Class: Silicates
Group: Epidote
Original description: Haüy, R. J., 1801. Epidote, (m.) c’est-à-dire, qui a reçu un accroissement — Traité de Minéralogie 3: 102—113 [
view in ‘Library’].
Type locality: Bourg d’Oisans, Isère, Rhône-Alpes, France.
Type material: Muséum national d’Histoire naturelle, Paris, France (
Anthony et al., 2001—2005).
Etymology: from the Greek
επιδοσιζ (еpidosis), ‘increase’, in allusion to the crystal characteristic of one longer side at the base of the prism.
Distribution: Austria: Knappenwand, Salzburg; France: Bourg d’Oisans, Isère; Italy: Piedmont; Namibia; Norway: Arendal; Pakistan: Tormiq (
Anthony et al., 2001—2005).
Chemistry
CaAl2(Fe2+,Al)Si3O12(OH)
Essential elements: hydrogen (H), oxygen (O), aluminium (Al), silicon (Si), calcium (Ca), iron (Fe).
Crystal data
Crystallography: monoclinic — prismatic.
Crystal habit: crystals prismatic, to 35 cm, commonly elongated and striated; fibrous, coarse to fine granular, massive.
Twinning: on {100}, contact, lamellar, common (
Anthony et al., 2001—2005).
Optical properties
Colour: pistachio-green to pale green, yellow, yellowish green, greenish yellow, greenish black; yellow-green in thin section (
Anthony et al., 2001—2005).
Diaphaneity: transparent to nearly opaque (
Anthony et al., 2001—2005).
Lustre: vitreous, pearly, somewhat resinous (
Anthony et al., 2001—2005).
Refractive index: 1.729—1.768 — anisotropic [biaxial (-)] (
Lazzarelli, 2012).
Birefringence: 0.014—0.045.
Dispersion: 0.03.
Pleochroism: strong; X = colourless, pale yellow, pale green; Y = greenish yellow; Z = yellowish green (
Anthony et al., 2001—2005).
Material from ‘Repository’