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Class: Phosphates, arsenates, vanadates
Group: Amblygonite

A late primary and secondary mineral in zoned granite pegmatites; may be an ore of lithium (Anthony et al., 2001—2005). Faceted specimens are relatively rare.

Original description: Des Cloizeaux, A., 1871. Note sur la Montebrasite — Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences 73: 306 [view in ‘Library’].

Type locality: Montebras mines, Montebras, Soumans, Creuse, Nouvelle-Aquitaine, France (Des Cloizeaux, 1871: 306).

Type material: unknown.

Etymology: for the type locality, Montebras, France.

Distribution: Brazil: Minas Gerais; Canada; France; Sweden; USA (Anthony et al., 2001—2005).



Essential elements: hydrogen (H), lithium (Li), oxygen (O), aluminium (Al), phosphorus (P).

Crystal data

Crystallography: triclinic — pinacoidal. Crystal habit: crystals typically equant, may be short to long prismatic, to 10 cm; as coarse cleavable or blocky to rounded nodular masses. Twinning: common on {111}, producing tabular composite crystals (Anthony et al., 2001—2005).

Physical properties

Cleavage: perfect on {100}, good on {110}; distinct on {011} (Anthony et al., 2001—2005). Fracture: uneven to subconchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 5.5—6 (Anthony et al., 2001—2005). Density: 2.98—3.04 g/cm3 (Anthony et al., 2001—2005). Luminescence: none.

Optical properties

Colour: pale brown, pink, pale yellow, grey, white, colourless; colourless in transmitted light (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous, pearly on cleavages (Anthony et al., 2001—2005). Refractive index: 1.594—1.646 — anisotropic [biaxial (+/-)] (Anthony et al., 2001—2005). Birefringence: 0.022—0.03. Dispersion: no data. Pleochroism: none.

Material from ‘Repository’

1 specimen: 0542 — 0.39 ct, France.

Gallery view