Clinozoisite is a complex Calcium Aluminum Silicate Hydroxide mineral with the chemical formula Ca2Al3[O|OH|SiO4|Si2O7]. It was first discovered in Tyrol, Austria in 1896. 
The best crystals of Clinozoisite are of a beautiful olive green color, however some stones are grey-green or a lighter yellow-green. But the crystals of Clinozoisite are typically very small. Also very few depositions of the Clinozoisite crystals produce gem quality Clinozoisite. The crystals of Clinozoisite derive their name from the crystals’ similarity to Zoisite and from their monoclinic crystal form.
(faceted; from Baja, California. Weight: 6.6 carats total for the two stones)
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Clinozoisite - Properties:
Clinozoisite contains 17 percent calcium, 17 percent aluminum, 18 percent silicon; trace amounts hydrogen and 45 percent oxygen and its molecular weight is 454.36 grams. Clinozoisite is classified as a sorosilicate mineral.
Clinozoisite displays monoclinic prismatic properties and can form slender columns similar to tourmaline. Clinozoisite can also occur in crystalline masses which display massive striations, also in fibrous form, otherwise as granular massive, acicular needles or in veins. Twinning in the Clinozoisite crystals in uncommon but if present is usually of lamellar nature. 
The cleavages on the Clinozoisite crystals are clean and sharp with irregular and uneven fracturing and perfect cleavage. The crystals of Clinozoisite are also quite brittle. However Clinozoisite by nature is quite hard with a Moh’s hardness of 6.5. Clinozoisite has a density between 3.2 g/cm3 and 3.3 g/cm3. The crystals display fluorescent properties and some pleochroism but are not radioactive. 
The color of Clinozoisite varies between yellow to golden yellow and yellowish green. Very rarely one can find Clinozoisite crystals which are completely green in color. Gray, red and pink colored Clinozoisite crystals also do occur but are extremely rare. Due to the inclusions in the Clinozoisite crystals they are never completely transparent. Hence the crystals of Clinozoisite vary between transparent and translucent. Clinozoisites have a vitreous luster which is often glassy on the cleavages. The dispersion of the Clinozoisite crystals is weak.
Clinozoisite crystals usually occur in low grade to medium grade metamorphosed igneous rocks as well as in sedimentary rocks. The largest crystals of Clinozoisite which were of gemstone quality were found in East Tyrol Austria. The gemstones of Clinozoisite from these areas are bright with a beautiful olive green coloring and with very little inclusion.
Clinozoisite forms a solid solution series with epidote, with substitution of Fe(III) ions or Al(III) ions - and some gemstones in the continuty display equal properties of both minerals, so that a distinction cannot be made as to which characteristic is predominant. 
A further variety of Clinozoisite is Chrome-Clinozoisite, which has chromium ions substituted for the aluminium. 
Clinozoisite - Occurrence:
Clinozoisite is a widespread mineral with several possible locations for good crystals. The best source of gem quality Clinozoisite is in Skardu District in Baltistan in Pakistan. The crystals of Clinozoisite from this region are small and have heavy inclusion but they have a beautiful olive green color hue and some larger crystals of Clinozoisite found in this area also have a golden yellow color.
Gem quality clinozoisite crystals have also been found in Austria, Czech Republic, Finland and Norway, Ireland, Madagascar, India, Canada, USA (California, Vermont, Nevada) and Mexico. 
Clinozoisite - Sources Referenced:
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