Class: Silicates
Group: Humite
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).
Chemistry
(Mg,Fe2+)5(SiO4)2(F,OH)2
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).
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’