Rhodonite: Gemstone Information
Rhodonite is CaMn4Si5O15 and forms transparent to translucent rose pink to brownish red triclinic crystals. Commonly tabular or cleavable masses. The hardness is 5.5–6.5 and there are two directions of perfect cleavage. The SG is 3.67 for crystals and 3.57–3.76 for masses. The RI for the alpha, beta and gamma rays is 1,711–1.734, 1.716–1.739, 1.724–1.748 biaxial positive with birefringence 0.013. Absorption band at 548 nm with strong line at 503 nm and weak band at 455 nm. Masses often show black veining from undifferentiated manganese oxides. Facetable crystals are rare but show a beautiful red. Rhodonite occurs in manganese deposits formed by hydrothermal contact and regional metamorphism.Gem crystals usually from Broken Hill, New South Wales, Australia, or from Morro da Mina, Conselheiro Lafaiete, Minas Gerais, Brazil. Some facetable material also from Honshu, Japan, and good colour masses from Daghazeta, Tanzania. Rhodonite from Ekaterinburg, Urals, Russia,features in Fabergé and other artefacts.