DEFINITION OF HEAVY MINERALS

Detrital sedimentary grains that have a

higher specific gravity than the standard mineral in a sandstone,

or other detrital sedimentary rock. Most heavy miner-

als have a density above 2.9 grams per cubic centimeter and

form a minor component of the sediment or sedimentary

rock, with common minerals including magnetite, ilmenite,

chromite, sphene, zircon, rutile, kyanite, garnet, tourmaline,

apatite, olivine, hornblende, and biotite. Less commonly, ore

minerals such as gold may occur as detrital heavy mineral

concentrates in some deposits.

Heavy minerals are generally eroded from igneous and

metamorphic rock terrains and resist weathering more than

feldspar, eventually becoming concentrated as detrital grains

in sands and other clastic deposits. Certain types of heavy

minerals generally form only in specific types of rocks; for

instance garnet forms in metamorphic rocks, and chromite

forms in ultramafic rocks. Using such relationships, it is often

possible to learn much about the source terrane of the sediment

or sedimentary rock by examining the heavy mineral

concentrates from that deposit.

See also SEDIMENTARY ROCKS.

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