Rhodonite

Rhodonite is a manganese inosilicate, with the formula (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 (its name comes from Ancient Greek ῥόδον (rhódon) 'rose'), often tending to brown due to surface oxidation. The rose-red hue is caused by the manganese cation (Mn2+).[5]

Rhodonite
Rhodonite from San Martín Mine, Chiurucu, Huallanca District, Bolognesi Province, Ancash, Peru
Specimen size: 53 mm × 52 mm × 40 mm (2.1 in × 2.0 in × 1.6 in)
General
CategoryInosilicate
Formula
(repeating unit)		(Mn2+, Fe2+, Mg, Ca)SiO3
IMA symbolRdn[1]
Strunz classification9.DK.05
Dana classification65.04.01.01
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H–M symbol)
Space groupP1
Unit cella = 9.758 Å, b = 10.499 Å, c = 12.205 Å; α = 108.58°, β = 102.92°, γ = 82.52°; Z = 20
Identification
ColorPink, rose-pink to brownish red, red, gray and yellow
Crystal habitTabular crystals, massive, granular
TwinningLamellar, composition plane {010}
CleavagePerfect on {110} and {110}, (110) ^ (110) = 92.5°; good on {001}
FractureConchoidal to uneven
Mohs scale hardness5.5–6.5
LusterVitreous to pearly
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3.57–3.76
Optical propertiesBiaxial (+)
Refractive indexnα = 1.711–1.738, nβ = 1.714–1.741, nγ = 1.724–1.751
Birefringenceδ = 0.013
PleochroismWeak
2V angle58° to 73° (measured), 58° (calculated)
Alters toExterior commonly black from manganese oxides
References[2][3][4]

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 is 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 the Commonwealth of Massachusetts.[6]

See also

References
  1. Warr, L. N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Handbook of Mineralogy.
  3. Rhodonite, Mindat.org.
  4. Rhodonite, Webmineral data.
  5. "Minerals Colored by Metal Ions". minerals.gps.caltech.edu. Retrieved 2023-02-28.
  6. General Laws of Massachusetts, Chapter 2, Section 15 Archived 2008-11-23 at the Wayback Machine.

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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