Friedelite

Class: Silicates

In metamorphosed Mn-Fe deposits (Anthony et al., 2001—2005). Faceted specimens are extremely rare.

Friedelite — specimen 0086, photo © NMNHS

Original description: Bertrand, E., 1876. Sur un nouveau minéral des Pyrénees — Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences 82: 1167—1168 [view in ‘Library’].

Type locality: d’Azet Pass, Louron Valley, Hautes-Pyrénées, France.

Type material: unknown.

Etymology: for the noted French chemist and mineralogist, Charles Friedel.

Distribution: Australia; Austria: Tirol; France: Louron Valley; Kazakhstan; South Africa; Sweden; USA: at Franklin, New Jersey (Anthony et al., 2001—2005).

Chemistry

Mn8Si6O15(OH,Cl)10

Essential elements: hydrogen (H), oxygen (O), silicon (Si), chlorine (Cl), manganese (Mn).

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: as pseudohexagonal tablets, may be hemimorphic, to 1 cm; more rarely as slender needles or as fibrous or lamellar aggregates; massive. Twinning: universal, repeated about [110] and [110], composition plane {001}, giving pseudorhombohedral symmetry (Anthony et al., 2001—2005).

Physical properties

Cleavage: perfect on {0001} (Anthony et al., 2001—2005). Fracture: uneven (Arem, 1987: 100). Tenacity: brittle (Arem, 1987: 100). Hardness: 4—5 (Arem, 1987: 100). Density: 3.06—3.19 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: pale pink, brownish red, dark red, brown (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous (Arem, 1987: 100). Refractive index: 1.627—1.663 — anisotropic [uniaxial (-)] (Lazzarelli, 2012). Birefringence: 0.032—0.035. Dispersion: none. Pleochroism: none.

Material from ‘Repository’

1 specimen: 0086 — 0.35 ct, USA, New Jersey, Sussex County, Franklin.

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