Original description: Lucas, J. A. H., 1813. XIII. Cordierite (f.). (Iolithe (m)) — Tableau Méthodique Espèces Minérales, D’Hautel, Paris: 219—222 [
view in ‘Library’].
Type locality: Großer Arber, Zwiesel, Bavaria, Germany.
Type material: unknown.
Etymology: in honour of Pierre Louis Antoine Cordier, French mining engineer and geologist.
Distribution: Australia; Canada: Manitoba; Finland; Germany: Bavaria, Bodenmais; India; Madagascar: south of Antsirabe; Namibia: around Namib; Norway; Sri Lanka; Zimbabwe (
Anthony et al., 2001—2005).
Chemistry
Mg2Al4Si5O18
Essential elements: oxygen (O), magnesium (Mg), aluminium (Al), silicon (Si).
Crystal data
Crystallography: orthorhombic — dipyramidal.
Crystal habit: crystals short prismatic, striated, to 18 cm; typically granular to compact, massive.
Twinning: common on {110}, {130}, simple, lamellar, cyclical (
Anthony et al., 2001—2005).
Optical properties
Colour: blue, smoky blue, bluish violet; greenish, yellowish brown, grey; colourless to very pale blue in thin section (
Anthony et al., 2001—2005).
Diaphaneity: transparent to translucent (
Anthony et al., 2001—2005).
Lustre: vitreous (
Arem, 1987: 70).
Refractive index: 1.542—1.578 — anisotropic [biaxial (+/-)] (
Lazzarelli, 2012).
Birefringence: 0.008—0.012.
Dispersion: 0.017 (
Arem, 1987: 70).
Pleochroism: X = pale yellow, green; Y = violet, blue-violet; Z = pale blue (
Anthony et al., 2001—2005).
Material from ‘Repository’
7 specimens: 0025 — 0.21 ct, Tanzania;
0123 — 0.21 ct, Tanzania;
0214 — 0.18 ct, Tanzania;
0380 — 0.19 ct, Tanzania;
0381 — 0.19 ct, Tanzania;
0389 — 0.21 ct, Tanzania;
0390 — 0.20 ct, Tanzania.
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