Danburite

Danburite
Cluster of creamy crystals of danburite
General
CategoryTectosilicate minerals
FormulaCaB2(SiO4)2
IMA symbolDbu[1]
IMA statusGrandfathered (1839)
Strunz classification9.FA.65
Dana classification56.3.1.1
Crystal systemOrthorhombic
Crystal classRhombic dipyramidal (mmm)
Space groupPnam (no. 62)
Unit cella = 8.038(3), b = 8.752(5)
c = 7.73 [Å]; Z = 4
Identification
ColourColourless, white, gray, brownish white, straw yellow
Crystal habitEuhedral prismatic crystals; disseminated masses
Cleavage{001} Poor
FractureSubconchoidal to uneven
TenacityBrittle
Mohs scale hardness7 – 7.5
LustreVitreous to greasy
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.93 – 3.02
Optical propertiesBiaxial (+/-)
Refractive indexnα = 1.627 – 1.633 nβ = 1.630 – 1.636 nγ = 1.633 – 1.639
Birefringenceδ = 0.006
2V angle88 to 90° measured
Dispersionr < v strong
Ultraviolet fluorescenceFluorescent and thermoluminescent (red); Short UV=violet blue; Long UV=blue to blue-green
References[2][3][4]

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 a cheese-like pale yellow[5] or yellowish-brown. It typically occurs in contact metamorphic rocks.

Danburite from Mexico, ≈ 4 cm in height

The Dana classification of minerals categorizes danburite as a sorosilicate, while the Strunz classification scheme lists it as a tectosilicate;[4] 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.[5]

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Danburite data on Webmineral
  3. ^ "Danburite in The Handbook of Mineralogy" (PDF). Archived from the original (PDF) on 2022-05-11. Retrieved 2014-03-24.
  4. ^ a b Danburite on Mindat.org
  5. ^ a b c d e Chisholm, Hugh, ed. (1911). "Danburite" . Encyclopædia Britannica. Vol. 7 (11th ed.). Cambridge University Press. p. 793.
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