| Danburite | |
|---|---|
 Cluster of creamy crystals of danburite | |
| General | |
| Category | Tectosilicate |
| Formula | CaB2(SiO4)2 |
| IMA symbol | Dbu[1] |
| Strunz classification | 9.FA.65 |
| Dana classification | 56.3.1.1 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pnam |
| Unit cell | a = 8.038(3), b = 8.752(5) c = 7.73 [Å]; Z = 4 |
| Identification | |
| Colour | Colourless, white, gray, brownish white, straw yellow |
| Crystal habit | Euhedral prismatic crystals; disseminated masses |
| Cleavage | {001} Poor |
| Fracture | Subconchoidal to uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 7 – 7.5 |
| Lustre | Vitreous to greasy |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.93 – 3.02 |
| Optical properties | Biaxial (+/-) |
| Refractive index | nα = 1.627 – 1.633 nβ = 1.630 – 1.636 nγ = 1.633 – 1.639 |
| Birefringence | δ = 0.006 |
| 2V angle | 88 to 90° measured |
| Dispersion | r < v strong |
| Ultravioletfluorescence | Fluorescent and thermoluminescent (red); Short UV=violet blue; Long UV=blue to blue-green |
| References | [2][3][4] |
Danburite is acalciumboronsilicate mineral with achemical formula of CaB2(SiO4)2.[5]
It has aMohs hardness of 7 to 7.5 and aspecific gravity of 3.0.[5] The mineral has anorthorhombic crystal form.[5] It is usually colourless, like quartz, but can also be either pale yellow[5] or yellowish-brown. It typically occurs in contactmetamorphic rocks.
The Dana classification of minerals categorizes danburite as asorosilicate, while the Strunz classification scheme lists it as atectosilicate;[4] its structure can be interpreted as either.
Its crystal symmetry and form are similar totopaz; however, topaz is a calcium fluorine bearingnesosilicate. The clarity, resilience, and strong dispersion of danburite make it valuable as cut stones for jewelry.
It is named forDanbury, Connecticut,United States, where it was first discovered in 1839 by Charles Upham Shephard.[5]
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