peridotiteArticle Free Pass peridotite, a coarse-grained, dark-
coloured, heavy, intrusive igneous rock that contains at least
10 percent olivine, other iron- and magnesia-rich minerals
(generally pyroxenes), and not more than 10 percent feldspar. It
occurs in four main geologic environments: (1) interlayered with
iron-, lime-, and magnesia-rich rocks in the lower parts of
tabular-layered igneous complexes or masses; (2) in alpine-type
mountain belts as irregular, olivine-rich masses, with or
without related gabbro; (3) in volcanic pipes (funnels, more or
less oval in cross section, that become narrower with increasing
depth) as kimberlite; and (4) as dikes (tabular bodies injected
in fissures) and irregular masses with rocks exceptionally rich
in potash and soda. The layered complexes are believed to have
been formed in place by selective crystallization and crystal
settling from a previously intruded fluid or magma; the
remaining types seem to have ranged from fluid magmas to
semisolid crystal mushes at the