Danburite

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Danburite
Cluster of creamy crystals of danburite
Tectosilicate minerals
CaB2(SiO4)2
Dbu
Grandfathered (1839)
9.FA.65
56.3.1.1
Orthorhombic
Rhombic dipyramidal (mmm)
Pnam (no. 62)
a = 8.038(3), b = 8.752(5) c = 7.73 [Å]; Z = 4
Colourless, white, gray, brownish white, straw yellow
Euhedral prismatic crystals; disseminated masses
{001} Poor
Subconchoidal to uneven
Brittle
7 – 7.5
Vitreous to greasy
White
Transparent to translucent
2.93 – 3.02
Biaxial (+/-)
nα = 1.627 – 1.633 nβ = 1.630 – 1.636 nγ = 1.633 – 1.639
δ = 0.006
88 to 90° measured
r < v strong
Fluorescent and thermoluminescent (red); Short UV=violet blue; Long UV=blue to blue-green

Danburite is a calcium boron silicate mineral with a chemical formula of CaB2(SiO4)2.

It has a Mohs hardness of 7 to 7.5 and a specific gravity of 3.0. The mineral has an orthorhombic crystal form. It is usually colourless, like quartz, but can also be either a cheese-like pale yellow or yellowish-brown. It typically occurs in contact metamorphic rocks.

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The Dana classification of minerals categorizes danburite as a sorosilicate, while the Strunz classification scheme lists it as a tectosilicate; its structure can be interpreted as either.

Its crystal symmetry and form are similar to topaz; however, topaz is an aluminum fluorine bearing nesosilicate. The clarity, resilience, and strong dispersion of danburite make it valuable as cut stones for jewelry.

It is named for Danbury, Connecticut, United States, where it was first discovered in 1839 by Charles Upham Shephard.

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