Richterite
Richterite. Wilberforce, Monmouth Township, Haliburton County, Ontario, Canada.
General
Category	Inosilicates
Formula (repeating unit)	Na(NaCa)Mg5Si8O22(OH)2#
IMA symbol	Rct[1]
Strunz classification	9.DE.20
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Identification
Color	Brown, yellow, red, or green
Crystal habit	Prismatic; acicular or asbestiform
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	[2][3][4][5]

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 aggregate, 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-rich 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