Rhodochrosite

Class: Carbonates (Nitrates)
Group: Calcite

A primary mineral in hydrothermal veins; in metamorphic deposits; common in carbonatites; authigenic and secondary in sediments; uncommon in granite pegmatites (Anthony et al., 2001—2005). Faceted specimens are rare. The largest faceted specimen is a 59.65 carat from South Africa (Arem, 1987: 162).

Rhodochrosite — specimen 0028, photo © NMNHS

Original description: ‘Rhodochrosit’ Hausmann, J. F. L., 1813. Rhodochrosit — Handbuch der Mineralogie, Göttingen 3: 1081—1082 [view in ‘Library’].

Type locality: Cavnic mine, Cavnic, Maramureș, Romania.

Type material: unknown.

Etymology: derived from the Greek words ρόδο (rhodo) ‘rose’ and χρώς (chros) ‘colouring’, referring to its colour.

Distribution: numerous localities; only a few for good specimens: Canada: Quebec, Mont Saint-Hilaire; China: Guangxi Zhuang, Wuzhou, Cangwu, Liubao, Wutong mine; Mexico: Chihuahua, Santa Eulalia; Sonora, Cananea; Peru: Lima, Cajatambo Province, Uchucchacua; South Africa: Cape Province, near Kuruman, Hotazel mine; USA: Colorado, Park Co., Alma, Sweet Home mine (Anthony et al., 2001—2005).

Chemistry

Mn2+CO3

Essential elements: carbon (C), oxygen (O), manganese (Mn).

Crystal data

Crystallography: trigonal — hexagonal scalenohedral. Crystal habit: crystals are rhombohedra {1011} or scalenohedra {2131}, to 12 cm, modified by {0001}, {1010}, {1120}, with several other forms, may be rounded or saddle-shaped; commonly in bladed aggregates, columnar, botryoidal, compact granular, massive. Twinning: on {1012}, contact and lamellar, then flattened (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {1011}, perfect (Anthony et al., 2001—2005). Fracture: uneven to conchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Arem, 1987: 162). Hardness: 3.5—4 (Arem, 1987: 162). Density: 3.45—3.7 g/cm3 (Lazzarelli, 2012). Luminescence: none. Other: slightly soluble in water with the solubility rate increasing with the presence of carbon dioxide; soluble with effervescence in warm acids.

Optical properties

Colour: pink, rose-red, cherry-red, yellow, yellowish grey, cinnamon-brown, may be banded; colourless in transmitted light (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous; pearly in aggregates (Anthony et al., 2001—2005). Refractive index: 1.578—1.82 — anisotropic [uniaxial (-)] (Lazzarelli, 2012). Birefringence: 0.208—0.22. Dispersion: 0.015 (low). Pleochroism: faint (Arem, 1987: 162).

Material from ‘Repository’

1 specimen: 0028 — 0.50 ct, China, Guangxi Zhuang, Wuzhou, Cangwu, Wutong mine, 23.81°N 111.378°E.

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