richterite

{{Infobox mineral | name = Richterite | category = Inosilicates | image = Richterite-mrz156a.jpg | caption = Richterite. Wilberforce, Monmouth Township, Haliburton County, Ontario, Canada. | formula = Na(NaCa)Mg5Si8O22(OH)2# | IMAsymbol = Rct | strunz = 9.DE.20 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = C2/m | color = Brown, yellow, red, or green | habit = Prismatic; acicular or asbestiform | twinning = Simple or multiple parallel to {100} | mohs = 5–6 | cleavage = Perfect | fracture = Uneven, brittle | luster = Vitreous | streak = Pale yellow | gravity = 3.0–3.5 | diaphaneity = Transparent to translucent | opticalprop = Biaxial (−) | refractive = nα = 1.615 nβ = 1.629 nγ = 1.636 | birefringence = δ = 0.021 | pleochroism = Strong: pale yellow, orange, and red | 2V = 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 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).