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

head

a. Any road, level, or other passage driven in coal, etc., for the purpose of proving and working the mine.

b. The top portion of a seam in the coal face. c. The whole falling unit in a stamp battery, or merely the weight at the end of the stem. d. The top end of the boring rods above the surface. e. Core-barrel head. f. In gravity separation of a feed, the heads are the concentrates. Opposite of tail. g. Variously used as a syn. for core-barrel head; drill head; swivel head. h. The attitude or direction in a massive crystalline rock along which fracture is most difficult. It is normal to the grain and rift. i. The difference in air pressure producing ventilation. j. In mineral processing, the mill head, or grade of ore, accepted by the mill for treatment. Commonly used in the plural. k. The height of water above any point or plane of reference. Used also in various compounds, such as energy head, entrance head, friction head, static head, pressure head, lost head, etc. l. A unit of pressure intensity usually given in inches or feet (millimeters or meters) of a column of the fluid under consideration. Thus, 1 ft (or m) of water head is the pressure from a column of water 1 ft (or m) high. m. The upper bend of a fold or structural terrace. CF: foot. Syn: upper break. n. An advance main roadway driven in solid coal. o. Development openings in a coal seam. p. Total head (th). Also called head on pump. q. So. Staff. A shift or day's work by the stint in heading-out, or driving of dead work. r. To cut or otherwise form a narrow passage or head. s. A lift. t. As applied to rock, natural planes of cleavage at right angles to the grain and the rift of the rock. u. Rubble drift on the cliffs of southern England.

headache post

A timber set under the walking beam to prevent it from falling on members of the drilling crew when it is disconnected.

headblock

a. A stop at the head of a slope or shaft to stop cars from going down the shaft or slope.

b. A cap piece. c. A heavy obstruction placed end-on across the rail to prevent the passage of a runaway mine car. d. The crosstie that supports the toes of the switch. e. Commonly used as a syn. for crown block; sheave wheel.

headboard

a. A wedge of wood placed against the hanging wall, and against which one end of the stull is jammed.

b. A horizontal board in the roof of a heading, touching the earth above and supported by a headtree at each side.

headbox

A device for distributing a suspension of solids in water to a machine at a constant rate, or for retarding the rate of flow, as to a top-feed filter or for eliminating by overflow some of the finest particles.

head coal

Scot. Formerly, the stratum of a coal next to the roof. More usually now, the top portion of a coal seam when left unworked, either permanently or afterwards taken down; the top coal on a loaded wagon.

head end

a. Usually the ultimate delivery end of a conveyor.

b. That part of a mining belt conveyor that includes the head section, a power unit, and, if required, the connecting section and a belt takeup.

header

a. Pieces of plank--longer than a cap--extending over more of the roof and supported by two props, one at each end.

b. An entry-boring machine, called a road header, which bores the entire section of the entry in one operation. c. The person in charge of driving a heading. d. A rock that heads off or delays progress. e. A blasthole at or above the head. f. A masonry unit laid flat with its greatest dimension perpendicular to the face of the wall; generally used to tie two wythes of masonry together. g. A large pipe into which one set of boilers is connected by suitable nozzles or tees, or similar large pipes from which a number of smaller ones lead to consuming points. Headers are essentially branch pipes with many outlets, which are usually parallel.

head flat trimmer

In bituminous coal mining, a foreman who is in charge of workers picking impurities from coal as it is dumped into railroad cars at the mine surface.

headframe

a. The steel or timber frame at the top of a shaft, which carries the sheave or pulley for the hoisting rope and serves various other purposes. Also called gallows frame; hoist frame; head stocks.

b. The shaft frame, sheaves, hoisting arrangements, dumping gear, and connected works at the top of a shaft or pit. Also called headgear. c. Includes all the raised structure around the shaft that is used for loading and unloading cages. d. Can. Gallows over the shaft to which cable for hoisting is attached.

headgear

a. See: headframe.

b. That portion of the winding machinery attached to the headframe, or the headframe and its auxiliary machinery.

head grain

See: hard way.

headhouse

a. The house or building that encloses the headframe.

b. The structure on a hillside to control the lowering of coal to the tipple.

heading

a. A passage leading from the gangway, commonly at right angles in a coal mine.

b. A smaller excavation driven in advance of the full-size section; it may also be driven laterally, as a cross heading or side drift. A heading may be driven at the top or the bottom of the full-size face. c. The vein above a drift. d. An interior level or airway driven in a mine. e. A road in the solid strata but also in the seam; a road in solid coal. f. In a tunnel, a digging face and its work area; the end of a drift or gallery that is being advanced by the mining operation. g. A gangway, entry, or airway. h. The gravel bank above a sluice in a placer. i. A continuous passage between two rooms, breasts, or other working places. j. A collection of close joints. k. Sometimes applied to the preliminary drift or pioneer bench in tunnel driving.

heading-and-bench

A method of tunneling in hard rock. The heading is in the upper part of the section and is driven only a round or two in advance of the lower part or bench.

heading-and-bench mining

A stoping method used in thicker ore where it is customary first to take out a slice or heading 7 to 8 ft (2.1 to 2.4 m) high directly under the top of the ore and then to bench or stope down the ore between the bottom of the heading and the bottom of the ore or floor of the level. The heading is kept a short distance in advance of the bench or stope. Syn: heading-and-stope mining.

heading and stall

See: room-and-pillar.

heading-and-stope mining

See: heading-and-bench mining.

heading blast

A method of quarry blasting in which the explosive is confined in small tunnel chambers inside the quarry face. The charges are placed at suitable intervals according to the burden to be blasted. In large blasts, several tunnels and cross tunnels may be employed. See also: chamber. Syn: tunnel blast.

heading-overhand bench

The heading is the lower part of the section and is driven at least a round or two in advance of the upper part, which is taken out by overhand excavating. Syn: inverted heading and bench.

headings

a. Coarse gravel or drift overlying placer deposits.

b. The portion of a vein that is above a level. c. Highly jointed parts of granite. d. In ore beneficiation, the purest ore obtained by washing, as opposed to middlings and tailings. Also called concentrates. See also: heads.

heading seam

See: joint.

heading side

See: footwall.

heading wall

See: footwall.

headline

In dredging, the line that holds the dredge up to its digging front. This line is anchored well ahead of the dredge pond or paddock and attached to a winch on the dredge. Lateral movement is controlled by sidelines similarly led from winches to land anchorages, usually two on each side. See also: sideline.

head motion

Vibrator of shaking table that imparts reciprocating motion to the deck.

head-of-hollow fill

A fill structure consisting of any materials, other than a coal processing waste or organic material, placed in the uppermost reaches of a hollow where side slopes of the existing hollow measured at the steepest point are greater than 20 degrees , or the average slope of the profile of the hollow from the toe of the fill to the top of the fill is greater than 10 degrees . In fills with less than 250,000 yd (super 3) (191,000 m (super 3) ) of material, associated with steep slope mining, the top surface of the fill will be at the elevation of the coal seam. In all other head-of-hollow fills, the top surface is the fill, which when completed, is at approx. the same elevation as the adjacent ridge line, and no significant area of natural drainage occurs above the fill draining into the fill areas.

head piles

The top poling boards in a heading.

head pulley

a. The discharge pulley of the conveyor. It may be either an idler pulley or a drive pulley. A head pulley that is mounted on a boom is termed an extended head pulley; a head pulley that is separately mounted is termed a detached head pulley.

b. The crowned pulley or idler mounted at the extreme front end or delivery point of a belt conveyor. The belt, after passing around this pulley, begins its travel toward the tail end or foot section of the conveyor.

head-pulley-drive conveyor

A conveyor in which the belt is driven by the head pulley without a snub pulley.

head-pulley-snub-drive conveyor

A conveyor in which the belt is driven by the head pulley with a snub pulley.

headrace

Sluice aqueduct, leat, or launder that leads water to head of operation or to waterwheel. A forebay.

headroom

Height between the floor and the roof in a mine opening.

headrope

In any system of rope haulage, the rope that is used to pull the loaded transportation device toward the discharge point. In scraper loader work, the headrope pulls the loaded scoop from the face to the dumping point.

heads

a. In ore dressing, the feed to a concentrating system. CF: tails.

b. Low-grade material overlying an alluvial placer. c. In New York and Pennsylvania, a local term applied by bluestone quarrymen to the open joints that run north and south. d. See: headings. e. Scot. Large top coal on a loaded hutch. f. Aust. Small faults. g. Low-grade wash overlying the wash proper. h. Can. Material taken from ore in treatment plant and containing the valuable metallic constituents. Opposite of tails.

head section

A term used in both belt and chain conveyor work to designate that portion of the conveyor used for discharging the coal.

head shaft

The shaft mounted at the delivery end of a chain conveyor, on which is mounted a sprocket that drives the drag chain. The shaft, in turn, is driven by means of a drive chain from the speed reducer of the power unit through a sprocket mounted on the shaft end.

head sheave

Pulley in headgear of the winding shaft over which the hoisting rope runs. See also: winding sheave.

head side

N. Staff. The rise side of a heading driven on the strike.

headsticks

See: headgear; headframe.

headstocks

See: headframe.

headsword

Corn. Water discharged through the adit level.

head tank

Any tank or vessel in the water circuit that is used to control the delivery pressure of the water to the washing units.

headtree

a. The horizontal timber at each side of a rectangular heading that supports the headboard. See also: side trees.

b. The cap piece of a heading set.

head value

The assay value of the heads or mill feed.

headwall

a. Retaining wall at both ends of a culvert or similar structure.

b. A culvert sidewall; sometimes only the upstream wall.

headway

The second set of excavations in post-and-stall work. See also: crossheading.

headwork

a. Arkansas. The cutting and other work done at the face of an entry.

b. The headframe with the headgear.

heap

a. Scot. To load up a tub (car) or truck above the top of the sides.

b. The soil carried above the sides of a body or bucket. c. Newc. The refuse at the pit's mouth.

heap closure

See: heap decommissioning.

heap decommissioning

Legal closure of a heap leaching operation. Depends on individual State regulations, but includes requirements for physical stability and chemical effluent requirements for metals and pH. A monitoring period is included. Syn: heap closure.

heaped capacity

In scraper or truck loading, a term used to describe the volume of material the scraper will hold when the material is heaped. Frequently, sideboards are added to increase the heaped capacity. Heaped capacity will exceed struck capacity by approx. one-third, depending upon the heaping condition assumed. CF: struck capacity.

heap leaching

A process used for the recovery of copper, uranium, and precious metals from weathered low-grade ore. The crushed material is laid on a slightly sloping, impervious pad and uniformly leached by the percolation of the leach liquor trickling through the beds by gravity to ponds. The metals are recovered by conventional methods from the solution.

heap matte

Matte produced by heap roasting.

heap rinsing

Method used to remove soluble constituents remaining within a heap leach pile after the metals concentration decreases to levels below economic limits. Simple water rinsing, chemical, or biological techniques or combinations thereof may be employed.

heap roasting

of fuel.

heap sampling

Method of reducing a large sample of ore to yield a representative sample. A conical heap is made by shoveling the material accurately on to the apex so that it runs down equally all around. The heap can then be flattened somewhat by rubbing with a spade, and is shoveled into four equal heaps, the same amount being taken from the base of the cone each time the worker goes around. Of the four smaller heaps thus formed, two are discarded and two retained. These may now be crushed to improve the ease of thorough mixing, and are then formed into another cone in the same way as the first. The process is repeated, with periodic size reduction of the retained portions, until the required small sample has been produced.

heapstead

The buildings and surface works around a colliery shaft.

hearth

a. The bottom portion of certain furnaces, such as a blast furnace, air furnace, and reverberatory furnace, in which molten metal is collected or held.

b. The part of a furnace in which heat is developed for the purpose of melting glass. c. A plate or table upon which cylinder glass is flattened.

hearth and bosh brick

Fireclay brick for use in lining the hearth walls and bosh sections of a blast furnace.

hearth furnaces

Furnaces in which the charge rests on the hearth or kiln wall and is heated by hot gases passing over it. Even though hearth furnaces such as the multiple-hearth roasting furnace and rotary kilns operate on the same basis as reverberatory furnaces, they bear little resemblance to them.

hearthplate

A cast-iron plate serving as a sole for a refiner's furnace.

hearth roasting

A roasting process in which the ore or concentrate enters at the top of a multiple hearth roaster and drops from hearth to hearth in succession until it is discharged at the bottom. In the downward progress of the ore, the sulfide particles are roasted as they come in contact with the heated air.

heart joint

Scot. A particular form of attachment joint between the bucket rod and the foot rod of a pump.

heat

a. One operation in a furnace not operating continuously.

b. The energy a body possesses because of the motion of its molecules. c. Energy in transit from a higher temperature system to a lower temperature system. The process ends in thermal equilibrium. d. The material heated, melted, etc., at one time; as, the foundry runs three heats a day. e. Form of energy generated or transferred by combustion, chemical reaction, mechanical means, or passage of electricity, and measurable by its thermal effects.

heat balance

a. In furnaces, heat engines, etc., the distribution of the known input of energy (as heat); also, the method of determining, or the graphical or tabular record of, such distribution.

b. In fluidization roasting, the thermodynamic calculation used to control addition or removal of heat in order to maintain the desired temperature in the reacting vessel. c. Equilibrium that exists on the average between the radiation received by the Earth and its atmosphere from the Sun and that emitted by the Earth and its atmosphere. That the equilibrium does exist in the mean is demonstrated by the observed long-term constancy of the Earth's surface temperature. On the average, regions of the Earth nearer the equator than about 35 degrees latitude receive more energy from the Sun than they are able to radiate, whereas latitudes higher than 35 degrees receive less. The excess of heat is carried from low latitudes to higher latitudes by atmospheric and oceanic circulations and is reradiated.

heat capacity

That quantity of heat required to increase the temperature of a system by 1 degrees at constant pressure and volume. It is usually expressed in calories per degree Celsius. Syn: thermal capacity.

heat conductivity

See: thermal conductivity.

heated stone

A stone that has been artificially heated to the proper temperature with the intention of improving or completely altering its color. The induced color is permanent in varieties, such as hyacinth, burnt amethyst, etc.; less permanent in blue zircon. See also: fired stone. Syn: heat-treated stone; burnt stone. CF: stained stone.

heat energy

Energy in the form of heat.

heat engine

A mechanism (as an external-combustion or an internal-combustion engine) for converting heat energy into mechanical energy.

heater

In the coke products industry, one who regulates the temperature of heating flues and combustion of fuel gas used to heat coal in a byproduct coke oven.

heater drain pump

Self-regulating pumps capable of dealing with water at fairly high temperatures and pressures. They are used to return heater condensate to the feed line instead of to waste.

heat exchanger

Any device that transfers heat from one medium to another or to the environment.

heating back

A chamber back of a forge in which the air intended for the blast is heated.

heating medium

A fluid used for conveying heat from a heat source to heat-dissipating devices; includes air, water, and steam.

heatings

The heat generated before an actual mine fire occurs. Heatings, or incipient fires, are detected in mines by smell and by analysis of air samples. In mines liable to spontaneous combustion, trained officials and workers are employed to detect and deal with heatings and fires and they become expert in these duties.

heating surface

a. That surface in a steam boiler or similar apparatus from which heat passes to the liquid to be evaporated or heated; the fire surface.

b. Broadly, the area intended for transferring heat.

heating tendency

The ability of a coal to fire spontaneously. This phenomenon can occur whenever the heat generated from oxidation reactions in a coal exceeds the heat dissipated. This characteristic varies for different types of coals and even for coals of the same classification but of different origin.

heat of combustion

The heat of reaction resulting from the complete burning of a substance and expressed variously (as in calories per gram or per mole, or esp. for fuels in British thermal units per pound or per cubic foot).

heat of compression

As air passes down shafts and along inclined workings, it is compressed. Heat is always generated when air is compressed, and although the reverse process of decompression and cooling takes place as the air ascends the upcast shaft, the net effect is to raise the air temperature underground.

heat of crystallization

Heat evolved when unit weight of a salt crystallizes from a large amount of a saturated solution.

heat of hydration

The quantity of heat liberated or consumed when a substance takes up water.

heat of ionization

The quantity of heat that is absorbed when 1 g equivalent of a substance is broken up completely into positive and negative ions.

heat of mixture

That quantity of heat evolved when two liquids that do not react together are mixed. It is calculated from the temperature change and the specific heat of the mixture, and expressed in gram-calories per gram of mixture.

heat of reaction

The quantity of heat consumed or liberated in a chemical reaction as heat of combustion, heat of neutralization, or heat of formation. For example, the number of calories of heat absorbed when 1 g at wt of carbon reacts with 1 g mol wt of oxygen to form 1 g mol wt of carbon dioxide.

heat of transformation

The quantity of heat accompanying a constitutional change in a solid chemical compound or metal, e.g., the change from gamma to alpha iron. The temperature at which one crystalline form of a substance is converted into another solid modification is known as the transition point or transition temperature.

heat of wetting

Heat evolved or absorbed when a liquid and a solid surface are placed in contact.

heat pump

A mechanical refrigerating system used for air cooling in the warm season of the year, which, when the evaporator and condenser effects are reversed, absorbs heat from the outside air or water in the cold season of the year and raises it to a higher potential so that it also can be used for heating.

heat recuperation

The recovery of heat from waste gases.

heat sensitivity

A test that determines the flammability of explosives brought into contact with flame or heat.

heat transmission coefficient

See: coefficient of heat transmission.

heat-treated stone

A (gem) stone that has been artificially heated to change its color. Syn: heated stone; burnt stone.

heat unit

A unit of quantity of heat; the heat required to raise the unit mass of water through 1 degree of temperature. CF: calorie; British thermal unit.

heat value

The amount of heat obtainable from a fuel and expressed, for example, in British thermal units per pound.

heave

a. A rising of the floor of a mine caused by its being too soft to resist the weight on the pillars. See also: creep.

b. Upward movement of soil caused by expansion or displacement resulting from such phenomena as moisture absorption, removal of overburden, driving of piles, and frost action. c. Horizontal displacement of strata or other rocks along a fault, as opposed to the throw or vertical displacement. d. The horizontal component of the slip, measured at right angles to the strike of the fault. Used by J.E. Spurr and A. Geikie for offset. Used by Jukes Brown for strike slip. e. CF: upthrow. f. Displacement of mineral vein by faulting. Lifting of floor of underground working through rock pressure. g. Fault or throw in a lode. See also: throw.

heavily watered

Scot. Said of a colliery when the escape of water from the strata into the shaft or workings is abundant, requiring powerful pumping machinery.

heaving

Refers to the rising of the bottom after removal of the coal. See also: creep.

heaving shale

An incompetent or hydrating shale that runs, falls, swells, or squeezes into a borehole.

heavy crop

Gr. Brit. Collectively, the heavy minerals of a sedimentary rock.

heavy gold

Gold occurring as large particles. CF: nugget.

heavy ground

a. Closing or squeezing ground.

b. Dangerous hanging wall, which sounds hollow when rapped, indicating the possibility of a rock fall.

heavy joist

Timber over 4 in (10.2 cm) and less than 6 in (15.2 cm) in thickness and 8 in (20.3 cm) or over in width.

heavy liquid separation

Separation of ore particles by allowing them to settle through, or float above, a fluid of intermediate density.

heavy-media ore

See: natural ore.

heavy-media separation

A series of patented processes originally developed for the concentration of ore, but finding increased usage in coal cleaning. Suspension of magnetite (sp gr, 5.0) and ferrosilicon (sp gr, 6.7) are usually used for ore concentration; suspensions of magnetite for coal. The basic features of these processes as applied to coal are in the methods used for handling the magnetic medium. Specifications for magnetite should be somewhat as follows: l00% -100 mesh, 65% to 75% -325 mesh, 85% magnetics, and wet-ground in a ball or rod mill. See also: dense-media separation.

heavy metals

In exploration geochemistry, principally zinc, copper, cobalt, and lead, but under special conditions including one or more of the following metals: bismuth, cadmium, gold, indium, iron, manganese, mercury, nickel, palladium, platinum, silver, thallium, and tin.

heavy mineral

a. An accessory detrital mineral of a sedimentary rock, of high specific gravity, e.g., magnetite, ilmenite, zircon, rutile. CF: light mineral.

b. In igneous petrology, a mafic mineral. c. Resistant minerals that can be concentrated in the panning of alluvium and used as mineralogical and geochemical guides in prospecting.

heavy soil

A fine-grained soil, made up largely of clay or silt.

heavy spar

See: barite.

heavy tiff

Barite in southeast Missouri.

heavy water

Deuterium oxide, D (sub 2) O , in which D is the symbol for deuterium (heavy hydrogen or hydrogen 2). Water in which ordinary hydrogen atoms have been replaced by deuterium atoms. Natural water contains 1 heavy-water molecule per 6,500 ordinary water molecules. Deuterium oxide has a low neutron absorption cross section; hence, it is used as a moderator in some nuclear reactors.

hecatolite

See: moonstone.

hectare

A metric unit of land area equal to 10,000 m (super 2) , 100 ares, or 2.471 acres. Abbrev. ha.

hectorite

A monoclinic mineral, Na (sub 0.3) (Mg,Li) (sub 3) Si (sub 4) O (sub 10) (F,OH) (sub 2) ; smectite group. CF: montmorillonite.

hedenbergite

A monoclinic mineral, 4 ; pyroxene group; forms series with diopside and johannsenite; a common rock-forming mineral in iron-rich metamorphic rocks, limestone skarns, and fayalite-bearing plutonic rocks.

hedgehog stone

Quartz crystals containing needles of goethite or some other iron oxide. CF: hairstone.

hedging

The establishment of an opposite position on a futures market from that held and priced in the physical commodity. Without hedging, the physical position would be at risk to price fluctuations.

hedyphane

A hexagonal mineral, Pb (sub 3) Ca (sub 2) (AsO (sub 4) ) (sub 3) Cl ; apatite group; yellowish-white; at Franklin, NJ, and various localities in Sweden. CF: mimetite.

heel

a. A small body of coal left under a larger body as a support. Known also as heel of coal.

b. The mouth or collar of a borehole. c. The fixed jaw on an adjustable-wrench safety clamp or on a rock crusher. d. A floor brace or socket for wall-bracing timbers. e. The trailing edge of an angled blade. f. Any material remaining in a vessel after removal of the main portion of the contents.

heeling in

Temporary planting of trees and shrubs.

heel of a shot

a. In blasting, the face of a shot farthest away from the charge.

b. The distance from the mouth of the drill hole to the corner of the nearest free face; or that portion of the hole that is filled with the tamping; or that portion of the coal to be broken that is entirely outside the powder.

heep stead

The entire surface plant of the mine.

height of instrument

A surveying term used in spirit leveling for the height of the line of sight of a leveling instrument above the adopted datum, in trigonometric leveling for the height of the center of the theodolite above the ground or station mark, in stadia surveying for the height of the center of the telescope of the transit or telescopic alidade above the ground or station mark, and in differential leveling for the height of the line of sight of the telescope at the leveling instrument when the instrument is level. Abbrev. HI.

heinrichite

The arsenic analogue of uranocircite, Ba(UO (sub 2) ) (sub 2) (PO (sub 4) ) (sub 2) .12H (sub 2) O and its dehydration product with Ba(UO (sub 2) ) (sub 2) (AsO (sub 4) ) (sub 2) .8H (sub 2) O (metaheinrichite); occur near Lakeview, OR, and in the Black Forest, Germany. See also: arsenuranocircite; metaheinrichite.

heintzite

A hydrous borate of magnesium and potassium, colorless to white. Occurs in small crystals sometimes aggregated. From Stassfurt, Germany. Syn: hintzeite; kaliborite.

helenite

A wax near ozocerite but elastic like caoutchouc; yellow; sp gr, 0.915. It occurs at Ropa in Galicia. Syn: mineral caoutchouc.

helical bag conveyor

See: double helical bag conveyor.

helical conveyor

A conveyor for handling coal, grain, cement, or similar bulk materials. It comprises a horizontal shaft, with helical paddles or ribbons, which turn on its center line inside a stationary tube filled with the material. See also: worm conveyor.

helical steel support

A continuous screw-shaped steel joist lining for staple shafts. The lining is fixed to the ground by strata bolts rigidly fixed every 120 degrees without any yielding device. Developed in Germany and its use is claimed to effect considerable overall savings.

helicitic

Pertaining to a metamorphic-rock texture consisting of bands of inclusions that indicate original bedding or schistosity of the parent rock and cut through later-formed crystals of the metamorphic rock. The relict inclusions commonly occur in porphyroblasts as curved and contorted strings. The term was originally, but is no longer, confined to microscopic texture. Also spelled: helizitic. CF: poikiloblastic.

helictite

A distorted twiglike lateral projection of calcium carbonate, found in caves, etc. CF: stalactite; stalagmite. See: anemolite.

heliodor

A clear yellow variety of beryl found near Rossing, Namibia, and prized as a gemstone. Also spelled helidor. CF: golden beryl.

heliolite

A whitish to reddish-gray aventurine oligoclase with internal yellowish or reddish firelike reflections. Syn: sunstone.

heliotrope

a. A red-spotted, deep-green variety of chalcedony (cryptocrystalline quartz) used as a semiprecious stone. Syn: bloodstone. CF: plasma.

b. An instrument used in geodetic surveying to aid in making long-distance (as much as 320 km) observations; composed of one or more plane mirrors so mounted and arranged that a beam of sunlight is reflected toward a distant survey station where it is observed with a theodolite.

helium

An inert, monatomic, colorless, odorless element, the lightest of the rare gases. Except for hydrogen, helium is the most abundant element found in the universe. The bulk of the world's supply is obtained from wells. Symbol, He. Widely used in cryogenic research; vital in the study of superconductivity. Helium is used for arc welding, as a cooling medium for nuclear reactors, and as a gas for supersonic wind tunnels; extensively used for filling balloons as it is much safer than hydrogen. One of the recent largest uses for helium has been for pressuring liquid fuel rockets.

helizitic

See: helicitic.

helks

a. Large detached crags; a confused pile or range of rocks.

b. Bare tracts of limestone.

hellyerite

A triclinic mineral, NiCO (sub 3) .6H (sub 2) O ; occurs with zaratite at the Lord Brassey nickel mine, Heazlewood, Tasmania.

Helmholtz coil

A pair of similar coaxial coils with their distance apart equal to their radius, which permits an accurate calculation of the magnetic field between the coils. Used in calibration of magnetometers.

helper-up

See: pig tailer.

helvite

An isometric mineral, 2 ; manganese may be replaced by iron toward danalite, or by Zn toward genthelvite; forms tetrahedra; Mohs hardness, 6 to 6-1/2; in veins with quartz, hornblende, and iron oxide; in pegmatites, and some alkaline igneous rocks.

hemafibrite

A brownish-red to garnet-red, transparent to translucent, hydrous manganese arsenate, Mn (sub 3) (AsO (sub 4) )(OH) (sub 3) .H (sub 2) O ; soon turns black; Mohs hardness, 3; sp gr, 3.50 to 3.65; rare; from Nordmark, Sweden. Syn: aimafibrite.

Hematine

A copyrighted, confusing name for an imitation of hematite. Usually in the form of an imitation cuvette. Apparently an artificially processed friable mineral or other substance. Breaks easily. Mohs hardness, about 6.5; sp gr, 4.8; streak, black.

hematite

a. A trigonal mineral, alpha -Fe (sub 2) O (sub 3) ; red if earthy, reddish to bluish gray if massive, or bright metallic steel-gray in thin tablets or micalike flakes (specular hematite); invariably has red ocher streak. Kidney ore is massive reniform hematite. Commonly associated with quartz, oxyhydroxides such as goethite or limonite, and magnetite, after which it may be pseudomorphic; nonmagnetic when pure, but may appear magnetic due to residual or included magnetite or maghemite; the most widely mined ore of iron; in sedimentary rocks, Precambrian banded iron formations (including their metamorphosed equivalents), oolitic ironstones, contact-metamorphic deposits, commonly by alteration of magnetite; may be of secondary origin, having formed by oxidation and decomposition of iron silicates and carbonates; also occurs as a primary mineral in veins and replacement deposits associated with igneous intrusions, and in fumarolic deposits from volcanic gases. See also: iron ore; specularite. Syn: specular iron ore; oligist; oligist iron.

b. The mineral group corundum, eskolite, hematite, and karelianite.

hematite schist

See: itabirite.

hemetite

Any synthetic imitation of hematite.

hemi-

A prefix meaning half.

hemicrystalline

See: hyalocrystalline.

hemidome

The upper or lower two faces of a dome resulting from symmetry lower than that required for a dome in orthorhombic or monoclinic crystal systems.

hemihedral

In crystallography, having lower symmetry, resulting in forms with half the number of faces as the holohedral point group. CF: holohedral; merohedral.

hemimorphic

In crystallography, having no transverse plane of symmetry and no center of symmetry, and composed of forms belonging to only one end of the axis of symmetry.

hemimorphism

In crystallography, refers to minerals in crystal classes with merohedral symmetry such that crystal forms are different at opposite ends of the crystallographic axes, thus permitting polar crystal properties; e.g., hemimorphite, zincite.

hemiopal

See: semiopal.

hemipelagic

Sharing neritic and pelagic qualities.

hemipelagic-abyssal

Refers to sediments of the deep sea that contain terrestrial detritus.

hemiprism

A triclinic crystal form of two parallel faces with intercepts on two crystallographic axes.

hemipyramid

A monoclinic crystal form of two parallel faces with intercepts on three crystallographic axes. See also: pyramid.

hemitropic

Crystals that appear as if composed of two halves of a crystal turned partly round and united. Examples of this structure may often be found in feldspar and cassiterite crystals.

hemloite

A triclinic mineral, (As,Sb) (sub 2) (Ti,V,Fe) (sub 12) O (sub 23) (OH) ; metallic to submetallic black; in drill core samples associated with rutile, pyrite, molybdenite, and arsenopyrite at the Hemlo gold deposit, ON, Can.

hendersonite

An orthorhombic mineral, Ca (sub 3) V (sub 12) O (sub 32) .12H (sub 2) O ; in black fibrous crystals in Montrose County, CA, and San Juan County, NM.

Henderson process

The treatment of copper sulfide ores by roasting with salt to form chlorides, which are then leached out and precipitated.

hengleinite

A steel-gray iron sulfide with about 20% cobalt and nickel, (CoNiFe)S (sub 2) . Minute pyritohedral crystals; isometric. Probably a mixture of siegenite and pyrite. Formerly called cobaltnickelpyrite. From Musen, Westphalia, Germany. Syn: cobalt-nickel pyrite.

henry

Unit of electrical induction. With an electromotive force of 1 V and current of 1 A/s, one henry (H) = 10 (super 9) electromagnetic unit. Symbol H.

henryite

An isometric mineral, Cu (sub 4) Ag (sub 3) Te (sub 4) ; pale blue; associated with hessite, petzite, sylvanite, altaite, rickardite, and pyrite at Bisbee, AZ.

hepatic cinnabar

A mixture of cinnabar, bituminous material, and clay; liver-brown; may be flammable.

hepatic pyrite

a. See: marcasite.

b. See: pyrite.

hepatin

An amorphous limonite, of a liver-brown color, and containing a small percentage of copper.

hepatite

A variety of barite, so called from the fetid odor it exhales when heated.

heptaphyllite

Dioctahedral clay mineral. CF: octaphyllite.

heptavalent

Having a valence of 7. Also called septavalent; septivalent.

hercularc lining

A German method of lining roadways subjected to heavy pressures. It consists of a closed circular arch of specially shaped precast concrete blocks. The blocks, which are wedge-shaped, are made in two sizes for each lining and erected in such a way that alternate blocks offer their wedge action in opposite directions--the larger blocks toward the center of the roadway and the smaller outward. This arrangement gives a double-wedge effect so that part of the lateral pressure exerted by the strata on the lining is diverted axially along the roadway.

Hercules powder

Weak form of dynamite, based on nitroglycerin and a semiactive carrying dope.

Hercules stone

See: lodestone..

hercynite

An isometric mineral, 8 ; spinel group; forms series with magnesian spinel, with gahnite, and with chromite; massive or fine grained; Mohs hardness, 7.5 to 8; in metamorphosed argillaceous sediments with andalusite, sillimanite, or garnet; also in contact metamorphic deposits in limestone or marble; in some eruptive mafic rocks; may occur with corundum to form emery. Syn: ferrospinel.

herderite

A monoclinic mineral, 4 , with OH replacing F toward hydroxylherderite; pseudo-orthorhombic prismatic crystals or radiated fibrous aggregates; in late-stage pegmatites.

Herkimer diamond

Small, exceptionally clear, commonly doubly terminated quartz crystals in Herkimer County, NY; in cavities in sandstone and in loose earth or clay; also in mid-Atlantic beaches. Syn: Lake George diamond.

Heroult process

See: Hall process.

herrerite

Copper-stained blue and green smithsonite from Albarradon, Mexico.

Herreshoff furnace

A mechanical, cylindrical, multiple-deck muffle furnace of the McDougall type for smelting ores.

herringbone roller conveyor

A roller conveyor consisting of two parallel series of rolls having one or both series skewed. See also: roller conveyor. Syn: herringbone table.

herringbone stoping

Method used in flattish Rand stope panels 500 to 1,000 ft (152 to 305 m) long for breaking and moving ore. Stope is divided into 20-ft (6.1-m) panels, each worked by its own gang. A light tramming system delivers severed rock to a central scraper system.

herringbone table

See: herringbone roller conveyor.

herringbone texture

In mineral deposits, a pattern of alternating rows of parallel crystals, each row in a reverse direction from the adjacent one. It resembles the herringbone textile fabric.

hertz

A syn. for "cycles per second." Abbrev. Hz.

hess

S. Staff. Clinker from furnace boilers.

hessite

A monoclinic mineral, 4 , with gold replacing silver toward petzite; soft; metallic gray; fine grained, massive, or compact; sp gr, 8.24 to 8.45; in hydrothermal veins associated with quartz, pyrite, and native gold; a source of silver in California, Colorado, Ontario, Mexico, Chile, Romania, and Zimbabwe.

hessonite

An orange to yellow-brown gem variety of grossular. Syn: essonite; cinnamon stone.

hetaerolite

a. A very rare double oxide of zinc and manganese, ZnMn (sub 2) (super 3+) O (sub 4) , occurring in ore deposits as black tetragonal and fibrous crystals; hausmannite family.

b. A tetragonal mineral, ZnMn (sub 2) O (sub 4) ; forms bipyramids; may be fibrous; with zinc ores at Franklin, NJ, and near Leadville, CO. Also spelled heterolite.

hetero-

A prefix signifying various, or of more than one kind or form.

heteroblastic

Pertaining to a type of crystalloblastic texture in a metamorphic rock in which the essential mineral constituents are of two or more distinct sizes. CF: crystalloblastic; homeoblastic.

heterogeneous

a. Having more than one constituent or phase, thus exhibiting different properties in different portions.

b. A term describing metals and alloys with structures composed of more than one constituent. c. Unlike in character, quality, structure, or composition; consisting of dissimilar elements or ingredients of different kinds; not homogeneous.

heterogenite

a. A cobalt mineral, Co (super 3+) O(OH) , containing up to 4% CuO. Syn: stainierite.

b. Name suggested for all cobaltocobaltic hydroxides of varying purity.

heterogranular

a. Said of the texture of a rock having crystals of significantly different sizes.

b. Said of a rock having such a texture. Syn: inequigranular. c. See: anisodesmic.

heteromorphic

Said of igneous rocks having similar chemical composition but different mineralogic composition.

heteromorphism

The crystallization of two magmas of nearly identical chemical composition into two different mineral aggregates as a result of different cooling histories.

heteropic

Said of sedimentary rocks of different facies, or said of facies characterized by different rock types. The rocks may be formed contemporaneously or in juxtaposition in the same sedimentation area or both, but the lithologies are different; e.g., facies that replace one another laterally in deposits of the same age. Also, said of a map depicting heteropic facies or rocks. CF: isopic.

heterothrausmatic

A descriptive term applied to igneous rocks with an orbicular texture in which the nuclei of the orbicules are composed of various kinds of rock or mineral fragments. CF: crystallothrausmatic; isothrausmatic; homeothrausmatic.

heterotomous

Having a cleavage unlike that characteristic of the mineral in its ordinary form, as a variety of feldspar.

heugh

a. Scot. A place where coal or other mineral is worked; a pit or shaft. Also spelled heuch.

b. The steep face of a quarry or other excavation. c. A glen with rugged sides; a crag. d. An old English term for coal seams or coal workings.

heulandite

A monoclinic mineral, (Na, Ca) (sub 2-3) Al (sub 3) (Al, Si) (sub 2) Si (sub 13) O (sub 36) .12H (sub 2) O] ; zeolite group, with extensive substitution of NaSi for CaAl and K predominant over Na; forms in cavities in basalt and andesite, as skarn druses, as diagenetic product in silicic vitreous tuffs, in bentonitic clays, and as authigenic mineral in limestone or sandstone.

hewer

a. Eng. In the Newcastle coalfield, one who undercuts the coal with a pick. A coal miner.

b. N. of Eng. One who may use a hand pick but usually uses a pneumatic (windy) pick to win coal. Task consists of breaking in or making a nicking, digging out the coal, and filling onto a conveyor belt or into tubs.

hewettite

A monoclinic mineral, CaV (sub 6) O (sub 16) .9H (sub 2) O ; forms deep red microscopic needles in vanadium deposits near Cerro de Pasco, Peru, and Paradox Valley, CO.

hewing

a. Eng. In the Newcastle coalfield, undercutting or mining the coal. Syn: breaking in.

b. The dressing of timber by chopping or by blows from an edged tool.

hewing double

Eng. See: double working.

hexad

A crystallographic axis of rotation of 60 degrees , a sixfold axis. CF: axis of symmetry.

hexagonal

a. A geometrical form of six sides; e.g., hexagonal prism, hexagonal pyramid.

b. The crystal system characterized by a unique hexad (sixfold axis of rotation.) CF: crystal systems.

hexagonal close-packed crystals

Crystals having atoms at the corners of the hexagonal unit cells that are right prisms with rhombic bases, and at the corners of those (isosceles) triangular prisms that are similarly located halves of the hexagonal unit cells. The two sets of atoms are not crystallographically equivalent.

hexagonal system

In crystallography, that system of crystals in which the faces are referred to four axes--a principal or vertical axis and three lateral axes perpendicular to the vertical axis and intersecting at mutual angles of 60 degrees . CF: trigonal; trigonal system.

hexagonite

A lavender variety of manganoan tremolite.

hexahydrite

The mineral group bianchite, ferrohexahydrite, hexahydrite, moorhouseite, and nickel-hexahydrite.

hexavalent

a. Having a valence of 6.

b. Having six valences; e.g., manganese with valences of 1, 2, 3, 4, 6, and 7.

Hexhlet sampler

A selective mine dust-sampling instrument. It collects the airborne dust sample in two components. The fraction larger than 5 mu m in size is separated from the total cloud in a size selector. The instrument collects some grams of respirable dust by filtration of the mine air through a fine pore ceramic thimble. See also: thermal precipitator.

Heyn's reagent

An etching reagent containing 10% copper ammonium chloride in water.

hiatal

a. Said of the texture of an igneous rock in which the sizes of the crystals are not in a continuous series but are broken by hiatuses, or in which there are grains of two or more markedly different sizes, as in porphyritic rocks. CF: seriate.

b. Pertaining to or involving a stratigraphic hiatus.

hiatus

a. A break or interruption in the continuity of the geologic record, such as the absence in a stratigraphic sequence of rocks that would normally be present but either were never deposited or were eroded before deposition of the overlying beds.

b. A lapse in time, such as the time interval not represented by rocks at an unconformity; the time value of an episode of nondeposition or of nondeposition and erosion together.

Hicks' hydrometer

An instrument consisting of a series of colored glass beads of different densities contained in a glass tube for testing the specific gravity of electrolytes.

hiddenite

An emerald-green to yellow-green gem variety of spodumene. See also: spodumene. Syn: lithia emerald.

hide salt

Coarse sizes of rock salt, usually No. 2 or No. 1.

high

a. The crest or culmination of a structure, such as a dome or an anticline. CF: low. Syn: structural high.

b. Name for the coal of a thick seam. c. A geophysical anomaly with values greater than normal; e.g., a gravity maximum or a geothermal maximum.

high-alumina refractories

Alumina-silica refractories containing 45% or more alumina.

high-angle fault

A fault with a dip greater than 45 degrees . CF: low-angle fault.

high-carbon steel

Carbon steel that contains more than 0.5% carbon.

high-conductivity copper

Metal of high purity, having an electrical conductivity not much below that of the international standard, which is a resistance of 0.15328 Omega for a wire 1 m long and weighing 1 g.

high doors

Scot. An upper landing in a shaft.

high-expansion foam

A method of fighting underground fires developed in the United States, and somewhat similar to the British foam plug. It involves the formation of a high-expansion noncombustible foam. Large volumes of the foam are drawn or blown over and around the fire until it can no longer be sustained due to lack of oxygen. The foam is made from ammonium lauryl sulfate and 1 gal (3.8 L) of solution is used for each 250 to 300 ft (super 3) /min (7.1 to 8.5 m (super 3) /min) of air passing through the net.

high explosive

An explosive that is capable of detonating. There are two main types: (1) primary explosives, which detonate no matter what type of stimulus is given--these usually are very sensitive and (2) secondary explosives, which detonate normally only when the stimulus is a strong shock--under other types of stimulus they may merely deflagrate.

high feed

See: fast gear.

high furnace

The ordinary blast furnace.

high-grade

a. Said of an ore with a relatively high ore-mineral content. CF: low-grade.

b. To steal rich or specimen ore. c. An arbitrary designation for dynamite of 40% strength or over. See also: grade.

high-grade mill

A plant for treating high-grade ores.

high-grading

Theft of valuable pieces of ore. See also: gouging.

high-level placer

A placer on an alluvial terrace.

highmoor peat

Peat occurring on high moors and formed predominantly of moss, such as sphagnum. Its moisture content is derived from rain water rather than from ground water and is acidic. Mineral matter and nitrogen content are low, and cellulose content is high. Syn: moorland peat; moor peat; moss peat.

high-phosphorus ores

Ores containing from 0.18% to 1.0% phosphorus.

high pillar

See: shaft pillar.

high quartz

Phase of quartz stable from 867 to 1,470 degrees C. Also called beta quartz. See also: quartz.

high-raise miner

See: miner.

high-rank coals

Coals containing less than 4% of moisture in the air-dried coal or more than 84% of carbon (dry ash-free coal). All other coals are considered as low-rank coals.

high-rank metamorphism

Metamorphism accomplished under conditions of high temperature and pressure. See also: metamorphic grade.

high-ratio resistance controller

This controller gives a high ratio of maximum to minimum resistance, 6,000:1. A high resistance is thus available for reverse-current braking, but the design ensures that there is an ample volume of electrolyte between the electrodes when starting at twice full-load torque. It is similar to the swinging-electrode controller.

high reef

The bedrock or reef rising from the lowest and richest part of an alluvial placer and forming the slopes of the ancient valley.

high-reef wash

Deposits of wash dirt upon the high reef.

high-resolution seismic technique

A seismic prospecting technique in which a special recording system yields readable reflections from layers less than 10 ft (3 m) thick at depths as little as 100 ft (30 m).

high seas

The entire world's oceans except for the portion lying shoreward of the outer limit of the territorial seas.

high side

A deep coal-mine car, i.e., one with high sides. CF: gondola.

high-silica ore

See: natural ore.

high sintering

Synonymous with advanced sintering at high temperatures, usually the final sintering close to the melting point of the material.

high-temperature bonding mortar

A mixture of refractory materials, either raw or calcined, to which other materials not classified as refractory materials have been added for the purpose of increasing the plasticity, giving air-setting properties, and lowering the temperature at which the bond develops.

high-tensile steel

A type of structural steel having a maximum yield point of 23 st/in (super 2) as compared with 15.25 st/in (super 2) for mild steel. See also: yield stress.

high-tension line

A high-voltage transmission line.

high-tension separation

In mineral processing, the use of high-voltage direct current at between 18,000 V and 80,000 V to charge small particles of dry material as they fall through its field (emanating as a spray or a point discharge). These are then sorted into relatively charge-retaining and charge-losing minerals in accordance with their conducting power. Also called electrostatic separation.

high velocity

See: velocity.

high volatile A bituminous coal

The rank of coal, within the bituminous class of the Classification D 388, such that on the dry and mineral-matter-free basis, the volatile matter content of the coal is greater than 31% (or the fixed carbon content is less than 69%), and its gross calorific value is equal to or greater than 14,000 Btu/lb (32.54 MJ/kg) of coal on the moist, mineral-matter-free basis, and the coal is commonly agglomerating.

high volatile B bituminous coal

The rank of coal, within the bituminous class of Classification D 388, such that, on the moist mineral-matter-free basis, the gross calorific value of the coal in British thermal units per pound is equal to greater than 13,000 (30.24 MJ/kg) but less than 14,000 (32.54 MJ/kg) and the coal commonly agglomerates.

high volatile C bituminous coal

The rank of coal, within the bituminous class of Classification D 388, such that, on the moist, mineral-matter-free basis, the gross calorific value of the coal in British thermal units per pound is equal to or greater than 11,500 (26.75 MJ/kg) but less than 13,000 (30.24 MJ/kg) and the coal commonly agglomerates, or equal to or greater than 10,500 (24.42 MJ/kg) but less than 11,500 (26.75 MJ/kg) and the coal agglomerates.

high-volatile coals

Coals containing over 32% volatile matter with a coal rank code No. 400 to 900. See also: coal classification.

high voltage

a. A high electrical pressure or electromotive force.

b. In coal mining, voltages above 1,000 V. CF: low voltage; medium voltage.

highwall

The unexcavated face of exposed overburden and coal or ore in an opencast mine, or the face or bank on the uphill side of a contour strip mine excavation.

high-water level

The plane of high water.

highwoodite

A dark-colored intrusive rock composed of alkali feldspar, labradorite, pyroxene, biotite, iron oxides, apatite, and possibly a small amount of nepheline. It is essentially a monzonite. Its name, given by Johannsen in 1938, is derived from the Highwood Mountains, MT. Not recommended usage.

hilgardite

Hydrated chloroborate of calcium, Ca (sub 2) B (sub 5) O (sub 9) Cl.H (sub 2) O , as colorless monoclinic-domatic crystals in the rock salt of Louisiana. See also: parahilgardite.

hill

a. An arch or high place in a mine.

b. Scot. The surface at a mine. c. N. of Eng.; Mid. An underground inclined plane. d. A natural elevation of land of local area and well-defined outline.

hill-and-dale formation

Applied to the ridges and hollows along the surface of dumped material (usually overburden) at an opencast mine. The undulations are leveled out when the land is restored.

hillock

A small, low hill; a mound. Adj: hillocky.

hill peat

Peat formed in mountainous districts and characterized by the presence of Sphagnum, Andromeda, heath, pine trees, etc.

hillside

a. Used to describe quarries when located in high slopes. CF: terrain slope.

b. A part of a hill between its crest and the drainage line at the foot of the hill. Syn: hillslope.

hillside placers

Gravel deposits intermediate between the creek and bench gravels; their bedrock is slightly above the creek bed, and the surface topography shows no indication of benching.

hillside quarry

A quarry cut into and along the hillside; may comprise a single face or a series of benches. If the depth of face is not more than about 30 ft (9 m) it can be worked in one cut, but deeper faces are usually worked in two or more benches. See also: pit quarry.

hillslope

See: hillside.

Hilt's law

A generalization that states that, in a vertical sequence at any given point in the coalfield, the rank of the coal of the successive seams rises with increasing depth. Although this statement is generally true, there are numerous departures from it.

hindered settling

a. In classification, when the minerals settle in a thick pulp, as opposed to free settling in which the free particles fall through fluid media.

b. Settlement of particles through a crowded zone, usually in a hydraulic column through which their fall is opposed by rising water.

hindered-settling ratio

The ratio of the apparent specific gravities of the mineral against the suspension (not against the liquid) raised to a power between one-half and unity.

hindostan

A fine-grained sandstone used extensively in the manufacture of very cheap sharpening stones, esp. axstones. Found in Indiana.

hinge

The locus of maximum curvature or bending in a folded surface, usually a line. Syn: flexure.

hinged apron

See: apron conveyor.

hinged apron pan

An apron pan that is made with a hinge construction along each edge so that it may be joined to companion pans by a hinge pin or through a rod.

hinged bar

Steel bars placed in contact with the roof and at right angles to the longwall face. They are usually supported by yielding steel props. The bar can be extended to support newly exposed roof by adding another bar, which can be locked onto it by a simple wedge or pin arrangement. The hinged bar is widely used on conveyor faces in continuous mining.

hinged-hammer crusher

See: Williams' hinged-hammer crusher.

hinge fault

A fault on which the movement of one side hinges about an axis perpendicular to the fault plane; displacement increases with distance from the hinge. It is a questionable term. CF: scissor fault; rotational fault.

hinterland

a. A subjective term referring to the relatively undisturbed terrain on the back of a folded mountain range; i.e., the side away from which the thrusting and folding appears to have taken place.

b. The land that lies behind a seaport or seaboard and supplies the bulk of its exports and absorbs the bulk of its imports.

hintzeite

See: heintzite.

hircite

A yellowish-brown, amorphous hydrocarbon found in Burma, which emits a bad smell on burning.

Hirschback method

A method for draining combustible gases from coal seams in which superjacent entries are developed over the coal seam being mined. The entries are located from about 80 to 138 ft (24 to 42 m) above the seams to be mined and are often supplemented with up or down boreholes drilled perpendicular to the walls of the entries. Also known as the superjacent roadway system.

hisingerite

A monoclinic mineral, Fe (sub 2) Si (sub 2) O (sub 5) (OH) (sub 4) .2H (sub 2) O ; fine-grained to cryptocrystalline or fibrous; at Hibbing, MN; Blaine County, ID; and in Canada, Greenland, Finland, and Sweden.

histogram

A vertical-bar graph representing a frequency distribution, in which the height of bars is proportional to frequency of occurrence within each class interval and, due to the subdivision of the x-axis into adjacent class intervals, there are no empty spaces between bars when all classes are represented in a sample so graphed. Histograms are used to depict particle-size distribution in sediments.

historical geology

A major branch of geology that is concerned with the evolution of the Earth and its life forms from its origins to the present day. The study of historical geology therefore involves investigations into stratigraphy, paleontology, and geochronology, as well as the consideration of paleoenvironments, glacial periods, and plate-tectonic motions. It is complementary to physical geology. Not to be confused with history of geology. See also: geology.

hit

Eng. To find, prove, or cut into a coal seam or fault.

hitch

a. Step cut in rock face to hold timber support in underground working. Syn: stip.

b. N. of Eng. A minor geological fault or roll in the coal seam. c. Scot.; Eng. A minor dislocation of a vein or stratum not exceeding in extent the thickness of the vein or stratum. d. A hole cut in the side rock, when this is solid enough to hold the cap of a set of timbers permitting the leg to be dispensed with. e. A fault. Fractures and dislocations of strata common in coal measures, accompanied by more or less displacement. f. A connection between two machines. g. To attach trams to hauling ropes by short chains. h. A sudden stoppage of pumping machinery. i. To dig or pick holes or places to receive the ends of timbers.

hitch-and-step

a. S. Wales. A system of regulating the distance between the faces of stalls in longwall work.

b. See: stepped longwall.

hitch cutter

A miner who cuts places in the coal, ore, or wall in which to rest or place timbers to prevent rock from falling.

hitcher

a. The person who runs trams into or out of the cages, gives the signals, and attends at the shaft when miners are riding in the cage. See also: cager.

b. One who works at the bottom of a haulage slope or plane, engaging the clips or grips by means of which mine cars are attached to a hoisting cable or chain used for haulage up a steep incline to the mine surface. Also called hitcher-on. See also: hitcher-on; onsetter.

hitcher-on

The person employed at the bottom of a shaft or slope to put loaded cars on, and take empty cars off the cage. See also: hitcher.

hitch timbering

Installing bars in hitches either cut or drilled in the rib, thereby eliminating the need for legs. Hitch holes may be provided for each individual bar.

Hi-Velocity gelatin

Explosive containing low-density gelatin; used for submarine blasting.

hjelmite

A former name for yttromicrolite.