Aragonite
A carbonate mineral, the stable form of calcium carbonate
(CaCO3) at high pressures.
It is somewhat harder and has a slightly higher specific
gravity than calcite. Aragonite is found in recent deposits formed at low
temperatures near the surface of the earth, as in caves as stalactites, with
ore minerals, in serpentine and other basic (see acid and basic rocks) rocks,
and in sediments. Aragonite is the mineral normally found in pearls, and it
occurs in some animal shells. It is polymorphous (same chemical formula but
different crystal structure) with calcite and vaterite, and, with geologic
time, changes to calcite even under normal conditions.
Source: Britannica encyclopedia
