Epidote: Gemstones Information

Epidote, CaAl2 (Fe3,Al)Si3O12(OH) forms a series with clinozoisite and shares group membership with that mineral and with zoisite both of which are dealt with under their respective headings. Prismatic monoclinic crystals of epidote show one direction of perfect cleavage and have a hardness of 6–7. Gem epidote is transparent and a characteristic green known as pistachio. The SG is 3.38–3.49, the RI for the alpha, beta and gammarays is 1.715–1.751, 1.725–1.784 and 1.734–1.797 with a birefringence 0.015–0.049, negative. Epidote shows pleochroic colours colourless, pale yellow or yellow-green, and greenish yellow. A band at 455 nm is characteristic and may be accompanied by another band at 475 nm. Specimensneed to be examined in different directions for the bands to become visible.A chrome epidote (‘tawmawite’) is a deep greenstone showing strong pleochroism (emerald-green and bright yellow) which is found at Tawmaw in the Kachin Hills of Myanmar; gem-quality crystals are said to come from the Fungwe area of Zimbabwe. Specimens come also fromOutukumpu, Finland. The name unakite has been used to denote rocksconsisting of pink feldspar and green epidote; most specimens have originated in Zimbabwe.Epidote group minerals have a wide range of modes of occurrence.Most originate in low- to medium-grade metamorphic rocks.Epidote is a fairly common mineral and is found at many places in the alpine system of Austria