Rhodonite

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Rhodonite crystals in rock

A piece of rounded rhodonite

Rhodonite is a manganese inosilicate, (Mn,Fe,Mg,Ca)SiO₃ and member of the pyroxene group of minerals, crystallizing in the triclinic system. It commonly occurs as cleavable to compact masses with a rose-red color, 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.

Rhodonite has also been worked as an ornamental stone. In the iron and manganese mines at Pajsberg near Filipstadt 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.

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.

Pink rhodonite contrasting with black manganese oxides is sometimes used as a gem material as seen in this specimen from Humboldt Co., Nevada, USA

Rhodonite is the official gem of Commonwealth of Massachusetts ^[1].

[edit] References

1. ^ M.G.L. - Chapter 2, Section 15

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