Epidote

Epidote

Epidote
 

Composition: Silicate of calcite, aluminum, and iron  (HCa2(Al,Fe)3Si3O13O)

Synonyms/Varieties:
Pistacite
Tawmawite

Physical Properties:
Color: Pistachio green to yellowish green to black
Streak: White-gray
Luster: Vitreous, pearly, resinous
Hardness: 6.5
Tenacity: Brittle
Specific Gravity: 3.38-3.39
Cleavage: Perfect, one direction

Crystallography:
System: Monoclinic
Twinning: Common
Habit: Crystals are short to long prismatic, tabular, and acicular. Aggregates are massive, coarse to fine granular, and fibrous.

General Information:
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 another.

California Counties in Which this Mineral is Found
 

Butte
Calaveras
Colusa
El Dorado
Fresno
Humboldt
Imperial
Inyo
Kern
Lassen
Los Angeles
Madera
Marin
Mariposa
Mendocino
Mono
Nevada
Plumas
Riverside
San Bernardino
San Diego
San Luis Obispo
Santa Barbara
Siskiyou
Sonoma
Trinity
Tulare
Tuolumne
 

Information on Specimen Photo:
Specimen Description: Epidote, 8.5 cm wide, Calaveras County. California Division of Mines and Geology Library.
Photographer: Max Flanery, CGS.