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Epidote

Unknown18.01 | , ,
Epidote is fairly dense, fragile with distinct cleavage and is rarely cut as a gemstone. Epidote crystals are yellow, green, or dark brown columnar prisms, with faces finely striated parallel to the crystal's length. Pleochroism is strong, showing either yellow, green, or brown. Rock composed mainly of epidote may be polished or tumbled and sold as unakite.
 
Dark green crystals occur in the Austrian and French Alps. Epidote is also found in the former USSR, Italy, the island of Elba (Italy), Mozambique and Mexico.





Epidote Properties

Chemical Composition: 
Calcium Aluminium Silicate with Iron - Ca2(Fe,Al)3(SiO4)3(OH)
Classification / Type: 
The epidote group is an isomorphous group comprising the following minerals:
  1. Zoisite
  2. Clinozoisite
  3. Epidote
  4. Piedmontite
  5. Hancockite
  6. Allanite
Colors / Varieties: 
  • Dark green, brownish green, black (darker colors with increasing iron content). Transparency: Transparent to Opaque.
  • Chrome rich green: Tawmawite
Crystal System / Forms: 
Monoclinic System / Prismatic crystals with vertical striations.
Hardness: 
6.5
Specific Gravity: 
3.40
Cleavage / Fracture: 
1 directional prismatic cleavage / Conchoidal fracture
Optic Character: 
Anisotropic, D.R.; Biaxial negative (may show pseudo-uniaxial)
Lustre: 
Vitreous
Refractive Index / Birefringence: 
1.729 - 1.768 / 0.019 - 0.045
Pleochroism: 
Strong (green, brownish red, yellow)
Dispersion: 
0.030
Magnification: 
Parallel needle inclusions, strong doubling of facet edges and inclusions, color zoning.
U.V. Fluorescence: 
Inert
Spectrum: 
455nm, 475nm (Directional)
Cause of Color: 
Iron
Specific Tests: 
The strong reddish brown pleochroic color is often mistaken for a color change phenomena.
Simulants (with separation tests): 
Tourmaline (R.I., S.G., spectrum), Kornerupine (R.I., S.G., spectrum), Sillimanite (R.I., S.G., spectrum, pleochroism)
Geological Occurrence: 
Generally in low to medium grade metamorphic rocks and igneous rocks.
Sources: 
U.S.A., Sri Lanka, India, Myanmar, Madagascar, Austria, Norway, Switzerland.
Cuts & Uses: 
Facetted, cabochons, etc.