Danburite

Danburite is one of the least known of the colourless gems , though it makes a very good jewellery stone. It is a calcium aluminium borate silicate by chemical composition and is quite a hard material, with a rating of 7 on the Mohs scale. Since it has a moderately high refractive index (about the same as tourmaline) danburite can can be faceted with good results. Danburite is primarily a collectors gemstone. It is usually colourless; yellow and light pink gems are seldom cut. Danburite is named after the city of Danbury, Connecticut, where this mineral was first described, though no gem grade material has come from Danbury. Danburite has good hardness and facets well, but its lack of fire in colourless stones limits its use as a mainstream gemstone. In 1839 American mineralogist Charles Upham Shephard observed a clear, bright, colourless gemstone in Danbury, Connecticut, and named it danburite after the location. Unfortunately for danburite, it turned into found at a time while coloured gems have been closely promoted and distinctly favored. This colourless find, therefore, did not create tons exhilaration at that point. Danburite, which belongs to a category of minerals called silicates, remained fantastically unknown for years, however is steadily growing in popularity nowadays. Chemical Formula CaB 2 Si 2 O 8 Colour Colourless, Yellow, Pink Hardness 7 Crystal System Orthorhombic Refractive Index 1.63 SG 2.9 - 3.0 Transparency Transparent Double Refraction -.007 Luster Vitreous Cleavage 1,1 Mineral Class Danburite
Sumber http://barokongnetwork.blogspot.com