.

demineralization

a. Water softening by use of zeolites or resins to remove cations.

b. See: de-ionization.

demonstrated resources

A term for the sum of measured resources plus indicated resources.

dempy

A mine or part of a mine that is prone to outbursts and accumulations of noxious gases.

demulsification

Breakdown into separate phases of a relatively stable emulsion, by such means as flocculation with a surface-active agent or removal of an emulsifying agent.

demurrage

The detention of a vessel, railroad car, or other vehicle beyond an allotted time and for which a fee is usually charged.

dendriform

Resembling a tree, descriptive of some minerals. Syn: arborescent; dendritic.

dendrite

Any mineral forming branching moss-, fern-, or treelike patterns, e.g., some native silver and gold. Syn: dendrolite.

dendritic

Said of a mineral that has crystallized in a branching pattern. Syn: arborescent; dendriform.

dendritic and arborescent

A mineral in treelike or mosslike forms; e.g., manganese oxide.

dendritic drainage

The pattern of stream drainage in a region underlain by horizontally bedded rock, in which the valleys extend in many directions without systematic arrangement and have a dendritic (treelike) arrangement.

dendritic markings

a. Superficial dendrites on rock surfaces, joint faces, or other fractures, e.g., manganese oxyhydroxides on rock fracture surfaces.

b. Inclusion of a dendrite in another rock or mineral, e.g., chlorite in silica to form moss agate.

dendrolite

See: dendrite.

Denison core barrel

See: Denison sampler.

Denison sampler

A large-size, swivel-type double-tube core barrel designed for soil-testing work to obtain relatively undisturbed corelike samples of soft rock and/or soil formations. The inner tube is provided with a thin wall liner and a finger- or basket-type core lifter or core-retaining device. Also called Denison core barrel.

denningite

A tetragonal mineral, (Mn,Zn)Te (sub 2) O (sub 5) ; colorless to pale green; forms tetragonal plates and platy masses; at Sonora, Mexico.

dennisonite

A former name for davisonite. See: davisonite.

dense

a. Said of a fine-grained, aphanitic igneous rock whose particles average less than 0.05 to 0.1 mm in diameter, or whose texture is so fine that the individual particles cannot be recognized by the unaided eye.

b. Said of a rock whose constituent grains are crowded close together. The rock may be fine or coarse grained. c. Said of a rock or mineral possessing a relatively high specific gravity.

dense graded aggregate

Graded mineral aggregate which contains a sufficient number of very small particles to reduce the void spaces in the compacted aggregates to a minimum.

dense liquid

A homogeneous liquid or solution of specific gravity greater than that of water (e.g., zinc chloride and calcium chloride) that can be used in industry or in the laboratory to divide coal or other minerals into two fractions of different specific gravities.

dense-media separation

a. Heavy-media separation, or sink float. Separation of sinking heavy from light floating mineral particles in fluid of intermediate density. Abbreviation: DMS. See also: heavy-media separation.

b. Separation of relatively light (floats) and heavy (sinks) particles, by immersion in a bath of intermediate density. This is the dense or heavy media, a finely ground slurry of appropriate heavy material in water. Barite, magnetite ferrosilicon, and galena are in principal use.

dense medium

A fluid formed by the artificial suspension in water of heavy particles (e.g., magnetite, barite, and shale) that can be used in industry or in the laboratory to divide coal into fractions of different specific gravities.

dense-medium jigging

This method involves two essential features: (1) the circulation in the jig of a middling of approx. 3/16 in (4.8 mm) or smaller in size, with sp gr, 1.7 to 2.0--which fills the interstices of the jig bed and in effect converts the jig into a float-and-sink machine; and (2) the use of a suction stroke to hold the medium in the bed and prevent its washing over with the coal.

dense-medium process

A process for the washing of coal, in which the desired separation is effected in a dense medium.

dense-medium recovery

The collection, for reuse, of medium solids from dilute medium, usually understood to include the removal, in whole or in part, of contaminating fine coal and clay. Syn: medium-solids recovery.

dense-medium washer

A machine for cleaning coal and other materials that uses a dense fluid in which the coal floats and shale sinks. The fluid consists of water intimately mixed with sand (or finely ground magnetite or even shale) and agitated to maintain its consistency. The fluid has an effective specific gravity of 1.3 to 1.9. In general, coal from about 8 in (20.3 cm) down to 1 in (2.54 cm) is washed by dense medium, below 1 in by Baum washer, and below 0.75 mm (where cleaning is necessary) by froth flotation. Magnetite as the dense medium solid is preferred as it can be easily recovered by magnetic separators and also the upper limit of the specific gravity is higher (up to 2.0). See also: coal-preparation plant; washery.

dense noncrystalline tonstein

This type of tonstein consists almost entirely of fine-grained kaolin groundmass, showing weak aggregate polarization, containing isolated corroded crystals of kaolinite. Such bands are commonly more than 100 mm thick and light in color.

densimeter

An apparatus used to determine the relative density, or specific gravity, of a dense media.

densiscope

An apparatus to obtain the specific gravity of pearls as an indication, but not proof, of genuineness (cultured pearls tend to be denser).

densitometer

An instrument for the measurement of the density of an image produced by light, X-rays, gamma rays, etc., on a photographic plate; used in some dust-sampling instruments.

density

a. The mass of a substance per unit volume.

b. The quality or state of being dense; closeness of texture or consistency. c. The distribution of a quantity (as mass, electricity, or energy) per unit usually of space (as area, length, or volume). d. The ratio of the mass of any volume of a substance to the mass of an equal volume of a standard substance; water is used as the standard substance. e. Having the quality of being dense, hard, or compact. f. Weight of a substance in grams per cubic centimeter (at specified temperature when close accuracy is needed). For liquids and solids, it equals specific gravity. Density fluids are heavy liquids used in float-sink tests. Of a particle, the true density is its mass (m) divided by volume (v) excluding pores; its apparent density is its mass divided by volume (m/v) including open but excluding closed pores. Of a mass of particles (powder), the apparent density is mass divided by volume (m/v); the bulk density mass divided by volume (m/v) under stated freely poured conditions; and the tap density mass divided by volume (m/v) after vibrating or tapping under stated conditions. See also: apparent density; bulk density. g. Mass per unit volume. CF: specific gravity. h. Although density is defined as mass per unit volume, the term is frequently used in place of unit weight in the field of soil mechanics. See also: unit weight.

density contrast

The difference in density of a valuable mineral and the host rock.

density current

A current caused by differences in densities, for example, an excess of evaporation, cooling, or dilution in a restricted basin or an open sea.

density logger

An instrument for direct measurement of formation densities in boreholes. This tool furnishes a log of backscattered gamma radiation, which is a simple function of formation density.

density of dust cloud

The number of ounces of coal dust per cubic foot (or grams per cubic meter) of space, suspended in the air or gases in a specified zone.

density of gases

The vapor density of a gas, or its density relative to hydrogen, is the number of times a volume of the gas is heavier than the same volume of hydrogen, the volume of both gases being at the same temperature and pressure.

density of seams

a. An indication of the spacing of seams in the strata; the seam density is said to be high if the seams are close together, or low if they are widely separated.

b. The ratio of the sum of the thickness of a number of adjacent seams to the thickness of an arbitrarily chosen sequence of strata.

density ratio

In powder metallurgy, the ratio of the determined density of a compact to the absolute density of metal of the same composition, usually expressed as a percentage.

dental excavation

A controlled blasting technique used to minimize damage, in which the blasting of small, specially designed rounds over partial faces is used in extremely sensitive situations.

dental work

The act or process of filling cracks, crevices, or caverns encountered in drilling a borehole with cement or grout; also, the cracks, etc., so filled.

denudation

The sum of the processes that result in the wearing down of the surface of the Earth, including wear by running water, solution, and wind action.

Denver cell

A flotation cell of the subaeration type. Design modifications include receded-disk, conical-disk, and multibladed impellers, low-pressure air attachments, and special froth withdrawal arrangements.

Denver jig

Pulsion-suction diaphragm jig for fine material, in which makeup (hydraulic) water is admitted through a rotary valve adjustable as to the portion of jigging cycle over which controlled addition is made. Used in coal preparation for the removal of pyritic sulfur from thickener underflow material prior to its treatment by froth flotation. See also: jig.

Denver mud

See: bentonite.