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.[2]