Appendix:Dictionary of Mining, Mineral, and Related Terms/H/4

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a. Sometimes used as a prefix ("hyalo-") to names of volcanic rocks with a glassy texture, e.g., hyalobasalt.

b. Said of a mineral that is amorphous.


A variety of globular or botryoidal opal that shows greenish-yellow fluorescence under ultraviolet light and can be mistaken for uranium-bearing minerals such as autunite. Syn: glass opal; water opal.


A prefix meaning glassy.


Said of the texture of a porphyritic igneous rock in which crystals and glassy groundmass are equal or nearly equal in volumetric proportions, the ratio of phenocrysts to groundmass being between 5:3 and 3:5. Syn: semicrystalline; hemicrystalline.


A monoclinic or triclinic mineral, 4[(K,Ba)Al(Si,Al) (sub 3) O (sub 8) ] ; feldspar group, intermediate in the series orthoclase-celsian; prismatic cleavage; in manganese ore deposits, or veins and pegmatites.


Said of the texture of an igneous rock in which the mesostasis is glassy and makes up a proportion of the rock intermediate in texture between hyalophilitic and hyalocrystalline. CF: intersertal.

Hybinette process

A process used for refining of crude nickel anodes. These are placed in reinforced concrete tanks lined with asphalt. The nickel anodes are dissolved electrochemically and the impurities, such as copper and iron, pass into solution. The cathodes are surrounded by bags of closely woven canvas duck, fastened on wooden frames, and pure nickel electrolyte is passed continuously into them to maintain a higher solution level inside the cathode compartment than outside. By this means, the pure solution flows through the pores of the bags, thus preventing the ions of copper, etc., in the solution in the anode compartment from migrating into the cathode compartment, depositing on the cathode, and preventing the refining process from taking place. The electrolyte in the anode compartments is drawn off continuously and is purified in the copper cementation and iron precipitation departments before being returned to the cathode compartments of the nickel deposition tanks.


a. Pertaining to a rock whose chemical composition is the result of assimilation.

b. A rock whose composition is the result of assimilation. See also: hybridization.


The process whereby rocks of different composition from that of the parent magma are formed, by assimilation. See also: hybrid; assimilation; contamination.


The crystallization or precipitation of salts from normal aqueous solutions; the formation of an evaporite.


Derived from or modified by substances in a liquid condition; said of the genesis of ores and other minerals; opposite of pneumatogenic. CF: hydatopneumatogenic.


Said of a rock or mineral deposit formed by both aqueous and gaseous agents. CF: hydatogenic; pneumatogenic.

hydrabrake retarder

A mine car retarder, based on the principle of the dashpot, consists of individual braking units that can be fastened to the rails at spacings according to need over any desired distance. The unit offers no resistance to motion at very low car speeds, but as the speed increases, the braking force exerted upon it increases accordingly, following the usual oil dashpot characteristic. See also: dashpot.


See: gibbsite.


a. A compound or complex ion formed by the union of water with some other substance and represented as actually containing water.

b. A hydroxide, such as calcium hydrate (hydrated lime).

hydrated lime

A dry powder, Ca(OH) (sub 2) , obtained by hydrating quicklime.


a. The chemical combination of water with another substance.

b. The process of adding water, or the elements of water (oxygen and hydrogen combined in the hydroxyl radical), to any substance.


a. Conveyed, operated, effected, or moved by means of water or other fluids, such as a hydraulic dredge, using a centrifugal pump to draw sediments from a river channel.

b. Pertaining to a fluid in motion, or to movement or action caused by water. c. Hardening or setting under water; e.g., hydraulic lime or hydraulic cement.

hydraulic action

The mechanical loosening and removal of weakly resistant material solely by the pressure and hydraulic force of flowing water, as by a stream surging into rock cracks or impinging against the bank on the outside of a bend, or by a jet of water impacting a gravel bank.

hydraulic blasting

Fracture using a hydraulic cartridge, a ram-operated device used to split coal.

hydraulic cartridge

a. A device used in mining to split coal, rock, etc., having 8 to 12 small hydraulic rams in the sides of a steel cylinder.

b. See: coal burster.

hydraulic cement

A cement that can set and harden under water.

hydraulic cementing

A borehole-cementing operation using a downhole cement injector.

hydraulic chock

A steel face support structure consisting of from one to four hydraulic legs or uprights. The four-leg chock is mounted in a strong fabricated steel frame with a large head and base plate. It is controlled by a central valve system that operates either on the four legs simultaneously or on the front and rear pairs separately. See also: chock; yielding prop; self-advancing supports.

hydraulic chuck

A diamond-drill rod chuck having jaws with clamping and unclamping movements actuated hydraulically instead of by hand-turned setscrews.

hydraulic circulating system

A method used to drill a borehole wherein water or a mud-laden liquid is circulated through the drill string during drilling. See also: diamond drill.

hydraulic classifier

Tank into which ore pulp is fed steadily and subjected to the sorting effect of a stream of hydraulic water that rises at controlled rate. Heavier or coarser equal settling particles gravitate down and away via a bottom discharge, while lighter ones are carried up and out. Syn: hydrosizer. See also: elutriator.

hydraulic conveying

Use of flowing water or slow settling fluids based on water mixed with suitable heavy minerals to convey rock, coal, etc., in pipes.

hydraulic conveyor

A type of conveyor in which water jets form the conveying medium for bulk materials through pipes or troughs.

hydraulic cylinder

As applied to a diamond drill, a syn. for feed cylinder.

hydraulic discharge

The direct discharge of ground water from the zone of saturation, as via springs, wells, or infiltration ditches or tunnels.

hydraulic dredge

a. A dredge consisting of a hull on which is mounted a suction pipe and support, a pump with motors and controls, and a discharge line. Commonly used in dredging canals and in providing fill for the creation of land in near-shore or low-lying areas and in sand and gravel dredging operations.

b. A floating pump that sucks up a mixture of water and soil, and usually discharges it on land through pipes.

hydraulic dredger

A suction dredger.

hydraulic drill

A hand-held or machine-mounted rotary drill for boring shot-firing holes in coal or rock and operated by hydraulic fluid. The drill outfit includes a skid-mounted powerpack comprising a 5-hp (3.73-kW) flameproof electric motor, pump, and tank. The coal drill weighs about 32 lb (14.5 kg).

hydraulic elevator

An arrangement for lifting gravel and sand up to the drainage level. A jet of water is used to create a powerful suction in a hopper, and the water and gravel are carried up a pipeline and then run down the sluice boxes. This appliance was widely used in various goldfields toward the end of the 19th century.

hydraulic excavation

Excavation by means of a high-pressure jet of water, the resulting waterborne excavated material being conducted through flumes to the desired dumping point.

hydraulic extraction

A term that has been given to the processes of excavating and transporting coal or other material by water energy. Also called hydroextraction or hydraulic mining. See also: hydromechanization.

hydraulic feed

A method of imparting longitudinal movement to the drill rods on a diamond or other rotary-type drill by a hydraulic mechanism instead of mechanically by gearing.

hydraulic fill

Waste material transported underground and flushed into place by use of water. Syn: mine fill. See also: fill.

hydraulic-fill dam

A dam composed of earth, sand, gravel, etc., sluiced into place; generally the fines are washed toward the center for greater imperviousness.

hydraulic filling

Washing waste material, such as mill tailings and ground waste rock, into stopes with water to prevent failure of rock walls and subsidence. Problems involved in its use are stope preparation, choice and mixing of material, its particle size distribution, wear on pipe, and removal of water that transports the material into the mine. Compressed air may be used to force the filling through pipes.

hydraulic fluid

A fluid supplied for use in hydraulic systems. Low viscosity, low rate of change of viscosity with temperature, and low pour point are desirable characteristics. Hydraulic fluids may be of petroleum or nonpetroleum origin.

hydraulic fluid coupling

A hydraulic fluid coupling transmits power from the driving member to the driven member through oil. A rotating impeller attached to the drive shaft throws oil directly against a turbine converter, which always delivers the same torque as the engine or motor produces. Fluid couplings are particularly advantageous in starting heavy loads since the motor or engine is permitted to run at high efficient speeds while the coupling output shaft gradually accelerates the load to running speed.

hydraulic flume transport

The transport of coal, pulp, or mineral by the energy of flowing water in semicircular or rectangular channels. The gradient should not be less than 3 degrees . Coal movement in flumes commences at a water velocity of about 3 ft/s (0.9 m/s), but in practice a velocity of at least 6 ft/s (1.8 m/s) is arranged. See also: hydromechanization.

hydraulic flushing

See: hydraulic stowing.

hydraulic friction

The resistance to flow exerted on the perimeter or contact surface between a stream and its containing conduit, due to the roughness characteristic of the confining surface, which induces a loss of energy. Energy losses arising from excessive turbulence, impact at obstructions, curves, eddies, and pronounced channel changes are not ordinarily ascribed to hydraulic friction.

hydraulic giants

Used for working large placer deposits. Also called hydraulic monitors and water cannons.

hydraulic gradeline

In a closed conduit, a line joining the elevations to which water could stand in risers. In an open conduit, the hydraulic gradeline is the water surface.

hydraulic gradient

a. A line joining the points of highest elevation of water in a series of vertical, open pipes rising from a pipeline in which water flows under pressure.

b. Loss of hydraulic head per unit distance of flow. c. The slope of the hydraulic grade-line. The slope of the surface of water flowing in an open conduit.

hydraulic gravel-pump mining

Consists of the use of high-pressure water jets to disintegrate ore-bearing ground, together with gravel pumps to elevate the spoil to a treatment plant. Initial mining operations consist of the establishment of the mine hole or paddock. This is achieved by sinking or cutting downwards with monitors and removing the spoil by pumping, the pump being lowered as the hole deepens.

hydraulic hoisting

See: hydraulic transport.

hydraulic jack

A jack in which the lifting head is carried on a plunger working in a cylinder, to which oil or water is supplied under pressure from a small hand-operated pump. See also: hydrostatic press.

hydraulic jack operator

See: track-moving machine operator.

hydraulic jump

In fluid flow, a change in flow conditions accompanied by a stationary, abrupt turbulent rise in water level in the direction of flow. It is a type of stationary wave.


Excavating alluvial or other mineral deposits by means of high-pressure water jets. See also: hydraulic mining; hydromechanization; monitor. CF: ground sluicing.

hydraulic lime

Lime that is combined with silica, alumina, and iron oxide and will set and harden underwater.

hydraulic limestone

An impure limestone that contains silica and alumina (usually as clay) in varying proportions and that yields, upon calcining, a cement that will harden underwater. See also: cement rock. Syn: waterlime.

hydraulic load cell

A safety device developed by the U.S. Bureau of Mines for sensing pressure changes, thereby warning in advance of bumps. The cells are embedded in the walls and roofs of coal mines.

hydraulic loading

The flushing or slicing of coal or other material broken down by water jets along the floor and into flumes. Coal will flow back toward the flume if sufficient water is available and the gradient is not less than 6 degrees to 7 degrees in favor of the flow. Flexible low-pressure hoses (150 to 200 psi or 1.0 to 1.4 MPa) are sometimes used to assist in the flushing operations. See also: hydromechanization.

hydraulic machine

A borehole-drilling machine on which the bit-feeding mechanism is hydraulically actuated.

hydraulic main

A main (pipe) for collecting and condensing the volatile matter given off in carbonization of coal in the coking process.

hydraulic mean depth

The cross section of water flowing through a channel or pipe divided by the wetted perimeter of the conduit. Syn: hydraulic radius.

hydraulic mine filling

Filling a mine with material transported by water. CF: silting; slush. See: flush.

hydraulic miner

In metal mining, one who tends riffles, sluices, and does other work in connection with the hydraulic placer mining of gold. In this type of mining, gold bearing gravel, usually in a bank, is excavated by the erosive action of a high-pressure stream of water being directed at the bank through a nozzle. The gravel is then forced into sluices where the gold particles sink and are caught by riffles (cleats) along the sluice bottom.

hydraulic mining

a. Mining by washing sand and dirt away with water that leaves the desired mineral. See also: hydraulicking.

b. The process by which a bank of gold-bearing earth and rock is excavated by a jet of water, discharged through the converging nozzle of a pipe under great pressure, the earth or debris being carried away by the same water, through sluices, and discharged on lower levels into the natural streams and watercourses below; where the gravel or other material of the bank is cemented, or where the bank is composed of masses of pipe clay, it is shattered by blasting with powder. Also used for other ores, earth, anthracite culm, etc. Made unlawful and prohibited in certain river systems where it obstructs navigation and injures adjoining landowners. See also: placer mining. c. In underground hydraulic mining, the extraction of coal by high-velocity water jets, directed at the seam from a monitor or powerful jet, which can withstand high water pressures. The jets are also used to impel the broken coal along the floor to the point of collection. See also: hydromechanization; jet-assisted cutting.

hydraulic monitor

A device for directing a high-pressure jet of water in hydraulicking. It is essentially a swivel-mounted, counterweighted nozzle attached to a tripod or other type of stand and so designed that one person can easily control and direct the vertical and lateral movements of the nozzle. See also: giant; monitor.

hydraulic motor

A multicylinder reciprocating engine, generally of radial type, driven by water under pressure.

hydraulic permeability

The ability of a rock or soil to transmit water under pressure. It may vary according to direction.

hydraulic pipe transport

The conveyance of coal by means of water flowing in pipes. Coal may be pumped to the surface in shallow mines, but beyond 150 ft (46 m) or so of depth, there are technical difficulties. Solids handling pumps rarely deliver against heads exceeding about 200 ft (61 m). Two such pumps, placed in series, have been used in Trelewis Drift, Wales, to pump out slurry. See also: hydromechanization; transport.

hydraulic power

The use of pressure oil or soluble oil and water for operating face machines and steel supports. The fluid is supplied by rotary pumps driven by electricity located at points near the face. Hydraulic power has an advantage in that the space required is considerably less than that for conventional drives. See also: power pack.

hydraulic pressure

The total thrust, expressed in pounds or tons, that the hydraulic-feed mechanism on a drill can impose on a drill string; also, the pressure of the fluid within the hydraulic cylinders, generally expressed in pounds per square inch.

hydraulic profile

A vertical section of the potentiometric surface of an aquifer.

hydraulic prop

A prop consisting of two telescoping steel cylinders that are extended by hydraulic pressure that may be provided by a hand-operated pump built into the prop. The prop holds about half a gallon of mineral oil and is fitted with a yield valve that relieves the pressure when the load exceeds that for which the prop is set. A hydraulic prop enables quicker setting and uniform initial loading, and it can be withdrawn from a remote, safe position. The hydraulic prop was first used in a British coal mine in 1947. See also: steel prop.

hydraulic prospecting

The use of water to clear away superficial deposits and debris to expose outcrops, for the purpose of exploring for mineral deposits. Syn: hushing.

hydraulic radius

In a stream, the ratio of the area of its cross section to its wetted perimeter. Symbol: R. Syn: hydraulic mean depth.

hydraulic ram

a. A pump that forces running water to a higher level by utilizing the kinetic energy of flow, only a small portion of the water being so lifted by the velocity head of a much larger portion when the latter is suddenly checked by the closing of a valve. Also called ram.

b. A device for lifting water by the water hammer produced by checking the flow periodically. c. The plunger of a hydraulic press. d. A device whereby the pressure head produced when a moving column of water is brought to rest is caused to deliver some of the water under pressure.

hydraulic rotary drilling

Method of drilling that uses rotating bits lubricated by a stream of mud.


A branch of science that deals with practical applications, such as the transmission of energy or the effects of flow of water or other liquid in motion.

hydraulic set

The set obtained by the addition of water to hydraulic setting materials.

hydraulic sluicing

The process of moving materials by water; colloquially, hydraulicking.

hydraulic stowing

The filling of the waste in mines by waterborne material by pipeline. See also: pneumatic stowing. Syn: hydraulic flushing.

hydraulic stowing pipe

A steel or iron pipe used for transporting the material in hydraulic stowing. Ordinary pipes wear very rapidly owing to the chippings in the water; therefore, they are lined with abrasion-resistant material. This lining gives a very much longer life to the pipe.

hydraulic stripping

The excavation and removal of overburden by hydraulicking.

hydraulic transport

Movement of ore by water flowing through pipelines. Includes hydraulic hoisting. See also: pipeline transport.

hydraulic underreamer

An underreamer with cutting lugs that can be expanded or retracted by a hydraulically actuated device. See also: underreamer.

hydraulic valve

A valve for regulating the distribution of water in the cylinders of hydraulic elevators, cranes, etc.

Hydrik process

A commercial process for the production of hydrogen by reaction of caustic soda on aluminum.


Denotes a very common microlithotype in Japanese Tertiary coal. It consists of the macerals vitrinite, degradinite, and exinite. The dull bands of many Japanese Tertiary humic coals consist largely of hydrite and generally occurs alternating with vitrite as microfine bands, one or the other predominating.


An instrument for determining the depth of sea water by its pressure.


A monoclinic mineral, 1:1 interstratified biotite and vermiculite; in clay.


Any organic compound, gaseous, liquid, or solid, consisting solely of carbon and hydrogen. They are divided into groups of which those of special interest to geologists are the paraffin, cycloparaffin, olefin, and aromatic groups. Crude oil is essentially a complex mixture of hydrocarbons.

hydrocarbon anomaly

Very weak oil or gas seeps, so weak that the deposition of material at the surface cannot be recognized without chemical analysis.


A basic carbonate of lead, Pb (sub 3) (CO (sub 3) ) (sub 2) (OH) (sub 2) . It occurs as a secondary mineral found associated with leadhillite, matlockite, cerussite, mendipite, and paralaurionite.

hydrochemical anomaly

Anomalous patterns of elements contained in ground or surface water. See: anomaly.

hydrochemical prospecting

See: hydrogeochemical prospecting.

hydrocyanic acid

Unstable; volatile; colorless; extremely poisonous; gas or liquid; HCN; soluble in water, in alcohol, and in ether; only slightly dissociated with water; and an odor resembling that of bitter almonds. Formed by decomposing metallic cyanides with hydrochloric acid. Syn: hydrogen cyanide; prussic acid.


A cyclone separator in which a spray of water is used.

hydrodynamic computer codes

Computer codes or models that compute the properties or predicted behavior of explosives or materials subjected to supersonic (dynamic) forces.


The aspect of hydromechanics that deals with forces that produce motion. CF: hydrostatics.

hydrodynamic wave

An obsolete term for a type of surface wave that is similar to a Rayleigh wave but has an opposite particle motion. Syn: H wave.


An instrument for determining the velocity of a fluid in motion by its pressure.


See: hydraulic extraction.


See: centrifuge.


See: chalcophanite.


A member of the garnet group having SiO (sub 4) partly replaced by (OH) (sub 4) . CF: hydrogrossular; garnetoid.

hydrogenation of coal

See: coal liquefaction.

hydrogen cyanide

See: hydrocyanic acid.

hydrogen embrittlement

A condition of low ductility in metals resulting from the absorption of hydrogen.

hydrogen ion

The stripped (naked) proton of hydrogen, H+, or the proton combined with one or more molecules of water, as H (sub 3) O (super +) or H(H (sub 2) O) (super +) . The latter is sometimes called oxonium, hydroxonium, or hydronium ion. H+ is usually spoken of as the proton. H-ion concentration is the pH value.


a. Said of coals high in moisture, such as brown coals.

b. Said of coals high in volatiles, such as sapropelic coals.

hydrogen sulfide

Colorless; flammable; gas; H (sub 2) S . It is readily decomposed. Reacts with bases forming sulfides and with some metals to produce metal sulfides and to liberate hydrogen. Poisonous. Syn: hydrosulfuric acid.

hydrogeochemical prospecting

Prospecting guided by the composition of ground or surface water. Syn: hydrochemical prospecting.


A graph showing stage, flow, velocity, or other characteristics of water with respect to time. A stream hydrograph commonly shows rate of flow; a ground-water hydrograph, water level or head.


a. The science that deals with the physical aspects of all waters on the Earth's surface, esp. the compilation of navigational charts of bodies of water.

b. The body of facts encompassed by hydrography.


A group name for the series of hydrogarnets encompassing the series hibschite, katoite, and grossular. Water content ranges from about 1.5% in hibschite to 13% in katoite; grossular is anhydrous. Syn: hydrogarnet. CF: garnetoid; hydrogarnet.


A mineral, Fe (sub 2) O (sub 3) .nH (sub 2) O , probably a mixture of the two minerals haematite and goethite, the former being in excess. It is fibrous and red in mass, with an orange tint when powdered. Also called turgite. See also: turgite.

hydrologic cycle

The constant circulation of water from the sea, through the atmosphere, to the land, and its eventual return to the atmosphere by way of transpiration and evaporation from the sea and the land surfaces. Syn: water cycle.


a. The science that deals with global water (both liquid and solid), its properties, circulation, and distribution, on and under the Earth's surface and in the atmosphere, from the moment of its precipitation until it is returned to the atmosphere through evapotranspiration or is discharged into the ocean. In recent years, the scope of hydrology has been expanded to include environmental and economic aspects.

b. The sum of the factors studied in hydrology; the hydrology of an area or district.


a. The formation of an acid and a base from a salt by interaction with water, caused by the ionic dissociation of water.

b. The decomposition of organic compounds by interaction with water; either cold, or on heating alone, or in the presence of acids or alkalies.


A monoclinic mineral, Mg (sub 5) (CO (sub 3) ) (sub 4) (OH) (sub 2) .4H (sub 2) O; pseudo-orthorhombic; in low-temperature veins in serpentinite.


The mechanics of fluids, including hydrostatics, hydrodynamics, hydrokinetics, and pneumatics.


A term applied to hydraulic methods of excavating and transporting coal and other products underground. See also: hydraulic extraction; hydraulic flume transport; hydraulic loading; hydraulic mining; hydraulic pipe transport; hydraulicking.


The treatment of ores, concentrates, and other metal-bearing materials by wet processes, usually involving the solution of some component, and its subsequent recovery from the solution. Syn: wet metallurgy.


Alteration of rock by material that is added, removed, or exchanged by water solutions, without the influence of high temperature and pressure. Syn: hydrometasomation; hydrometasomatism. CF: pyrometamorphism.


See: hydrometamorphism.


See: hydrometamorphism.


An instrument used for determining the density or specific gravity of fluids, such as drilling mud or oil, by the principle of buoyancy. See also: gravimeter; Marsh funnel; specific-gravity hydrometer.

hydrometer method

The method employed for the determination of the apparent specific gravity of coal and coke.


An instrument for determining and recording the quantity of water discharged from a pipe, orifice, etc., in a given time.


a. See: illite.

b. A general term for brammallite, hydrobiotite, and illite.

hydromorphic anomaly

An anomaly where the dynamic agents are aqueous solutions, which brought the elements to the site of deposition.


See: illite.

hydronium jarosite

A trigonal mineral, (H (sub 3) O)Fe (sub 3) (SO (sub 4) ) (sub 2) (OH) (sub 6) ; alunite group.


a. Of, relating to, having, or denoting a strong affinity for water.

b. Applied to such easily dispersed colloidal clay minerals as montmorillonite that swell in water as the result of water attraction and hydration and that are not easily coagulated. c. Substance attracted to a water phase rather than to air in an airwater interphase. A group tending to bind water is hydrophilic (opposite of hydrophobic). The hydroxyl (OH) groups in hydroxides are typical, and their hydrophilic solutions in water are hydrosols. See also: lyophilic. q/ 6[? ._? � � � � � DICTIONARY TERMS:hydrophobic a. Lacking a strong affinity for water. a. Lacking a strong affinity for water. Opposite of hydrophilic. b. Applied to water-repelling substances and surfaces and to easily coagulated colloids.


A pressure-sensitive detector that responds to sound transmitted through water. It is used in marine seismic surveying, or as a seismometer in a well. Syn: pressure detector.


A sensitive instrument used in water transparency and light absorption measurements at sea. The instrument, which contains its own light source, can measure fine graduations of transparency of an individual water mass.


An instrument for detecting moisture, esp. in the air.


Essentially, a shallow tank, usually cylindrical, which is kept agitated by hydraulic water and/or stirring devices. Pulp fed to the tank is separately discharged as a free-settling fraction containing the coarser and heavier particles and an overflowing fraction containing the finer, lighter material.


See: hydraulic classifier.


The waters of the Earth, as distinguished from the rocks (lithosphere), living things (biosphere), and the air (atmosphere). Includes the waters of the ocean; rivers, lakes, and other bodies of surface water in liquid form on the continents; snow, ice, and glaciers; and liquid water, ice, and water vapor in both the unsaturated and saturated zones below the land surface. Included by some, but excluded by others, is water in the atmosphere, which includes water vapor, clouds, and all forms of precipitation while still in the atmosphere.


A contrivance or apparatus to prevent the explosion of steam boilers.


Relating to the pressure or equilibrium of fluids.

hydrostatic balance

A balance for weighing a substance in water to ascertain its specific gravity.

hydrostatic head

The height of a vertical column of water whose weight, if of unit cross section, is equal to the hydrostatic pressure at a given point; static head as applied to water. See also: static head.

hydrostatic joint

Used in large water mains, in which sheet lead is forced tightly into the bell of a pipe by means of the hydrostatic pressure of a liquid.

hydrostatic press

A large ram, the surface of which is acted on by liquid in contact with a small ram. See also: hydraulic jack.

hydrostatic pressure

a. Stress that is uniform in all directions, e.g., beneath a homogeneous fluid, and causes dilation rather than distortion in isotropic materials.

b. The pressure exerted by the water at any given point in a body of water at rest. The hydrostatic pressure of ground water is generally due to the weight of water at higher levels in the zone of saturation.

hydrostatic roller conveyor

A section of roller conveyor having rolls suitably weighted with liquid to control the velocity of the moving objects. See also: roller conveyor.


A branch of physics that deals with the characteristics of fluids at rest and esp. with the pressure in a fluid or exerted by a fluid on an immersed body. CF: hydrodynamics.

hydrostatic stress

A state of stress in which the normal stresses acting on any plane are equal and where shearing stresses do not exist in the material.

hydrostatic test

On a boiler, the closing of all openings and pumping water into the boiler at a pressure (such as 50%) greater than the normal operating pressure. The purpose is to locate leaks or prove that there are no leaks.

hydrosulfuric acid

See: hydrogen sulfide.


The mineral group desautelsite, hydrotalcite, pryoaurite, reevesite, stichtite, and takovite.


An electrically operated apparatus showing at a distance the exact level of water, as in a reservoir; an electric high- and low-water indicator.


A coal washer of the classifier type whose agitator or rotator consists of hollow arms radiating from a central distributing manifold or center head. There may be four or more of these radiating arms, each with one or more downwardly inclined nozzles. When water is discharged from these nozzles, the impulse has the effect of rotating the agitator in a manner similar to a lawn sprinkler. This agitator is suspended in a cylindrical tank and water is pumped through it under pressure, thereby creating a controlled upward current uniform over the entire area of the tank.


Of or pertaining to hot water, to the action of hot water, or to the products of this action, such as a mineral deposit precipitated from a hot aqueous solution, with or without demonstrable association with igneous processes; also, said of the solution itself. Hydrothermal is generally used for any hot water but has been restricted by some to water of magmatic origin.

hydrothermal alteration

Alteration of rocks or minerals by the reaction of hydrothermal water with preexisting solid phases.

hydrothermal deposit

A mineral deposit that originated from hot, ascending aqueous solutions derived from a magma. CF: hypothermal deposit.

hydrothermal solution

A hot-water solution originating within the Earth and carrying dissolved mineral substances. Syn: ore-bearing fluid; ore-forming fluid.

hydrothermal stage

That stage in the cooling of a magma during which the residual fluid is strongly enriched in water and other volatiles. The exact limits of the stage are variously defined by different authors, in terms of phase assemblage, temperature, composition, and/or vapor pressure; most definitions consider it as the last stage of igneous activity, coming at a later time, and hence at a lower temperature, than the pegmatitic stage.

hydrothermal synthesis

Mineral synthesis in the presence of water at elevated temperatures.


a. Containing water; watery; specif., hydrated.

b. Minerals that contain water chemically combined.

hydrous salts

Salts containing water of crystallization.


A permitted device, used in some English coal mines, that resembles Cardox in that a steel cylinder with a thin shearing disk is used. However, the charge is not liquid carbon dioxide but rather a powder composed chiefly of ammonium chloride and sodium nitrate. It is proportioned to give water, nitrogen, and salt as the products of combustion. On being ignited, this powder is gasified and shears the steel disk, with the gas escaping into the hole.

Hydrox steel tube

An alternative to explosives for breaking down coal in safety lamp mines. The gasification of the Hydrox charge generates sufficient pressure within the shothole to break down the coal. The original plastic disc attached to the charge has been replaced by a metal disc separately seated. The gaseous products from the Hydrox charge are mainly carbon dioxide, nitrogen, and water vapor. The tubes can be recharged underground. The method gives a high yield of +2 in (5.1 cm) in size of coal.


See: phenol.


OH; the characteristic radical of bases, consisting of one atom of hydrogen and one atom of oxygen. The valence of this radical or anion is -1.


A hexagonal mineral, Ca (sub 5) (PO (sub 4) ) (sub 3) (OH) ; apatite group; an uncommon apatite in which hydroxyl predominates over fluorine and chlorine. Formerly spelled hydroxyapatite.


A monoclinic mineral, 2[Zn (sub 5) (CO (sub 3) ) (sub 2) (OH) (sub 6) ] ; forms massive, fibrous, earthy, or compact encrustations with blue luminescence; a secondary mineral in weathered zones of zinc deposits commonly associated with smithsonite or sphalerite; a source of zinc. Syn: zinc bloom.


See: rain gage.


Any of several instruments for measuring the humidity of the atmosphere. See also: psychrometer.


Measurement of atmospheric humidity.

hygroscopic water content

The water content of an air-dried soil.


A device sensitive to humidity changes and arranged to actuate other equipments when a predetermined humidity is attained. Syn: humidostat.


Pertaining to an igneous intrusion, or to the rock of that intrusion, whose depth is intermediate between that of abyssal or plutonic and the surface. This distinction is not considered relevant by some petrologists. CF: abyssal; plutonic. Syn: subvolcanic.

hypabyssal rock

An igneous rock that has risen from the depths as magma but solidified mainly as such minor intrusions as dikes and sills.


A prefix from the Greek meaning over, above, or abnormally great.


Any substance capable of lowering the melting ranges in end-stage magmatic fluids.


Said of igneous rocks that consist of 90% to 100% mafic minerals. CF: melanocratic; ultramafic.


A class of short-lived elementary nuclear particles with masses greater than that of the neutron.


An orthorhombic mineral series, 8[(Mg,Fe) (sub 2) Si (sub 2) O (sub 6) ] ; pyroxene group, intermediate between enstatite and ferrosilite; prismatic cleavage; a common rock-forming mineral in intermediate to mafic igneous rocks and high-grade metamorphosed iron formations of the Lake Superior type; abundant in host rocks of copper-nickel ores of Sudbury, ON, Canada, and of chromite deposits of the Bushveld complex, South Africa. See also: pyroxene.


Originally defined as a syn. of norite, but now commonly used to mean a rock composed entirely of hypersthene; an orthopyroxenite. Not recommended usage.


See: subhedral.

hypidiomorphic texture

A texture of igneous rocks in which the greater proportion of the crystallized minerals have subhedral forms.

hypnum peat

Peat composed mostly of disintegrated plants of hypnum, often associated with other mosses and with intermingled rootlets of sedges and other flowing plants. It is formed chiefly in areas where the ground is only slightly acid, neutral, or slightly alkaline; it is brownish or drab, light, spongy, and matted, and often laminated and porous.

hypobatholithic deposit

A mineral deposit found in a deeply eroded mass of intrusive rock with few roof pendants remaining.


See: focus.


Said of the texture of an igneous rock that has crystalline components in a glassy groundmass, the ratio of crystals to glass being between 7:1 and 5:3. Syn: merocrystalline.


See: hypogene.


See: hypogene.


a. Said of a geologic process, and of its resultant features, occurring within and below the crust of the Earth. CF: epigene; endogenetic. Syn: hypogenic; hypogeal; hypogeic.

b. Said of a mineral deposit formed by ascending solutions; also, said of those solutions and of that environment. CF: supergene; mesogene. c. A rarely used syn. of plutonic.

hypogene ore

Ore deposited from ascending hydrothermal solutions of magmatic origin.

hypogene rock

A rock that was formed deep within the Earth under the influence of heat and pressure.


See: hypogene.


Said of the texture of an igneous rock that has crystalline components in a glassy groundmass, with a ratio of crystals to glass between 3:5 and 1:7. CF: hypocrystalline.

hypothermal deposit

Said of a hydrothermal mineral deposit formed at high temperatures and pressures. CF: epithermal; hydrothermal deposit; leptothermal; mesothermal; telethermal; xenothermal.


A conception or proposition that is tentatively assumed, and then tested for validity by comparison with observed facts and by experimentation; e.g., the planetesimal hypothesis to explain the evolution of the planets. It is less firmly founded than a theory.

hypothetical resources

Undiscovered resources that are similar to known mineral bodies that may be reasonably expected to exist in the same producing district or region under analogous geologic conditions. If exploration confirms their existence and reveals enough information about their quality, grade, and quantity, they will be reclassified as identified resources.


An instrument for measuring the elevation above sea level by determining the atmospheric pressure through observing the boiling point of water.

hypsometric map

Any map showing relief by means of contours, hachures, shading, tinting, or any other convention.


The science of determining, by any method, elevations on the Earth's surface with reference to sea level; e.g., barometric hypsometry in which elevations are determined by means of mercurial or aneroid barometers.


a. A lag in the return of an elastically deformed body to its original shape after the load has been removed.

b. The property that a rock is said to exhibit when its magnetization is nonreversible. Syn: magnetic hysteresis. c. A phase lag of dielectric displacement behind electric-field intensity, due to energy dissipation in polarization processes.

hysteresis loop

Entire pattern of magnetization showing how a body with magnetic susceptibility can remain polarized after the disappearance of the original magnetizing force.

hysteretic repulsion

Separation by alternating current that depends on magnetic properties of coercive force and remanence.