Calcite

Class: Carbonates (Nitrates)
Group: Calcite

Varieties | Names:

A major rock-forming mineral; in limestones, marbles, a common cement in sedimentary rocks, and as gangue in hydrothermal veins; in alkalic to mafic igneous rocks; common as speleothems in caves (Anthony et al., 2001—2005). There are specimens of 4440 carats (Arem, 1987: 60).

Calcite — specimen 0433, photo © NMNHS

Original description: ‘Calcit’ Freiesleben, J. C., 1836. Calcit — Magazin für die Oryktographie von Sachsen 7: 118—121 [view in ‘Library’].

Type locality: unknown.

Type material: unknown.

Etymology: from the Latin calx, for lime.

Distribution: abundant worldwide; a few of the many localities include: Democratic Republic of the Congo: Katanga; England: Cumbria, Cleator Moor; Germany: Saxony, Freiberg; Mexico: Charcas; Chihuahua, Santa Eulalia; Namibia: Tsumeb; Russia: Primorsky Krai, Dalnegorsk; USA: Missouri, Jasper Co., at Joplin, many mines in Reynolds Co.; Tennessee, Elmwood mine (Anthony et al., 2001—2005).

Chemistry

CaCO3

Essential elements: carbon (C), oxygen (O), calcium (Ca).

Crystal data

Crystallography: trigonal — hexagonal scalenohedral. Crystal habit: well-formed crystals are common, {1011}, {2131}, thin to thick tabular {0001}, with combinations of over 1000 forms noted, to 7 m; granular, in concretions, massive. Twinning: on {0112}, {1011}, {0001}, {0221} as twin and composition planes (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {1011}, perfect (Anthony et al., 2001—2005). Fracture: conchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 3 (Arem, 1987: 60). Density: 2.67—2.73 g/cm3 (Lazzarelli, 2012). Luminescence: may fluoresce red, blue, yellow, and other colours under UV; phosphorescent, cathodoluminescent, thermoluminescent, rarely triboluminescent (Anthony et al., 2001—2005).

Optical properties

Colour: colourless or white, also grey, yellow, green, many other colours from included minerals; colourless in transmitted light (Anthony et al., 2001—2005). Diaphaneity: transparent to opaque (Anthony et al., 2001—2005). Lustre: vitreous; pearly on cleavages and on {0001} (Anthony et al., 2001—2005). Refractive index: 1.486—1.658 — anisotropic [uniaxial (-)] (Lazzarelli, 2012). Birefringence: 0.172. Dispersion: very strong (Anthony et al., 2001—2005). Pleochroism: none (Arem, 1987: 60).

Material from ‘Repository’

4 specimens: 0192 — 4.14 ct, Thailand; 0254 — 2.71 ct, Thailand; 0433 — 1.45 ct, Kazakhstan; 0613 — 44.45 ct, no locality data.

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