Silicate of calcite, aluminum, and iron
Color: Pistachio green to
yellowish green to black
Luster: Vitreous, pearly, resinous
Specific Gravity: 3.38-3.39
Cleavage: Perfect, one direction
Habit: Crystals are short to long
prismatic, tabular, and acicular.
Aggregates are massive, coarse to fine
granular, and fibrous.
Epidote is a colorful mineral of
metamorphic origin that is relatively
common in some parts of California. Its
characteristic pistachio green color,
hardness (harder than a knife blade),
and relatively high specific gravity are
usually sufficient for identification of
this mineral. Most commonly it is found
in compact masses of tiny grains, the
latter too small to be individually
distinguished without the aid of a hand
lens or microscope. But in places it is
found in coarsely crystalline aggregates
so that the elongate, vitreous crystals
can be easily distinguished. It is most
commonly associated with white quartz
and calcite and reddish- brown garnet.
Epidote is one of the characteristic
minerals formed when limestone is
metamorphosed by high temperatures and
fluids emanating from granitic magma.
Thus it is most abundant in areas where
granitic rocks are exposed. It is also a
constituent of some schist, but is not
particularly apparent in these rocks.
Epidote has no commercial value, but is
significant to the geologist in that
it's presence near granite commonly
indicates metamorphic zones in which
tungsten and molybdenum ores may be
found. First described in 1801 and named
from the Greek word for increase because
the prism base has one side longer than
in Which this Mineral is Found
San Luis Obispo
Specimen Description: Epidote, 8.5 cm
wide, Calaveras County. California
Division of Mines and Geology Library.
Photographer: Max Flanery, CGS.