The best known color of precious gemstone epidote is “pistachio” green, and this massive mineral is also called pistacite, in reference to its color. The crystal system is monoclinic and its habit is long prismatic, often striated vertically. Precious gemstone epidote has a 0.030 dispersion and 3.4 specific gravity. The name epidote is from the Greek epidosis, meaning “adittion” or “increase,” which is believed to refer to the fact that some of the crystals faces of this mineral are longer than others. Precious gemstone epidote is famously known from Green Monster Mountain in Alaska, and also from India, Sri Lanka, and Brazil. Others sources are in India, Myanmar, Switzerland, Madagascar, Austria, Norway, and Pakistan. The chrome green variety of precious gemstone epidote is known as tawmawite, in which up to 11 percent of the aluminum in its formula is replaced by chromium.
With an even fracture and 6.5 hardness level, Precious gemstone epidote is a very common mineral, but a rare collector’s gem. Coming from the class of silicates with silica tetrahedra in pairs, it is composed from calcium iron aluminum silicate hydroxite. Precious gemstone epidote is available in a color of brownish green, yellow green, rich chrome green, black, and dark green. Despite its hardness and deep color, precious gemstone epidote is not commonly cut and polished as a precious gem because the large crystals are rarely clear enough to facet. For gem material, the refractive index is 1.736-1.770 and its birefringence is 0.34. Cushion and step cut are the most common faceted cuts. The luster of precious gemstone epidote is vitreous and its cleavage is perfect in one direction.
Natural gemstones like precious gemstone epidote is the chief member of a silicate mineral group, which normally occur in low-grade, calcareous metamorphic rocks and also in igneous rocks, where they have altered from feldspar, pyroxene, and amphibole minerals. As a calcium aluminosilicate, precious gemstone epidote forms pistachio-green fibrous or granular masses, disseminated grains, or dark green elongated crystals, which have perfect cleavage in one direction. With both single and double silicate tetrahedral groups, epidote is a structurally complex mineral. There is a strong pleochroism, showing yellow, green, and brown, depending on direction. Precious gemstone epidote often forms inclusions in quartz.
