Danburite

Short description: Tectosilicate mineral

Danburite

Cluster of creamy crystals of danburite

General
Category| Tectosilicates
Formula
(repeating unit)| CaB2(SiO4)2
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
Vitreous to greasy|re|er}}| 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
Ultraviolet fluorescence| Fluorescent and thermoluminescent (red); Short UV=violet blue; Long UV=blue to blue-green
References| [1][2][3]

Danburite is a calcium boron silicate mineral with a chemical formula of CaB2(SiO4)2.[5]

It has a Mohs hardness of 7 to 7.5 and a specific gravity of 3.0.[5] The mineral has an orthorhombic crystal form.[5] It is usually colourless, like quartz, but can also be either pale yellow[5] or yellowish-brown. It typically occurs in contact metamorphic rocks.

The Dana classification of minerals categorizes danburite as a sorosilicate, while the Strunz classification scheme lists it as a tectosilicate;[3] its structure can be interpreted as either.

Its crystal symmetry and form are similar to topaz; however, topaz is a calcium 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.[5]

Danburite from Mexico, ≈ 4 cm in height

## References

1. ↑ Danburite data on Webmineral
2. ↑ "Danburite in The Handbook of Mineralogy". http://www.handbookofmineralogy.com/pdfs/danburite.pdf.
3. ↑ 3.0 3.1 Danburite on Mindat.org
4. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.
5. ↑ 5.0 5.1 5.2 5.3 5.4 Chisholm, Hugh, ed (1911). "Danburite". Encyclopædia Britannica. 7 (11th ed.). Cambridge University Press. p. 793.

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