Russellite

Russellite is a bismuth tungstate mineral with the chemical formula Bi₂WO₆.^[1] It crystallizes in the orthorhombic crystal system. Russellite is yellow or yellow-green in color, with a Mohs hardness of ​3 ¹⁄₂.^[1]

Russellite
Yellow globular aggregates of the rare wolfram mineral russellite from the famous Clara Mine (Wolfach, Black Forest, Baden-Württemberg, Germany).
General
Category	Tungstate minerals
Formula (repeating unit)	Bi2WO6
Strunz classification	4.DE.15
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) H-M symbol: (mm2)
Space group	Pca21
Unit cell	a = 5.43 Å, b = 16.43 Å c = 5.45 Å; Z = 4
Identification
Color	Yellow-green, yellow
Crystal habit	Fine-grained, compact, massive
Mohs scale hardness	3.5
Specific gravity	7.33 - 7.37
Optical properties	Biaxial (+)
Refractive index	2.17 - 2.51
Dispersion	relatively strong
References	[1][2][3]

Russellite is named for the mineralogist Sir Arthur Russell, and the type locality is the Castle-an-Dinas Mine,^[1] near St Columb Major in Cornwall, where it was found in 1938 in wolframite.^[4] It occurs as a secondary alteration of other bismuth bearing minerals in tin - tungsten hydrothermal ore deposits, pegmatites and greisens. It typically occurs associated with native bismuth, bismuthinite, bismite, wolframite, ferberite, scheelite, ferritungstite, anthoinite, mpororoite, koechlinite, cassiterite, topaz, muscovite, tourmaline and quartz. 

This article uses material from the Wikipedia article  Metasyntactic variable, which is released under the  Creative Commons Attribution-ShareAlike 3.0 Unported License.