Rocks older than the Cambrian age. Name refers to the great shield-shaped
areas of ancient mineral-bearing rocks. These ancient rocks occur in many
parts of the world. Cumming, 1
Grouting the strata to control ground water prior to the start of
construction or excavation, such as shaft sinking. Precementation has been
used in South Africa to depths of 4,000 ft ( 1,200 m) and considerable
savings have resulted. See also:cementation sinking
Descriptive of the finest variety of a gem or mineral. Syn:oriental;
precious stone.
Brilliantly purple almandine.
Any of several relatively scarce and valuable metals, such as gold,
silver, and the platinum-group metals. ASM, 1
See:peridot
A gem variety of opal that exhibits a brilliant play of delicate colors by
diffraction of light from close-packed 150- to 300-mm spheres of
cristobalite-tridymite. The color of the bulk material may be black or
white. CF:common opal
A pale or dark oil-green, massive, translucent serpentine. Dana, 1
See:gemstone
a. Genuine topaz as distinguished from topaz-colored quartz (jewelers'
topaz).
b. An incorrect term for yellow to brown sapphire.
Dark-colored gem variety of tourmaline.
Any agent, as a reagent, that when added or applied to a solution causes a
precipitate of one or more of its constituents. Standard, 2
a. The operation, act, or process of adding a chemical or chemicals to an
aqueous solution to react with a dissolved material in the solution and
remove the resulting new solid matter by settling.
b. The solids resulting from the precipitation process.
Sulfur precipitated from calcium polysulfide solutions by hydrochloric
acid and washed to remove all calcium chloride.
a. The process of separating mineral constituents from a solution; e.g.,
by evaporation (such as halite or anhydrite) or by cooling of magma (to
form an igneous rock).
b. Exsolution.
c. Water that falls to the surface from the atmosphere as rain, snow,
hail, or sleet. It is measured as a liquid-water equivalent regardless of
the form in which it fell. AGI
Metal-rich water, as it moves away from the source of the metal,
ordinarily comes into an environment where changing conditions of some
kind cause precipitation of part or all of the metal from the water.
Precipitation barriers account for the more than normal decay of
hydrochemical anomalies than can be accounted for by simple dilution. They
characteristically occur in spring and seepage areas where groundwaters
coming to the surface encounter an environment of increased availability
of oxygen, sunlight, and organic activity. Hawkes, 2
Hardening caused by the precipitation of a constituent from a
supersaturated solid solution. See also:aging; hardening.
ASM, 1
Artificial aging in which a constituent precipitates from a supersaturated
solid solution. See also:artificial aging; progressive aging.
ASM, 1
a. The manipulation of physical and/or chemical properties of a solution
to cause one of the constituents of that solution to become insoluble.
b. The treatment of lead ores by direct fusion with metallic iron or slag,
or ore rich in iron; performed generally in a shaft furnace, rarely in a
reverberatory. It is often combined with the roasting and reduction
process. See also:iron-reduction process
In beneficiation, smelting, and refining, a person who (1) tends zinc
boxes in which gold or silver that has been dissolved in a cyanide
solution is precipitated; and (2) precipitates gold from cyanide solution,
except that the cyanide solution is agitated with zinc dust in a mixing
cone and precipitate, then turned into a filter press where the
precipitate is recovered prior to the drying and refining to secure the
gold. DOT
The degree of agreement or uniformity of repeated measurements of a
quantity; the degree of refinement in the performance of an operation or
in the statement of a result. It is exemplified by the number of decimal
places to which a computation is carried and a result stated. Precision
relates to the quality of the operation by which a result is obtained, as
distinguished from accuracy, but it is of no significance unless accuracy
is also obtained. AGI