Saturday, 10 December 2016

Danburite

What is 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.

History and Occurrence

In 1839 American mineralogist Charles Upham Shephard discovered a clear, bright, colourless gemstone in Danbury, Connecticut, and named it danburite after the location. Unfortunately for danburite, it was discovered at a time when coloured gemstones were heavily promoted and highly desired. This colourless find, therefore, didn't create much excitement at that time. Danburite, which belongs to a class of minerals known as silicates, remained relatively unknown for years, but is steadily growing in popularity today.

Properties of Danburite

Yellow Danburite
Chemical FormulaCaB2Si2O8
ColourColourless, Yellow, Pink
Hardness7
Crystal SystemOrthorhombic
Refractive Index1.63
SG2.9 - 3.0
TransparencyTransparent
Double Refraction-.007
LusterVitreous
Cleavage1,1
Mineral ClassDanburite