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Class: Silicates
Group: Humite

In contact metamorphic zones, in limestones, associated with felsic to alkalic rocks; in carbonatites (Anthony et al., 2001—2005). Faceted specimens are extremely rare.

Original description: ‘Chondrodit’ d’Ohsson, C. M., 1817. Undersokning Af någre Mineralier — Kongliga Svenska Vetenskaps-Akademiens Handlingar 1817: 206—210 [view in ‘Library’].

Type locality: Skräbböle quarry, Pargas, Western Finland, Finland.

Type material: unknown.

Etymology: from the Greek for ‘grain’, in allusion to its occurring in isolated grains.

Distribution: Canada: Bancroft, Ontario; Finland: Pargas; India; Italy: Monte Somma and Vesuvius, Campania; South Africa: Transvaal (Anthony et al., 2001—2005).



Essential elements: hydrogen (H), oxygen (O), fluorine (F), magnesium (Mg), silicon (Si), iron (Fe).

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: crystals rare, varied in habit, typically flattened, to 10 cm; commonly as rounded grains, massive. Twinning: on {001}, simple and lamellar (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {100} indistinct; parting on {001} (Anthony et al., 2001—2005). Fracture: uneven to subconchoidal. Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 6—6.5 (Lazzarelli, 2012). Density: 3.1—3.2 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: light yellow, yellow, brown, red; in thin section, pale yellow or brown to colourless (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous to resinous (Anthony et al., 2001—2005). Refractive index: 1.589—1.67 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.025—0.036. Dispersion: none. Pleochroism: X = colourless, very pale yellow, brownish yellow; Y = colourless, yellow-green; Z = colourless, pale green (Anthony et al., 2001—2005).

Material from ‘Repository’

1 specimen: 0062 — 1.04 ct, Tanzania.

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