A rectifier that changes single-phase alternating current into pulsating
unidirectional current, utilizing only one-half of each cycle.
Coal Age, 1
Half the width of a simple anomaly (esp. a gravity or magnetic anomaly) at
the point of half its maximum value. For simple models the maximum depth
at which the body causing the anomaly can lie can be calculated from the
half width. AGI
A fluoride, chloride, bromide, or iodide.
Miniature pneumatic flotation cell, operated by hand. Widely used in ore
testing, for examination of small samples under closely controllable
conditions of flotation. Pryor, 3
An isometric mineral, 4[NaCl] ; cubic cleavage; soft; salty tasting; forms
disseminated grains or crystals in sedimentary rocks, or aggregates of
large cubic crystals; granular to massive, the latter as extensive
sedimentary beds ranging in thickness from less than 1 mm to more than 50
m, also in convoluted masses called salt domes; a typical constituent of
playa lake deposits in arid regions. Syn:rock salt; common salt; salt.
Composed partly or wholly of halite; esp. said of a sedimentary rock
containing halite as cementing material, such as halitic sandstone.
AGI
Sw. A dense, compact, metamorphic rock consisting of microscopic quartz
and feldspar crystals, with occasional phenocrysts and sometimes
hornblende, chlorite, magnetite, and hematite. It is associated with
gneisses, but is of obscure origin. See also:porcellanite
A table of the Wilfley type, except that the tops of the riffles are in
the same plane as the cleaning planes and the riffles are sloped toward
the wash-water side. Liddell
A tunneling shield of Hungarian design, successfully employed for
tunneling at Dortmund and under the Danube. It is valuable for working in
very soft ground. It incorporates a mechanical excavator and does not
entail the use of timbering to protect the miners. Hammond
a. A monoclinic mineral, 2[Al4 Si4 (OH)8 O10 ];
kaolinite-serpentine group; made up of slender tubes as shown by
electron microscopy; a gangue mineral in veins. Syn:metahalloysite
b. Used as a group name to include natural "halloysite minerals" with
different levels of hydration, as well as those formed artificially.
See also:alum salt
The first commercially successful method for manufacturing aluminum; the
purified oxide is dissolved in fused cryolite and then electrolyzed.
Syn:Heroult process
A tapered concave metal plug or wedge that can be set in a drill hole at a
predetermined depth and bearing to deflect or straighten an off-course
borehole. See also:wedge
a. A circular or crescentic distribution pattern about the source or
origin of a mineral, ore, mineral association, or petrographic feature. It
is encountered principally in magnetic and geochemical surveys. Some halos
are primary, formed either at the same time as the host rock or at the
same time as associated mineral deposits, and some are secondary, formed
by surficial alteration of the associated mineral deposit. Syn:aureole
CF:dispersion pattern
b. Discoloration of a mineral, viewed in thin section, in the form of a
ring. Most halos of this sort are caused by radiation damage by alpha
particles emitted from uranium- and thorium-bearing mineral inclusions.
A steep ascendent of salinity. This has an effect on refraction of sound
waves, since sound velocity increases with increasing salinity. Hy
See:salt tectonics
a. A monoclinic mineral, 4[Fe2+ Al2 (SO4 )4
.22H2 O] ; forms a series with pickeringite in which magnesium
replaces ferrous iron; soft; a weathering product of pyritic rocks in
mines; also in arid regions and around fumaroles.
b. The mineral group apjohnite, bilinite, dietrichite, halotrichite,
pickeringite, and redingtonite. Syn:feather alum; iron alum.
A mixture of yellow prussiate of potash, niter, and charcoal used as an
explosive. Fay
An orthorhombic mineral, 8[Be2 (BO3 )(OH)] ; in alkali
pegmatites and in placers.
An extensive, nearly level, upland desert surface that is either bare
bedrock or bedrock thinly veneered by pebbles, smoothly scoured and
polished and generally swept clear of sand and dust by wind action; a rock
desert of the plateaus, esp. in the Sahara. The term is also used in other
regions, as in Western Australia and the Gobi Desert. Etymol: Arabic,
hammadah. AGI
a. Term for drive hammer, a heavy sleeve-shaped weight used for driving
drill pipe or casing into overburden or soft rock. Long
b. To pound or drive with pilehammerlike blows delivered by a drive
hammer. Long
An impact type of breaker consisting of a number of swinging bars or steel
hammers hinged to a horizontal shaft that rotates at high speed.
Nelson