Antigorite

Class: Silicates
Group: Kaolinite-serpentine

Varieties | Names:

Commonly replaces ultramafic rocks; as a replacement of siliceous dolomite rock along contacts with diabase sills (Anthony et al., 2001—2005).

Antigorite — specimen 0296, photo © NMNHS

Original description: ‘Antigorit’ Schweizer, E., 1840. XIV. Ueber den Antigorit, ein neues Mineral — Annalen der Physik und Chemie 19: 595—599 [view in ‘Library’].

Type locality: Antigorio Valley, Ossola Valley, Piedmont, Italy; Geisspfad area, Binn Valley, Valais, Switzerland.

Type material: Eidgenössische Technische Hochschule Zürich [ETH Zürich], Zürich, Switzerland, Wi4868 (Anthony et al., 2001—2005).

Etymology: for the occurrence at Valle Antigorio, Italy.

Distribution: Australia; Austria; Canada; China; Italy: Piedmont; Japan; Scotland; USA (Anthony et al., 2001—2005).

Chemistry

(Mg,Fe2+)3Si2O5(OH)4

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

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: minute crystals, typically platy along [001], rarely elongated along [010]; commonly bladed or fibrous (Anthony et al., 2001—2005).

Physical properties

Cleavage: perfect on {001}, observed on {100} and {010} (Anthony et al., 2001—2005). Fracture: conchoidal or splintery (Anthony et al., 2001—2005). Tenacity: no data. Hardness: 5—5.5 (Lazzarelli, 2012). Density: 2.58—2.8 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: green, blue-green, white; colourless to pale green in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to opaque (Anthony et al., 2001—2005). Lustre: resinous, greasy, silky, waxy, earthy (Anthony et al., 2001—2005). Refractive index: 1.53—1.575 — anisotropic [biaxial (-)] (Lazzarelli, 2012). Dispersion: none. Pleochroism: none.

Material from ‘Repository’

10 specimens: 0144 — 2.20 ct, no precise locality [Africa]; 0296 — 1.93 ct, no precise locality [Africa]; 0155 — 3.48 ct, India; 0110 — 14.74 ct, Afghanistan; 0149 — 3.69 ct, India; 0151 — 5.05 ct, India; 0158 — 5.27 ct, India; 0152 — 5.12 ct, USA, Rhode Island; 0615 — 30.00 ct, China, Liaoning; 0614 — 39.79 ct, China, Liaoning.

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