Danburite

Relatively rare mineral of the silicate and germanate class.

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Danburit danburite    
Yellow danburite from the USA

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Colourless danburites from Mexico

Danburite is hard and well suited for jewellery. However, due to it's rareness and the rather unexciting colour, it is hardly ever used.

Origin of name: named after the type locality Danbury, in Fairfield County, Connecticut, USA, by American mineralogist Charles Upham Shepard in 1839.

Synonyms and trade names: none

Can be confused with: most other colourless and yelloiwsh gems

Localities: mindat.org currenlty (2014) lists 149 deposits. Facetable danburite is rather rare. Deposits of gem quality danburite are found in Mexico, the USA, Russia, Burma, Sri Lanka and Madagascar.

Handling: danburite is hard and sports only poor cleavage. However, due to it's low melting point, danburite is very heat-sensitiv. Facet edges melt easily, so keep away from the blowpipe! Besides, danburite is rather brittle and susceptible to fluoric acid.                                      

Worth knowing: danburite phosphoresces red under the blowpipe and melts to a glassy, translucent pearl. In contact with borax it effervesces.
Source: Wikipedia

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Gemmological Properties of Danburite

Formula:
Ca[B2Si2O8]
Crystal system:
orthorhombic
Mohs hardness:
7-7.25
Specific gravity:
2.93-3.02
Refractive index:
1.627-1.639
Max. Birefringence:
0.006
Pleochroism:
weak
Luminiscence:
LW blue, bluegreen SW blueviolett, thermoluminesces red
Lustre:
vitreaus to greasy
Cleavage:
poor
Fracture:
uneven to weakly conchoidal
Colour:
colourless, white, grey, yellowish, brownish