Rhodonite
By Bob Farrar
The Mineral of the Month for November will be rhodonite. Named for the Greek word rhodon, for “rose”, it is not to be confused with rhodochrosite, which may be similar in appearance. Rhodonite is an interesting mineral for both mineral collectors and gem cutters. Rhodonite consists of manganese silicate, MnSiO3. Zinc-rich rhodonite is known as fowlerite. It crystalizes in the triclinic system, forming crystals that range from thick tabular to elongate prismatic, as well as flattened and
plate-like.
Rhodonite also commonly occurs as massive material. It ranges in color from various shades of pink to red, as well as brownish or grayish. Other physical properties include a hardness of 5.5 to 6, specific gravity of 3.4 to 3.7, and prismatic cleavage. Pyroxmangite has similar composition and physical properties, but can be distinguished by x-ray diffraction. Rhodonite’s greater hardness, crystal form, and insolubility in acid generally distinguish it from rhodochrosite. Rhodonite typically occurs in metamorphosed manganese deposits, as well as in ore veins. The most famous locality for crystalized rhodonite is Franklin, New Jersey. There, it occurs as pink tabular crystals embedded in calcitemeasuring up to 8 inches long by 2 inches across. Another famous locality is Broken Hill, New South Wales, Australia, where deep red crystals are found in a lead-zinc ore deposit. Superb material comes from a manganese deposit at Morro da Mina, Conselheiro Lafaiete, Minas Gerais, Brazil. Material from Conselheiro Lafaiete is sometimes labeled as pyroxmangite; both minerals are reported from this locality. Druses of plate-like rhodonite crystals occur in vugs in Peru. Deep pink massive material is found in Australia, where it grades into nambulite, a lithium-sodium-manganese silicate. Massive pink material with black manganese minerals is found at a number of localities, including Plainfield, Massachusetts and Fluvanna Co., Virginia. Rhodonite is a popular lapidary material. Most commonly, it is massive material used for cabochons and carving, though the material from Brazil is sometimes transparent enough to be faceted. Rhodonite is also popular with mineral collectors. Franklin, NJ is a classic locality. Specimens from this and many other localities make fine additions to any mineral collection.
plate-like.
Rhodonite also commonly occurs as massive material. It ranges in color from various shades of pink to red, as well as brownish or grayish. Other physical properties include a hardness of 5.5 to 6, specific gravity of 3.4 to 3.7, and prismatic cleavage. Pyroxmangite has similar composition and physical properties, but can be distinguished by x-ray diffraction. Rhodonite’s greater hardness, crystal form, and insolubility in acid generally distinguish it from rhodochrosite. Rhodonite typically occurs in metamorphosed manganese deposits, as well as in ore veins. The most famous locality for crystalized rhodonite is Franklin, New Jersey. There, it occurs as pink tabular crystals embedded in calcitemeasuring up to 8 inches long by 2 inches across. Another famous locality is Broken Hill, New South Wales, Australia, where deep red crystals are found in a lead-zinc ore deposit. Superb material comes from a manganese deposit at Morro da Mina, Conselheiro Lafaiete, Minas Gerais, Brazil. Material from Conselheiro Lafaiete is sometimes labeled as pyroxmangite; both minerals are reported from this locality. Druses of plate-like rhodonite crystals occur in vugs in Peru. Deep pink massive material is found in Australia, where it grades into nambulite, a lithium-sodium-manganese silicate. Massive pink material with black manganese minerals is found at a number of localities, including Plainfield, Massachusetts and Fluvanna Co., Virginia. Rhodonite is a popular lapidary material. Most commonly, it is massive material used for cabochons and carving, though the material from Brazil is sometimes transparent enough to be faceted. Rhodonite is also popular with mineral collectors. Franklin, NJ is a classic locality. Specimens from this and many other localities make fine additions to any mineral collection.
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