Rhodonite

Rhodonite

Rhodonite crystals in rock
General
Category Inosilicate
Formula
(repeating unit)		 (Mn2+,Fe2+,Mg,Ca)SiO3
Strunz classification 9.DK.05
Dana classification 65.04.01.01
Crystal system Triclinic
Crystal class Pinacoidal (1)
(same H-M symbol)
Space group P1
Unit cell a = 9.758 Å, b = 10.499 Å
c = 12.205 Å; α = 108.58°
β = 102.92°, γ = 82.52°; Z = 20
Identification
Color Rose-pink to brownish red, gray, or yellow
Crystal habit Tabular crystals, massive, granular
Twinning Lamellar, composition plane {010}
Cleavage Perfect on {110} and {110}, (110) ^ (110) = 92.5°; good on {001}
Fracture Conchoidal to uneven
Mohs scale hardness 5.5 - 6.5
Luster Vitreous to pearly
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.57 - 3.76
Optical properties Biaxial (+)
Refractive index nα = 1.711 - 1.738 nβ = 1.714 - 1.741 nγ = 1.724 - 1.751
Birefringence δ = 0.013
Pleochroism Weak
2V angle Measured: 58° to 73°, Calculated: 58°
Alters to Exterior commonly black from manganese oxides
References [1][2][3]

Rhodonite is a manganese inosilicate, (Mn, Fe, Mg, Ca)SiO3 and member of the pyroxenoid group of minerals, crystallizing in the triclinic system. It commonly occurs as cleavable to compact masses with a rose-red color (the name comes from the Greek ῥόδος rhodos, rosy), often tending to brown because of surface oxidation.

Rhodonite crystals often have a thick tabular habit, but are rare. It has a perfect, prismatic cleavage, almost at right angles. The hardness is 5.5–6.5, and the specific gravity 3.4–3.7; luster is vitreous, being less frequently pearly on cleavage surfaces. The manganese is often partly replaced by iron, magnesium, calcium, and sometimes zinc which may sometimes be present in considerable amounts; a greyish-brown variety containing as much as 20% of calcium oxide is called bustamite; fowlerite is a zinciferous variety containing 7% of zinc oxide.

Pink rhodonite contrasting with black manganese oxides is sometimes used as gemstone material as seen in this specimen from Humboldt County, Nevada.

The inosilicate (chain silicate) structure of rhodonite has a repeat unit of five silica tetrahedra. The rare polymorph pyroxmangite, formed at different conditions of pressure and temperature, has the same chemical composition but a repeat unit of seven tetrahedra.

Rhodonite has also been worked as an ornamental stone. In the iron and manganese mines at Pajsberg near Filipstad and Långban in Värmland, Sweden, small brilliant and translucent crystals (pajsbergite) and cleavage masses occur. Fowlerite occurs as large, rough crystals, somewhat resembling pink feldspar, with franklinite and zinc ores in granular limestone at Franklin Furnace in New Jersey.

Rhodonite is the official gemstone of Commonwealth of Massachusetts.[4]

See also

References

  1. ↑ Handbook of Mineralogy
  2. ↑ Rhodonite, Mindat.org
  3. ↑ Rhodonite, Webmineral data
  4. ↑ General Laws of Massachusetts, Chapter 2, Section 15.

 This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Rhodonite". Encyclopædia Britannica (11th ed.). Cambridge University Press. 

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