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Appendix:Dictionary of Mining, Mineral, and Related Terms/R/3

renardite
 * An orthorhombic mineral, Pb(UO (sub 2) ) (sub 4) (PO (sub 4) ) (sub 2) (OH) (sub 4) .7H (sub 2) O that may be the mineral dewindtite; at Kasolo, Zaire.

rending
 * The breaking of coal into lumps with a minimum of smalls. The relative slowness of low explosives makes them suitable for rending coal since they lack the greater shattering power of high explosives.

rendrock
 * A dynamite used in blasting and consisting of nitroglycerin, potassium nitrate, wood pulp, and paraffin or pitch.

renierite
 * A tetragonal mineral, (Cu,Zn) (sub 11) (Ge,As) (sub 2) Fe (sub 4) S (sub 16) ; pseudocubic; a possible source of germanium. (Not reinerite.)

reniform
 * Kidney-shaped. Said of a crystal structure in which radiating crystals terminate in rounded masses; also said of mineral deposits having a surface of rounded, kidneylike shapes. CF: colloform; colloid minerals; botryoidal.

Renn-Walz process
 * A method of reclaiming iron and other metals from the waste materials produced in the smelting of zinc and lead ores. The process differs from the Krupp-Renn method in that it is a volatilization process for recovering molten metals in oxide form. The metal vapors are oxidized by excess air and carried off in the flue gases from which they are subsequently filtered.

rensselaerite
 * A compact fibrous variety of talc pseudomorphous after pyroxene; harder than talc; polishes well; made into ornamental objects; in northern New York and Canada.

rent and royalty
 * a. The amount paid by a coal mining operator to the owner of the coal for each ton of coal mined and usually expressed in cents per ton.

b. In mining leases, words used interchangeably to convey the same meaning.

reopening sealed area
 * There are four methods used in reopening sealed-off areas in a mine: (1) the direct method in which the stoppings are breached and air is circulated around the district without previous inspection by a rescue team; (2) the prior-inspection method in which prior inspection of the whole district by a rescue team is followed by circulation of air around the district; (3) the stage method in which the ventilation is restored and the enclosed gases are removed in successive stages; and (4) the partial-reopening method which is adopted when it is required to recover part of a district but leave the remainder sealed off.

repairman
 * A worker whose duty it is to repair tracks, doors, brattices, or to reset timbers, etc., under the direction of a foreman. Also called repairer.

repeated twinning
 * Crystal twinning involving more than two individuals. Syn: multiple twin. CF: polysynthetic twinning; twin laminae; cyclic twinning.

replaceable hydrogen
 * Hydrogen atoms in acid molecule that can be replaced by those of metal.

replaceable insert
 * Diamond inset plates and other geometric forms fastened to and/or supported by the bit blank by brazing or mechanical locking so that in drilling they may be replaced when diamond wear exceeds a specified amount.

replaceable pilot
 * A central interchangeable pluglike portion of a noncoring bit protruding or leading the outside portion of such bits. See also: pilot.

replacement
 * a. Change in composition of a mineral or mineral aggregate, presumably accomplished by diffusion of new material in and old material out without breakdown of the solid state.

b. A process of fossilization involving substitution of inorganic matter for the original organic constituents of an organism.

replacement bit
 * See: reset bit.

replacement deposit
 * A mineral deposit that has been formed by deposition from mineral solutions taking the place of some earlier, different substance.

replacing switch
 * A device consisting of a united pair of iron plates hinged to shoes fitting over the rails to replace, on the track, derailed railway rolling stock. Also used for mine cars.

replica
 * A filling of mineral material deposited by percolating ground waters in external molds, thus reproducing the original exterior of the fossil shell or other object, with its exact size and shape.

replicate sampling
 * Taking each sample in a number of subsamples by putting increments in turn into different containers, in order to estimate the sampling accuracy. The same total weight of sample is collected whether or not replicate sampling is employed.

repose angle
 * The angle between the horizontal and the surface slope of any pile of material formed by free fall of the material.

representation work
 * Assessment work on a mining claim.

representative fraction
 * The scale of a map, expressed in the form of a numerical fraction that relates linear distances on the map to the corresponding actual distances on the ground, measured in the same units (centimeters, inches, feet); e.g., 1/24,000 indicates that one unit on the map represents 24,000 equivalent units on the ground. Abbrev: RF.

representative sample
 * In testing or valuation of a mineral deposit, samples large enough and average in composition as to be considered representative of a specified volume of the surrounding orebody. Blended large samples from different exposures are not necessarily representative, since the mineral structure may have varied so as to introduce special problems from area to area in treatment.

rerailer
 * A small lightweight device, used in pairs that straddle and are locked to each of the rails to retrack railroad cars and locomotives. Of Y-shaped design, they permit both wheels to be retracked from either or both sides of the rail at the same time. As the car is pulled across the device, the derailed wheels are channeled back onto the tracks. Also called retracker. See also: frog.

rescue
 * To move live workers or dead bodies from a mine after a mine disaster. Sometimes called recover. The latter applies esp. to putting the mine in shape for operation again.

rescue apparatus
 * A name applied to certain types of apparatus worn by workers, permitting them to work in noxious or irrespirable atmospheres such as obtained during mine fires, following mine explosions, as a result of accidents in ammonia plants, from smelter fumes, etc. Oxygen compressed in a cylinder, a regenerating substance to purify the breathed air, and a closed system constitute the general principle of the apparatus. See also: mine rescue apparatus.

rescue-car
 * See: mine rescue car.

rescue station
 * Mine chamber equipped with rescue gear, including oxygen apparatus, and manned by trained rescue workers.

rescue team
 * A team of workers, from five to eight strong, trained in the use of breathing apparatus and in rescue operations after colliery explosions or mine fires. The team trains every week or so at a rescue station.

research
 * Word often misused. Two broad meanings are reexamination of previously accepted data in the light of current expansion of basic knowledge; and search in reality, specific to an entirely novel concept and calling for development of new approaches. Wrongly defined when descriptive of original rehash.

resection
 * a. A method in surveying by which the horizontal position of an occupied point is determined by drawing lines from the point to two or more points of known position. Syn: intersection.

b. A method of determining a plane-table position by orienting along a previously drawn foresight line and drawing one or more rays through the foresight from previously located stations.

resequent fault-line scarp
 * A fault-line scarp in which the structurally downthrown block is also topographically lower than the upthrown block. CF: obsequent fault-line scarp.

reserve
 * a. The quantity of mineral that is calculated to lie within given boundaries. It is described as total (or gross), workable, or probable working, depending on the application of certain arbitrary limits in respect of deposit thickness, depth, quality, geological conditions, and contemporary economic factors. Proved, probable, and possible reserves are other terms used in general mining practice.

b. Sampled ore, developed, blocked out, or exposed on not less than three sides. See also: development sampling; ore reserve; probable ore; workable. c. The amount of payable ore, developed and ready for extraction, or blocked out ahead of immediate requirements.

reserve base
 * That part of an identified resource that meets specified minimum physical and chemical criteria related to current mining and production practices, including those for grade, quality, thickness, and depth. The reserve base is the in-place demonstrated (measured plus indicated) resource from which reserves are estimated. It may encompass those parts of the resources that have a reasonable potential for becoming economically available within planning horizons beyond those that assume proven technology and current economics. The reserve base includes those resources that are currently economic (reserves), marginally economic (marginal reserves), and some of those that are currently subeconomic (subeconomic resources). The term geologic reserve has been applied by others generally to the reserve-base category, but it also may include the inferred-reserve-base category; geologic reserve is not part of this classification system.

reserved coal
 * Coal reserved from lease, as coal under buildings.

reserved lands
 * Defined by the U.S. Department of the Interior as "federal lands which are dedicated or set aside for a specific public purpose or program and which are, therefore, generally not subject to disposition under the operation of all the public land laws."

reserved mineral
 * Economic minerals that are not the property of the landowner but belong to the State. The State confers the right to prospect for and to mine these minerals on any one who applies for this right on the form prescribed and at the competent mining office. Such minerals as coal and iron ores are included in this group. CF: unreserved mineral.

reserves
 * a. An estimate within specified accuracy limits of the valuable metal or mineral content of known deposits that may be produced under current economic conditions and with present technology.

b. That part of the reserve base that could be economically extracted or produced at the time of determination. The term reserves need not signify that extraction facilities are in place and operative. Reserves include only recoverable materials; thus, terms such as extractable reserves and recoverable reserves are redundant and are not a part of this classification system. Syn: mineral reserves. See also: measured resources.

reset action (nonstandard)
 * In flotation, the component of control action in which the final control element is moved at a speed proportional to the extent of proportional position action. This term applies only to a multiple action including proportional position action.

reset bit
 * A bit made by reusing the sound diamonds salvaged from a used drill bit and setting them in the crown attached to a new bit blank. Some new diamonds usually are added to those salvaged, since generally not all of the salvaged or recovered stones are reusable. Syn: replacement bit.

resettable
 * A salvaged diamond or used diamonds in good condition; hence, diamonds that can be used again by being reset in another tool or bit. Also called usable diamond; usables; usable stone.

resetting
 * a. The act or process of producing a reset bit. See also: reset bit.

b. To rerun a casing string into a borehole by placing its bottom end at a lower point in the hole.

residual
 * a. Characteristic of, pertaining to, or consisting of residuum; remaining essentially in place after all but the least soluble constituents have been removed.

b. Standing, as a remnant of a formerly greater mass of rock or area of land, above a surrounding area that has been generally planed; said of some rocks, hills, mesas, and groups of such features.

residual arkose
 * See: grus.

residual boulder
 * A boulder of local origin produced by weathering and standing in locally derived soil or grus.

residual clay
 * Clay material formed in place by the weathering of rock, derived either from the chemical decay of feldspar and other rock minerals or from the removal of nonclay-mineral constituents by solution from a clay-bearing rock (such as an argillaceous limestone); a soil or a product of the soil-forming processes. CF: primary clay; secondary clay.

residual element
 * An element present in an alloy or other material in small quantities after some type of treatment, but not added intentionally.

residual errors
 * The differences between measured values and the most probable value.

residual field
 * a. See: residual magnetic field.

b. The field remaining after subtraction of an average or background field (e.g., gravity, magnetic).

residual gravity
 * In gravity prospecting, the portion of a gravity effect remaining after removal of some type of regional variation; usually the relatively small or local anomaly components of the total or observed gravity field.

residual liquid
 * A late-stage magmatic fluid. Syn: rest magma.

residual magnetic field
 * a. The magnetic field that remains in a part after the magnetizing force is removed.

b. See: residual field.

residual magnetism
 * a. In magnetic prospecting, the portion of a magnetic effect remaining after removal of some type of regional effect; usually the relatively small or local anomaly components of the total or observed magnetic field.

b. The magnetism remaining in a substance after the magnetizing force has been removed. See also: remanence.

residual minerals
 * The rock-forming minerals that are either stable in the surface environment or unstable but react so slowly that they are not appreciably broken down.

residual oil
 * a. The amount of liquid petroleum remaining in a formation at the end of a specified production process.

b. Liquid or semi-liquid products obtained as residues from the distillation of petroleum. They contain the asphaltic hydrocarbons. Residual oils are also known as asphaltum oil, liquid asphalt, black oil, petroleum tailings, and residuum.

residual ore deposit
 * An accumulation of valuable minerals, formed by the natural removal of undesired constituents of rocks or conversion of useless to useful components.

residual placer
 * See: residual ore deposit.

residuals
 * The elements ordinarily present in steel in small quantities without definite intent on the part of the steel maker.

residual stress
 * The stress that exists in an elastic solid body in the absence of, or in addition to, stresses caused by an external load. Such residual stress may be due to: (1) deformation, caused by cold-working, as in drawing or stamping; (2) change in the specific volume due to thermal expansion, a phase change, or magnetostriction; (3) by the joining together of structural parts by force, such as welding.

residue
 * a. The waste or final product from a hydrometallurgical plant.

b. S. Afr. The amount of valuable matter remaining in ore after treatment, in percent or pennyweights per ton. c. As applied to proximate analysis of coke, a calculated figure obtained by subtracting the sum of the percentages of moisture in the analysis sample, volatile matter, and ash from 100. d. That which remains after a part has been separated or otherwise treated. e. See: rock fracture.

residuite
 * a. The constituent petrological unit or maceral occurring as characteristic unresolvable granular and translucent groundmass in clarain.

b. Same as residuum.

residuum
 * a. Weathered material, including the soil, down to fresh, unweathered rock.

b. Material resulting from the decomposition of rocks in place and consisting of the nearly insoluble material left after all the more readily soluble constituents of the rocks have been removed. c. The structureless groundmass of microscopically unresolvable constituents, consisting of particles of one to two microns or less, usually opaque, and of a dark color. It is the same as the lower range of fine micrinite. See also: residue.

resilience
 * The ability of a material to store the energy of elastic strain. This ability is measured in terms of energy per unit volume.

resilient couplings
 * The resilient type of coupling has many designs but essentially has torsional response to application or variation of the transmitted load. For the all-metal types, the resilient element may be in the form of laminated spring packs or a cylindrical grid member, connecting the driver and driven hubs. Resilience damps shock loads and also provides means of keeping gear teeth in contact, compensating for small errors in gear cutting. Other types use rubber or rubberlike material that may be in the form of a spider, segmental blocks, a number of balls, or a molded disk with metal inserts, providing the connection between the driver and driven hubs.

resiliometer
 * A device for testing resilience.

resin
 * a. One of various hard, brittle, transparent or translucent solids formed esp. from plant secretions and obtained as exudates of recent or fossil origin, such as conifers and certain tropical trees, by condensation of fluids on loss of volatile oils. Resins are yellowish to brown with resinous luster; fusible and flammable; soluble in ether and other organic solvents, but not in water; and represent a complex mixture of terpenes, resin alcohols, and resin acids and their esters. CF: amber; fossil resin. See also: mineral resin. Syn: natural resin.

b. A synthetic addition or condensation polymerization substance or natural substance of high molecular weight, which under heat, pressure, or chemical treatment becomes moldable. See also: bead; beads.

resin-anchored bolts
 * A passive roof-bolting technique in which a rebar-type bolt is anchored in resin. A two-part resin cartridge is placed at the back of a hole and is mixed as the bolt is inserted and rotated. The bolt is forced tight against the roof until the resin sets.

resin-in-pulp
 * An ion exchange process applied in acid-leach slurry from which abrasive particles of sand have been removed. Abbrev., R.I.P.

resin-in-pulp (RIP) process
 * The method in which pulp is classified to remove the sands, and the resin adsorbs the metal directly from the slime pulp without the necessity of thickening or filtering. It is esp. adapted for ores that do not settle readily, and where thickening and filtration are difficult.

resinite
 * A maceral of coal within the exinite group, consisting of resinous compounds, often in elliptical or spindle-shaped bodies representing cell-filling matter or resin rodlets. CF: cutinite; sporinite.

resinite coal
 * This coal consists of more than 50% of small resin bodies embedded in gelito-collinite, fusinito-collinite, or in collinite of fusinitic nature. The resin bodies differ in shape and may be angular, spheroidal, or lenticular. Varying in size, they may be visible to the unaided eye in a hand specimen of coal or only distinguishable under the microscope. Resinite coal may also contain small quantities of microspores, fine fragments of fusinized tissue, and, not infrequently, broad streaks of vitrinite. Hand specimens of resinite coal are matt or semimatt and in coals of low rank are brown or brownish-black. On fractures perpendicular to the bedding, the resin bodies appear rounded, black, and lustrous; in the bedding planes themselves they frequently appear as matt rodlets. Resinite coals frequently are high in ash.

resin jack
 * See: sphalerite. Also spelled rosin jack.

resinoid
 * A coal constituent similar to material derived from resin.

resinous
 * a. Resembling resin, as opal, and some yellow varieties of sphalerite.

b. The luster on fractured surfaces of minerals, e.g., opal, sulfur, amber, and sphalerite, and rocks, e.g., pitchstone. CF: vitreous.

resinous coal
 * Coal in which the attritus may contain a large proportion of resinous matter. Coals of this type are found more often among the younger coals.

resin rodlets
 * A fossil resinous secretion that may be isolated from coal. It was presumably deposited in a resin duct by a secretory epithelium.

resin tin
 * See: cassiterite. Also spelled rosin tin.

resistance
 * a. When an air current flows through a mine it meets with frictional resistance from the roof, sides, and floor. The amount of this resistance depends upon the extent and nature of the rubbing surface, the area of the airways, and the velocity of the air. See also: Atkinson.

b. In flotation, a property opposing movement of material or flow of energy, and involving loss of potential (voltage, temperature, pressure, and level). c. The property of an electrical circuit that opposes the flow of a current and is measured in ohms. Syn: thermal resistance.

resistance methanometer
 * A version of the catalytic methanometer with the addition of improved detector elements. Platinum may be used as the filament that both heats the detecting element and acts simultaneously as a resistance type thermometer. Gas is drawn through the instrument by a rubber suction bulb, and the filaments are heated from a dry battery of the mercury type contained in the apparatus. Readings of methane concentration can be taken on the built-in electrical meter.

resistance of detonator
 * As applied to electric blasting caps, the total resistance of the leg wires and the bridge wire.

resistance strain gage
 * See: electrical resistance strain gage.

resistance to blasting
 * Specific value of the resistance of the rock to the explosive force, determined by trial blasting. It is a function of maximum burden, hole depth, quantity of explosive (degree of packing), and throw.

resistivity
 * a. Resistance, R, of a block of specified material in terms of units of length 1 and cross section a. Unit volume is 1 cm (super 3) of the material concerned, and the resistivity measurement is made during electrical prospecting. Specific resistance = (Ra) / 1.

b. The electrical resistance offered to the passage of a current. Usually expressed in ohm meters, which is the electrical resistance of a column of fluid 1 m long and 1 m (super 2) in cross section. c. The opposite of conductivity of an electrical current passing through fluid-bearing rock formations. d. The electrical resistance between opposite faces of a 1-cm cube of a given substance. The unit of resistivity is ohm/centimeter. e. The reciprocal of conductivity. Syn: thermal resistivity.

resistivity method
 * Any electrical exploration method in which current is introduced into the ground by two contact electrodes and potential differences are measured between two or more other electrodes.

resistivity profile
 * a. A geophysical survey using the resistivity method. An assembly of electrodes spaced at a constant distance is moved along profiles, resulting in lateral variations in resistivity being shown. In favorable terrain, the test shows the existence of faults that have thrown strata of different resistivity against each other; similar relationships result in the detection of an anticline, a syncline, or an underground channel.

b. A survey by the resistivity method in which an array of electrodes is moved along profiles to determine lateral variations in resistivity.

resistor
 * A device to provide resistance in an electric circuit, usually to limit the current, dissipate energy, or provide heat.

resoiling
 * The replacement of the original topsoil at an opencast site on completion of operations to allow the growing of crops. See also: surface reinstatement.

resolution
 * a. A measure of the ability of individual components, and of remote-sensing systems, to distinguish detail or to define closely spaced targets.

b. The minimum size of a feature that can be detected. See also: resolving power. c. The separation of a vector into its components. d. The sharpness with which the images of two closely adjacent spectrum lines, etc., may be distinguished. e. In gravity or magnetic prospecting, the indication in some measured quantity, such as the vertical component of gravity, of the presence of two or more close but separate disturbing bodies. f. In seismic prospecting, the ability to indicate separately two closely adjacent interfaces. g. The ability of an optical or radiation system to separate closely related forms or entities; also, the degree to which they can be discriminated.

resolution limit
 * In gravity and magnetic prospecting, the separation of two disturbing bodies at which some obvious indication in a measured quantity of the presence of two separate bodies ceases to be visible.

resolved-time method
 * A seismic reflection technique that involves the plotting of reflections in time and the representation of horizontal distances along the section in equivalent time units (obtained by dividing the true horizontal distance by the sub-weathering velocity as determined from first-arrival times). Once this transformation of the coordinate system is made, migration is accomplished by swinging arcs of reflection times from successive shot points and drawing lines which are tangent to the respective arcs for the same events from adjacent shot points. For the final mapping of migrated horizons in depth, the times are recorded directly beneath the shot points. These times are converted to depths by using the best available velocity information.

resolving power
 * In optical viewing, the minimum distance possible between two separately distinguishable objects.

resonance
 * a. A term denoting a variety of phenomena characterized by the abnormally large response of a system having a natural vibration period to a stimulus of the same, or nearly the same, frequency.

b. A buildup of amplitude in a physical system when the frequency of an applied oscillatory force is close to the natural frequency of the system.

resonance screen
 * A high-speed vibrating screen in which the applied force has a frequency equal to the natural frequency of the suspended mass. In its basic form, the vibrating frame of the resonance screen is a mass oscillating between two compression springs, that alternately store and return this energy.

resonant frequency drilling
 * Drilling that utilizes longitudinal vibration corresponding to the resonant frequency of the drill string in order to "fluidize" the sediments being sampled, thereby achieving efficient penetration.

resorption border
 * A border of secondary minerals, produced by partial resorption and recrystallization, surrounding an original crystal constituent of a rock. Syn: corrosion border.

resource
 * A concentration of naturally occurring solid, liquid, or gaseous material in or on the Earth's crust in such form and amount that economic extraction of a commodity from the concentration is currently or potentially feasible.

resource characterization
 * The determination of the shape, size, quality, quantity, and variability of the geologic entity and the limits of variable geologic features, so as to provide the information for synthesis of commonly subtle features into an accurate, predictive description of the resource environment.

respirable-size particulate
 * Particulates in a size range that permits them to penetrate deep into the lungs upon inhalation.

respirator
 * a. A device (such as a gas mask) for protecting the respiratory tract (against irritating and poisonous gases, fumes, smoke, dusts) with or without equipment supplying oxygen or air.

b. A device for maintaining artificial respiration. c. The mining-type respirator is a fitting that covers the nose and mouth to prevent the wearer inhaling excessive quantities of dust. Tunnel miners and workers at sinter plants and blast furnaces are issued respirators for use where danger is known to exist. See also: filter-type respirator; mask. d. A device worn over the mouth or nose for protecting the respiratory tract from noxious gases or dust.

respirator protection factor
 * a. A measure of the degree of protection provided by a respirator to the wearer.

b. The ratio of the ambient concentration of an airborne substance to the concentration of the substance inside the respirator at the breathing zone of the wearer, a measure of the degree of protection provided by a respirator to the wearer.

respiratory cycle
 * One complete breath--an inspiration followed by an expiration, including any pause that may occur between the movements.

resplendent
 * Referring to a degree of luster that reflects with brilliancy and gives well defined images; e.g., hematite and cassiterite.

rest magma
 * See: residual liquid.

restoration
 * a. Restoring the disturbed land to the conditions which existed at the site before any disturbance occurred.

b. The process of gaining or recovering land, bringing it into a condition for cultivation or other use. c. Response to any disturbances to the Earth and its environment caused by mining activity. d. Returning the disturbed site "to a form and productivity in conformity with a prior use plan." e. The Surface Mining Control and Reclamation Act of 1977 (SMCRA) states that, among other provisions, reclamation must "restore the land affected to a condition capable of supporting the uses which it was capable of supporting prior to any mining, or higher or better uses."

restore circulation
 * The action taken to fill or seal the cracks or openings through which drill fluid is escaping from the borehole into the rocks forming the walls of the borehole and by which the drill fluid is made to return to and overflow the collar of the borehole.

restrained cable plug and socket
 * a. A flameproof restrained plug and socket incorporates an interlock to ensure that the power connections are dead when they are separated or until they make contact; the design is such that the enclosure is flameproof at all times when there is contact between the pins and tubes.

b. A plug and socket designed to be held together by an operating bolt, or screwed union ring, or other equivalent device, the use of which enables the plug to be readily inserted or withdrawn.

restrained plug and socket
 * These are used when the cable is removed from a machine or apparatus frequently. The most common type is the 100-amp British Standard plug and socket, and it is employed to connect the trailing cable to a coal cutter or face conveyor. The gland of the plug is arranged to grip the sheath of the cable and to make connection with the screen and earth core. Power and pilot conductors are connected to the appropriate contact tubes, which make connection with corresponding pins in the socket portion.

restricted earth fault protection
 * As used in mining, a system of earth fault protection in which the fault current is limited, without requiring the use of sensitive earth fault protection.

restricted resources
 * That part of any resource category that is restricted from extraction by laws or regulations, but otherwise meets all the requirements of reserves.

rests
 * The arrangement at the top and bottom of a shaft, or intermediate levels, for supporting the shaft cage while changing the tubs or cars. See also: chair; catch; wing.

resue
 * a. To mine or strip sufficient barren rock to expose a narrow but rich vein, which is then extracted in a clean condition.

b. To open up a stope, not in the vein but in the wall rock. See also: resuing. c. In lode mining, separate removal of undercut barren rock immediately below a lode or vein too narrow for human entry. Following this, the lode is mined and separately removed. Used when the lode is less than 30 in (76 cm) wide.

resuing
 * a. A method of stoping wherein the wall rock on one side of the vein is removed before the ore is broken. Employed on narrow veins, less than 30 in (76 cm), and yields cleaner ore than when wall and ore are broken together.

b. A method of stoping in which the ore is broken down first and then the waste or vice versa; usually the one which breaks easier is blasted first. The broken waste is left in the stope as filling, and the ore is broken down on flooring laid on the fill to prevent admixture of ore and waste. Resuing is applicable where the ore is not frozen to the walls and works best if there is considerable difference between the hardness of the ore and of the wall rocks.

resurgence
 * See: emergence.

retaining mesh
 * In sieving or screening, that mesh at which division is made between oversize (arrested on screen) and undersize (passing through meshes).

retaining ring
 * a. In drilling, a shoulder inside a reaming shell that prevents entry of the core lifter into the core barrel.

b. A term sometimes incorrectly applied to a core lifter.

retaining screen
 * The screen that has retained the particles.

retaining structure
 * A temporary or permanent structure used for holding dredged material on a limited basis, not to be confused with a confined disposal facility.

retardation
 * In crystal optics, the amount by which the slow wave falls behind the fast wave during passage through an anisotropic crystal plate. Retardation depends on plate thickness and the difference in refractive indices of its two principal directions.

retarding conveyor
 * a. A chain-type conveyor used on steeply inclined faces, where the problem is not so much to move the coal but rather to restrain its movement downhill. It consists of link chains carrying discs 6 to 8 in (15 to 20 cm) in diameter at every yard (0.9 m). The endless chain runs in an open semicircular trough, and the coal is lowered to the discharge end. The chain returns uphill, in an enclosed tube, to the driving unit at the top end. Its capacity is about 100 tons per hour.

b. Any type of conveyor used to retard the rate of movement of bulk materials, packages, or objects, where the slope is such that the conveyed material tends to propel the conveying medium. See also: declining conveyor.

retentivity
 * The capacity of a material to retain a portion of the magnetic field set up in it after the magnetizing force has been removed.

retgersite
 * A tetragonal mineral, NiSO (sub 4) .6H (sub 2) O ; dimorphous with nickelhexahydrite; blue green; associated with morenosite, the septehydrate.

Retger's salt
 * Thallium silver nitrate that melts to a yellow liquid at 75 degrees C having a density of 4.6 g/cm (super 3) ; can be diluted and used as a heavy liquid for mineral separation.

reticular
 * See: reticulate.

reticulate
 * a. Said of a vein or lode with netlike texture; e.g., stockwork. CF: stockwork.

b. Said of a rock texture in which crystals are partially altered to a secondary mineral, forming a network that encloses remnants of the original mineral. CF: mesh texture. See also: reticulated. Syn: reticular.

reticulated
 * A mineral structure of fibers or columns that cross to resemble a net; e.g., rutile. See also: reticulate.

reticulated veins
 * Veins that cross each other, forming a network. See also: stockwork.

reticulate texture
 * See: mesh texture.

reticule
 * A set of intersecting very fine lines, wires, etc., in the optical focus of an optical instrument. It is also referred to as graticule. See also: collimation line.

reticulite
 * An extremely attenuate pyroclastic rock consisting of glass threads which join a series of points forming a polyhedral space lattice. It is formed from pumice by the collapse of the walls of adjacent vesicles and the retraction of the liquid into threads which form the perimeters of the former polygonal faces. The threads are usually of triangular cross section, indicating chilling, before rounding could take place. Such rock has generally been known by Dana's name, thread-lace scoria. See also: thread-lace scoria.

retiform
 * Netted; reticulate; said of the boundaries of some vein quartz (rare).

retigen
 * Bitumen contained in meteorites. The name indicates that this substance on distillation gives rise to resin, in contrast to kerogen which on distillation gives rise to oil.

retinalite
 * A massive, honey-yellow or greenish variety of serpentine with a waxy or resinous luster.

retinasphalt
 * A light brown resinous substance found in brown coal in Devonshire, England.

retinite
 * A variety of fossil resin found as rodlets secreted in canals or ducts of coal-forming plants.

retinosite
 * A microscopical constituent of torbanite consisting of translucent orange-red discs. CF: gelosite; humosite; matrosite.

retonation wave
 * A wave passing back through burned or burning explosion gases toward the origin, at the rate of a sound wave through gases of like temperature, from a point in the explosion wave, usually of high pressure, to an area of lower pressure.

retort
 * a. A vessel used for the distillation of volatile materials, as in the separation of some metals and the destructive distillation of coal.

b. A long semicylinder, now usually of fireclay or silica, for the manufacture of coal gas. c. See: amalgam retort.

retorting
 * a. Removing the mercury from an amalgam by volatizing it in an iron retort, conducting it away, and condensing it.

b. In the sulfur industry, synonymous with sublimation.

retort pressman
 * A person who operates a hydraulic press in which fireclay retorts, used in smelting zinc ores, are made.

retract
 * The mechanism by which a dipper shovel bucket is pulled back out of the digging.

retractable wedge
 * A type of deflecting wedge that can be retrieved after the deflected drill hole has been completed. Syn: retrievable wedge.

retracting
 * See: crowding.

retreat
 * To work rooms or pillars to finish coal or ore extraction in an area that has been penetrated to its limits by advance work; workings are generally in the opposite direction of advance work and allow the area to be abandoned as finished.

retreating longwall
 * a. First driving haulage road and airways to the boundary of a tract of coal and then mining it in a single face without pillars back toward the shaft.

b. See: longwall retreating.

retreating system
 * a. A method of working a mine that is designed to allow a stope to cave soon after it is worked out, thus relieving the weight on the supports in adjacent stopes.

b. A method of extracting coal or ore by driving a narrow heading to the boundary, then opening out a face and working the deposit backwards towards the shaft, drift, or main entry. See also: longwall retreating. c. A stoping system in which supporting pillars of ore are left while deposit is worked outward from shafts toward the boundary, the pillars being removed (robbed) as the work retreats toward the shaft; the unsupported workings are abandoned and left to cave in. d. A system of robbing pillars in which the line of pillars being robbed retreats or moves from the boundary toward the shaft or mouth of the mine. See also: longwall retreating.

retrievable inner barrel
 * The inner barrel assembly of a wire-line core barrel, designed for removing core from a borehole without pulling the rods.

retrievable wedge
 * See: retractable wedge.

retrieving ring
 * A catch ring on a retractable wedge that engages a lifting device on the deflection barrel or bit, enabling the drill runner to remove a deflecting wedge from a borehole after deflection has been effected.

retrograde metamorphism
 * The mineralogical adjustment of relatively high-grade metamorphic rocks to temperatures lower than those of their initial metamorphism, characteristically inducing hydration and hydrous minerals. Syn: retrogressive metamorphism; diaphthoresis. CF: prograde metamorphism.

retrogressive metamorphism
 * See: retrograde metamorphism.

return
 * a. Any airway in which vapid air flows from the workings to the upcast shaft or fan. See also: intake.

b. Any airway which carries the ventilating air from the face outby and out of the mine. c. Any surface turned back from the face of a principal surface. d. The rate of profit in a process of production per unit of cost.

return air
 * a. Air traveling in a return.

b. Air that has circulated the workings and is flowing towards the main mine fan; vitiated or foul air. c. Air returning to a heater or conditioner from the heated or conditioned space.

return aircourse
 * Portion of ventilation system of mine through which contaminated air is withdrawn and evacuated to surface.

return circulation
 * That portion of a circulated drill fluid flowing from the face of a bit toward the collar of a borehole. CF: return water.

returning charge
 * Charge made per unit of ore or concentrate treated by smelter in custom smelting. In addition to a basic charge that allows for process costs and agreed percentage loss in recovery, extra charges may be specified, or remitted as premiums, in adjustment of variations from the normal makeup of the parcel treated.

returning fluid
 * The water, mud, or other circulated medium reaching the borehole collar after having been circulated past the drill bit.

return-line corrosion tester
 * A tester developed by the U.S. Bureau of Mines for detecting and controlling corrosion in steam-condensate-return lines of large heating plants. This tester determines types and rates of corrosion and can distinguish among various possible causes. It is assembled from ordinary black iron pipe nipples and couplings, the linings are easily machined, and the corroded linings can be analyzed quickly in any laboratory.

return man
 * In anthracite coal mining, one who resets timbers, shovels up falls of slate, rock, or dirt, and keeps in general repair the airways by which mine air returns to the surface.

returns
 * a. The drill fluid and entrained sludge that overflows the collar of a borehole.

b. In seismic reflection prospecting, the signals reflected back to the surface from layer boundaries in the subsurface. c. Also used in geophysical prospecting to register passage of waves caused by detonation of dynamite.

return water
 * Drill fluid that reaches the surface and overflows the borehole collar after it has been circulated downward through the rods and past the drill bit.

retzian
 * An orthorhombic mineral, (Mn,Mg) (sub 2) (Ce,La,Nd)(AsO (sub 4) )(OH) (sub 4) ; speciated on the basis of predominance of cerium, lanthanum, or neodymium; in dolomite cavities in Sweden.

reussin
 * An impure Glauber's salt (mirabilite), found native.

reussinite
 * A resinlike, reddish-brown oxygenated hydrocarbon, soluble in boiling alcohol and in ether. Found in certain coal deposits.

revdanskite
 * An impure, hydrous nickel silicate from Revda (Revdinsk), Ural Mountains, Russia. Also spelled revdinite, revdinskite, rewdinskit, rewdanskite; rewdjanskit, and refdanskite.

revegetation
 * The process of restoring or replacing the botanical species upon an area disturbed by mineral operations. Revegetation is a customary requirement for reclamation of a mineral operation.

reverberate
 * a. To deflect flame or heat, as in a reverberatory furnace.

b. To reduce by reverberated heat; to fuse.

reverberation
 * a. The persistence of sound in an enclosed space as a result of multiple reflections after the sound source has stopped.

b. The sound that persists in an enclosed space, as a result of repeated reflection or scattering, after the source of the sound has stopped.

reverberatory furnace
 * A furnace, with a shallow hearth, usually non-regenerative, having a roof that deflects the flame and radiates heat toward the hearth or the surface of the charge. Firing may be with coal, pulverized coal, oil, or gas. Two of the most important types are the open-hearth steel furnaces and the large reverberatories employed in copper smelting.

reversal
 * A local change of approx. 180 degrees in the direction of the regional dip.

reversal of ventilation
 * In the case of a centrifugal fan, the reversal arrangement may consist of an emergency drift connecting the fan with the downcast shaft. The drift is normally sealed off by airtight doors. In the case of an axial-flow fan, it is only necessary to reverse the rotation of the fan. This arrangement entails a reduction in volume and pressure in the reversed airflow.

reverse bearing
 * In surveying, a sight along the reverse direction of a line; the reciprocal of a given bearing. See also: backsight.

reverse bend
 * To bend a line over a drum or a sheave, and then in the opposite direction over another sheave.

reverse book fashion
 * The manner in which drill core is laid in a core box, starting at the upper-right-hand corner of the box and laying core from right to left in each groove. CF: snake fashion.

reverse circulation
 * The circulation of bit-coolant and cuttings-removal liquids, drilling fluid, mud, air, or gas down the borehole outside the drill rods and upward inside the drill rods. Also called countercurrent; counterflush. See also: circulating fluid.

reverse-circulation core barrel
 * A core barrel designed so that core tends to float within the barrel when the fluid is circulated down the outside of the rods and returned to the surface inside the rods.

reverse classification
 * In jigging, stratification of particles by size with largest uppermost; in streaming, rolling effect of transporting current that arranges particles with smallest nearest feed end.

reverse-current braking
 * A method used in the braking of alternating-current winders. This method absorbs power equal to the energy destroyed and dissipates it in the liquid controller as heat. Two phases of the stator supply are interchanged by bringing back the driver's lever to the off position and then to that for the opposite direction of drum rotation. The amount of braking depends upon the position of the lever, since the lower the resistance in the controller, and therefore in the rotor circuit, the greater the rotor current and the braking torque produced. When the direction of rotation of the stator magnetic field is reversed, the voltage between the stator and the rotor is doubled and the insulation of both must be adequate to prevent breakdown.

reversed
 * See: overturned.

reversed bratticing
 * A method of narrow heading ventilation in coal mines by means of a brattice partition. The air is led to the face along the wide section of the heading and the contaminated air returns from the face along the narrow section. In this way, workers in the heading are placed in relatively clean air.

reversed fault
 * See: reverse fault.

reversed flush boring
 * See: counterboring.

reversed loader
 * A front-end loader mounted on a wheel tractor having the driving wheels in front and steering at the rear.

reverse fault
 * A fault on which the hanging wall appears to have moved upward relative to the footwall. The dip of the fault is usually greater than 45 degrees . There is dip separation but there may or may not be dip slip. CF: normal fault. Partial syn: thrust fault. Syn: reversed fault.

reverse feed
 * To move bit and drill stem backwards away from the borehole bottom while the drill stem is rotated.

reverse-feed gear
 * System of gears in drill swivel head that can be engaged to move the bit and drill stem backwards away from the bottom of the borehole while the drill stem is rotated in a clockwise direction. Syn: backup gear; reverse gear.

reverse gear
 * See: reverse-feed gear.

reverse initiation
 * See: inverse initiation.

reverse laid rope
 * A wire rope with alternate strands right and left lay.

reverse reaming
 * See: ream back.

reversible auxiliary ventilation
 * In this system, a single duct is provided and is normally operated by a blowing fan. After blasting, airflow is reversed and the fumes and dust are exhausted. Ventilation is again reversed to blowing, when the work at the face is resumed. The usual arrangement is to use two fans, one for forcing, one for exhausting, at the mouth of the heading. This arrangement is particularly suited to underground use as it allows clean air to be drawn from, and contaminated air to be discharged to, separate points in the main airways. See also: auxiliary ventilation; two-fan auxiliary ventilation.

reversible endless-rope system
 * A haulage system in which a single rope is used passing around a surge wheel. A single track may be used or, if more than one train is hauled, a single track with passbys, or a three-rail system with passbys, that eliminates facing points, may be used. The system may be operated at higher speeds than normal endless systems since the trains are attached and detached from a rope at rest; it has been used for the haulage of workers at speeds up to 12 mph. Extra rope must be spliced onto the rope, and the return wheel moved forward, when the system is extended.

reversible pick
 * See: double-ended pick.

reversible transducer
 * See: bilateral transducer.

reversing clutch
 * A forward-and-reversing transmission that is shifted by a pair of friction clutches.

reversing doors
 * The system of doors or shutters on or near a surface radial-flow fan for reversing the direction of the air passing through a mine.

reversing machine
 * A molding machine having a flask or flasks that may be turned over for ramming the sand.

reversing mill
 * A type of rolling mill in which the stock being mechanically worked by rolling passes backwards and forwards between the same pair of rolls, which are reversed between each pass. See also: continuous mill; three-high mill.

reversing shaft
 * A shaft whose direction of rotation can be reversed by the use of clutches or brakes.

reversing thermometer
 * A mercury-in-glass thermometer used to measure temperatures of the sea at depth. The temperature is recorded when the thermometer is inverted; and the recording is maintained until it is once again upright. A protected thermometer and an unprotected thermometer are usually used as a pair, attached to a Nansen bottle.

revetment
 * a. A facing, sheathing, or retaining wall of masonry or other materials for protecting a mass or bank of earth, etc., as in fortifications and riverbanks.

b. A wall sloped back sharply from its base.

revolution
 * An obsolete term for a time of profound orogeny and other crustal movements, on a continentwide or even worldwide scale, the assumption being that such revolutions produced abrupt changes in geography, climate, and environment. See: orogeny.

revolving screen
 * A screen consisting of a cylindrical (sometimes conical) screening surface mounted on a revolving frame for sizing coarse material; it is still common in gravel-washing, coal-washing, and stone-treating plants, but is not widely used in ore dressing. See also: trommel; trommel screen.

revolving shovel
 * A digging machine that has the machinery deck and attachment on a vertical pivot, so that it can swing independently of its base.

revolving washing screens
 * The rotary washing screen is cylindrical in shape and made of three sections--a scrubber, a sand jacket, and a gravel-screening section--mounted on a steel frame.

rewash
 * To re-treat a product in the same or in another washer.

rewash box
 * A washbox to which the product (or a portion thereof) of a previous washing operation is fed for additional treatment.

rewdanskite
 * See: revdanskite.

reworked
 * Said of components derived from an older sedimentary formation and incorporated in a younger one.

Reynolds number
 * A numerical quantity used as an index to characterize the type of flow in a hydraulic structure in which resistance to motion depends on the viscosity of the liquid in conjunction with the resisting force of inertia. It is the ratio of inertia forces to viscous forces, and is equal to the product of a characteristic velocity of the system (e.g., the mean, surface, or maximum velocity) and a characteristic linear dimension, such as diameter or depth, divided by the kinematic viscosity of the liquid; all expressed in consistent units in order that the combinations will be dimensionless. The number is chiefly applicable to closed systems of flow, such as pipes or conduits where there is free water surface, or to bodies fully immersed in the fluid so the free surface need not be considered.

Rf value
 * In paper-strip chromatography, ratio of distance moved by component in solution under test to that of transporting solvent.

rhabdite
 * See: schreibersite.

rhabdomancy
 * A form of dowsing using a rod or twig. CF: dowsing.

rhabdophane
 * a. A hexagonal mineral, (Ce,La,Nd)PO (sub 4) .H (sub 2) O ; speciated on the basis of predominance of cerium, lanthanum, or neodymium; Also spelled rhabdophanite.

b. The mineral group brockite, grayite, ningyoite, rhabdophane-(Ce), rhabdophane-(La), rhabdophane-(Nd), and tristramite.

rheid
 * a. A substance below its melting point that deforms by viscous flow during the time of applied stress at an order of magnitude at least three times that of the elastic deformation under similar conditions.

b. A body of rock showing flow structure.

rheid folding
 * Folding accompanied by slippage along shear planes at an angle to the bedding or older foliation.

rheidity
 * The capacity of material to flow within the earth.

Rhenania furnace
 * A combination of the Hasenclever and O'Hara furnaces, with four hearths, and with a combination flue under the lowest hearth and one over the upper hearth. It has mechanical rabbles.

Rhenish furnace
 * A zinc distillation furnace that is a modified type of the Silesian furnace.

rhenium
 * A rare, silvery-white metal. Symbol, Re. Occurs in very small quantities in platinum ores and in columbite, gadolinite, and molybdenite. Used for filaments for mass spectrographs and ion gages; for thermocouples and photoflash lamps.

Rheolaveur washer
 * A washer wherein raw coal and water is fed into the head of an inclined trough equipped with openings in the bottom for the discharge of rejects. There are three types of Rheolaveurs used in coal washing: (1) the sealed discharge type for coarse sizes, from which the reject falls against an upward current of water and is removed by an automatic gate that controls the feed to a drowned elevator; (2) a system of two, three, or four superimposed troughs for washing fine coal below about 1/2 in (1/3 cm). The troughs are equipped with several bottom discharge devices. The separation of the heavy shale from coal and middlings takes place progressively until finally the pure shale is discharged from the lowest trough, and (3) a system for washing slurry consisting usually of two troughs one above the other and equipped with a number of Rheo boxes of the open discharge type but designed to minimize the loss of coal with the fine shale.

rheology
 * Study of the flowage of materials, particularly plastic flow of solids and flow of non-Newtonian liquids.

rheomorphism
 * The process by which a rock becomes mobile and deforms viscously as a result of at least partial fusion, commonly accomplished, if not promoted, by addition of new material by diffusion.

rheostat
 * a. An instrument for testing blasting machines by inserting definite resistance equal to a known number of electric blasting caps of a standard-length wire, using one electric blasting cap as an indicator.

b. An instrument by which a variable or an adjustable resistance may be introduced into a circuit to regulate the strength of a current, as in the field coils of a motor or a generator.

rheostat rope
 * A small rope consisting of 8 strands of 7 wires each.

rhinestone
 * a. Quartz and other material cut to imitate diamond.

b. Glass backed with a thin leaf of metallic foil to simulate a diamond. c. Originally a syn. of quartz crystal. d. Cut colored glass.

rhodesite
 * An orthorhombic mineral, (Ca,Na (sub 2) ,K (sub 2) ) (sub 8) Si (sub 16) O (sub 40) .11H (sub 2) O ; fibrous; resembles zeolites; at Bultfontein Mine, Kimberley, South Africa. See also: mountainite.

rhodite
 * See: rhodium gold.

rhodium
 * a. An element of the platinum group, Symbol: Rh.

b. An isometric mineral, RhPt.

rhodium gold
 * Native gold alloyed with rhodium.

rhodochrome
 * Chromian clinochlore, formerly called kaemmererite.

rhodochrosite
 * A trigonal mineral, MnCO (sub 3) ; calcite group, with Mn replaced by Fe toward siderite, Ca toward calcite, Mg, Zn, Co, and Cd; rhombohedral cleavage; in hydrothermal veins, residual manganese deposits, and pegmatites; a minor source of manganese. Syn: manganese spar. See also: dialogite; raspberry spar.

rhodolite
 * A pale pink, rose, or purple to violet variety of pyrope garnet having good transparency; may be of gem quality.

rhodonite
 * metasomatic manganese ore deposits; an ornamental stone, esp. in Russia. Syn: manganese silicate; manganese spar. See also: red manganese.

rhodotilite
 * See: inesite.

rholites
 * A word employed by Wadsworth to designate smelting materials or fluxes.

rhomb
 * See: rhombus; rhombohedron.

rhombarsenite
 * See: claudetite.

rhombenglimmer
 * See: biotite.

rhombic
 * See: rhombus; orthorhombic.

rhombic dodecahedron
 * The isometric form hh0 having twelve faces in the shape of a rhombus; e.g., garnet. CF: pyritohedron.

rhombic mica
 * See: phlogopite.

rhombic quartz
 * An old name for feldspar.

rhombic system
 * a. In crystallography, same as the orthorhombic system. Syn: orthorhombic system.

b. A former name for the orthorhombic system.

rhomboclase
 * An orthorhombic mineral, HFe(SO (sub 4) ) (sub 2) .4H (sub 2) O ; forms colorless to gray rhombic plates; in Slovakia.

rhombohedral division
 * In assigning point groups to six crystal systems, those members of the hexagonal system that may be assigned rhombohedral crystallographic axes a (sub r) belong to the rhombohedral division of the hexagonal system. They have a unique triad, but not all point groups with a unique triad may be assigned rhombohedral axes; hence, not all trigonal point groups are rhombohedral. CF: trigonal; trigonal system.

rhombohedral iron ore
 * See: siderite.

rhombohedral system
 * a. Same as the hexagonal system, except that the forms are referred to three axes parallel to the faces of the fundamental rhombohedron instead of to the usual four axes.

b. The trigonal division of the hexagonal system, the forms being referred to the same three axes as above. Neither usage has been generally accepted.

rhombohedron
 * A parallelepiped with each face a rhombus. Dolomite crystallizes as rhombohedra, and members of the calcite group cleave as rhombohedra. Adj. rhombohedral.

rhomboid
 * A parallelogram that does not have any right angles, and one pair of opposite sides differ in length from the other pair of opposite sides.

rhomb spar
 * See: dolomite.

rhombus
 * A parallelogram that does not have any right angles, but the sides are all equal in length.

rhoenite
 * A triclinic mineral, Ca (sub 2) (Fe,Mg,Ti) (sub 6) (Si,Al) (sub 6) O (sub 20) ; aenigmatite group; in silica-undersaturated mafic to intermediate rocks commonly as an alteration product of amphiboles; in Germany and the Czech Republic.

rhums
 * Scot. Bituminous shale.

rhyacolite
 * See: sanidine.

rhyodacite
 * The extrusive equivalent of granodiorite. The principal minerals, sodic plagioclase, sanidine, quartz, and biotite or hornblende, commonly occur as phenocrysts in a finely crystalline groundmass of alkali feldspar and quartz. Accessory minerals are apatite and magnetite, and occasionally augite.

rhyolite
 * A group of extrusive igneous rocks, typically porphyritic and commonly exhibiting flow texture, with phenocrysts of quartz and alkali feldspar in a glassy to cryptocrystalline groundmass; also, any rock in that group; the extrusive equivalent of granite. Rhyolite grades into rhyodacite with decreasing alkali feldspar content and into trachyte with a decrease in quartz. The term was coined in 1860 by Baron von Richthofen (grandfather of the World War I aviator). Etymol: Greek rhyo-, from rhyax, stream of lava. See also: liparite. CF: quartz porphyry.

rhyolite glass
 * Obsidian.

rhyolite-porphyry
 * A rhyolite in which some grains or crystals are visibly larger than others.

rhythmic crystallization
 * A phenomenon, observed in igneous rocks, in which different minerals crystallize in concentric layers, giving rise to orbicular structure.

rhythmic driving
 * In this type driving, the drilling, loading, and blasting are carried out in one shift and the mucking and transportation in the following one. This enables every worker to specialize in his or her tasks and machines, which in a highly mechanized job is a necessary condition for making the best use of expensive equipment. It also reduces or eliminates the loss of time for ventilation; in rhythmic driving it is carried out between two shifts.

rhythmic sedimentation
 * A regular interbanding of two or more types of sediment or sedimentary rocks due to a regular change in the conditions of sedimentation, such as alternation of wet and dry periods. See also: varved clay.

rhythmite
 * The couplet of distinct types of sedimentary rock, or the graded sequence of sediments, that form a unit bed or lamina in rhythmically bedded deposits. It implies no limit as to thickness of bed, lamina, or complexity, but the term should exclude groups of beds such as cyclothems and carries no time or seasonal connotation. CF: cyclothem; varve.

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