Richterite

Richterite
240px Richterite. Wilberforce, Monmouth Township, Haliburton County, Ontario, Canada.
General
Category	Inosilicates
Formula (repeating unit)	Na(NaCa)Mg5Si8O22(OH)2
Strunz classification	09.DE.20
Identification
Color	Brown, yellow, red, or green
Crystal habit	Prismatic; acicular or asbestiform
Crystal system	Monoclinic
Twinning	Simple or multiple parallel to {100}
Cleavage	Perfect
Fracture	Uneven, brittle
Mohs scale hardness	5-6
Luster	Vitreous
Streak	Pale yellow
Diaphaneity	Transparent to translucent
Specific gravity	3.0-3.5
Optical properties	Biaxial (-)
Refractive index	nα = 1.615 nβ = 1.629 nγ = 1.636
Birefringence	δ = 0.021
Pleochroism	Strong: pale yellow, orange, and red
2V angle	68° measured
References

Richterite is a sodium calcium magnesium silicate mineral belonging to the amphibole group. If iron replaces the magnesium within the structure of the mineral, it is called ferrorichterite; if fluorine replaces the hydroxyl, it is called fluororichterite. Richterite crystals are long and prismatic, or prismatic to fibrous aggregates, or rock-bound crystals. Colors of richterite range from brown, grayish-brown, yellow, brownish- to rose-red, or pale to dark green. Richterite occurs in thermally metamorphosed limestones in contact metamorphic zones. It also occurs as a hydrothermal product in mafic igneous rocks, and in manganese-rish ore deposits. Localities include Mont-Saint-Hilaire, Quebec, and Wilberforce and Tory Hill, Ontario, Canada; Långban and Pajsberg, Sweden; West Kimberley, Western Australia; Sanka, Myanmar; and, in the US, at Iron Hill, Colorado; Leucite Hills, Wyoming; and Libby, Montana. The mineral was named in 1865 for the German mineralogist Hieronymous Theodor Richter (1824–1898).

References

• Bonewitz, 2008, Smithsonian Rock and Gem