Epidote is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Monoclinicly structured gems are made of calcium aluminum hydrosilicate, their full chemical compound being Ca2(Al,Fe)(SiO4)3.

Epidote is widespread, forms a continuous series of minerals, ending with clinozoisite, which contains no iron.

It occurs as crystals elongated and often striated parallel to length, and also as massive, fibrous, or granular habits.

Epidote has a yellow-green color, ranges from yellowish-greenish to greenish-black. It has vitreous luster, and is transparent to nearly opaque. It has one perfect basal cleavage parallel to the length of crystals.

It fuses with swelling to a black, magnetic glass. It is infusible.

It is common in medium- or low-grade metamorphic rocks which have formed either from calcareous or basic rocks, associated with garnet, diopside, idocrase, and calcite in impure limestones. It occurs in "saussurite," the alteration product of feldspar, and is formed from the alteration of hornblende.

Varieties include "Withamite," a pink, manganese-bearing epidote found in vesicles and veins in andesite, mostly from Italy and metabasites in Cyprus; "Pumpellyite," a widely-distributed, hydrous, epidote-like material, found in low-grade metamorphosed tuffs, and also in the vesicles of ancient lavas; "Pistacite," a pistachio-green variety; "Piemontite," opaque, cherry-red variety, contains manganese, from Piemont (Italy); "Tawmawite," or "Chrome epidote," (mistakenly called "chrome jade," a chromium-bearing variety found in Burma, also in Finland; "Delphinite," yellowish-green from France, sometimes called "oisanite" or "thallite;" "Clinozoisite," a light-green to green-brown variety which is iron-free.

Good to splendid crystals are found in Untersulzbachtal (Austria), "arendalite" from Arendal (Norway), (Isere) France, the Naziamsky mountains (Urals, Soviet Republics). Cuttable qualities are also found in Mexico, Mozambique, California (USA)

Misleading terms include "Burma epidote," which is actually jade-albite from Myanmar (Burma);

It may be mistaken for tourmaline, which lacks cleavage and has a triangular or hexagonal cross-section.

The specific gravity [?] for Epidote is 3.4, it's refractive index [?] is 1.74-1.78, and it's double refraction [?] is 0.035.

History

Epidote is formed by hydrothermal alteration of plagioclase in gabbros, and in vesicles in basic lava flows. It derives its name from the Greek word "epidosis" meaning "addition."

Industrial Usages

Epidote is occasionally used in jewellery, but is mainly of interest to scientists and collectors.

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Tags

epidotemineralclinozoisiteyellow greenwithamitepumpellyitepistacitepiemontitetawmawitechrome epidotedelphiniteoisanitearendaliteepidosiscalcium aluminum hydrosilicate

Terms

Double Refraction or dr is the ability of a mineral to separate a refracted ray of light into 2 rays. If held over an image or text it will display the object 2x its original size.

Mohs Scale of Mineral Hardness is the standard used to categorize a mineral's ability to resist scratching. It gets its name from Friedrich Mohs, the German geologist who first created the scale.

RI or Refractive Index defines light's ability to move through the mineral or in a general sense, any material.

SG or Specific Gravity is the ratio of the weight of any substance to that of pure water at temperature of 3.98°C(39.2°F) and standard atmospheric pressure. This is important to note when actively seeking these minerals in the wild. Minerals with a higher SG will settle below material with a lower sg over time.