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www.mineralgallery.co.za Minerals A-E |
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Epidote |
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Name
Epidote
Chemistry
Ca2(Al, Fe)3(SiO4)3(OH), Calcium Aluminum Iron Silicate Hydroxide
Uses
As a gemstone or as a mineral specimen
Color
Color is green to yellowish or brownish green, also brown to black
Hardness
6.5-7
Specific gravity
3.3-3.5
Crystals
Monoclinic.
Accompanied by:
Feldspar, quartz
Fracture
Uneven.
Luster
Vitreous.
Cleavage
Perfect parallel to length of crystal.
Streak
White
Similar to:
Tourmaline.
Epidote is the principal member of a group of silicate minerals that occur most commonly inlow-grade, calcareous metamorphic rocks and also in igneous rocks,where they have altered from feldspar, pyroxene, and amphibole minerals. A calcium aluminosilicate, epidote forms pistachio-green to dark-green elongated crystals (monoclinic system), disseminated grains, or fibrous or granular masses that have perfect cleavage in one direction.
Epidote is a structurally complex mineral having both single silicate tetrahedrons, SiO4, and double silicate tetrahedrons, Si2O7. The formula of epidote could be expressed in a such a way so as to reflect this organization; Ca2(Al, Fe)Al2O(SiO4)(Si2O7)(OH). The two aluminums represent the parallel chains of AlO6 and AlO4(OH)2 octahedra that are the heart of the epidote structure. The silicate groups and extra ions connect the chains together. Since the chains are parallel, the crystals tend to be prismatic. The chains are arranged in parallel planes and the perfect cleavage breaks the bonds between these planes. Luster is vitreous.
