Axinite-(Fe)

Class: Silicates
Group: Axinite

In regionally metamorphosed rocks, in contact metamorphosed rocks, and in pegmatites (Anthony et al., 2001—2005).

Axinite-(Fe) — specimen 0400, photo © NMNHS

Original description: ‘ferroaxinite’ Schaller, W. T., 1911. Mineralogical notes, Series I. Axinite from California — U.S. Geological Survey Bulletin 490: 37—47 [view in ‘Library’].

Type locality: Saint-Christophe-en-Oisans, Bourg d’Oisans, Isère, Rhône-Alpes, France.

Type material: unknown.

Etymology: from the Greek αξίνα (axina), for ‘axe’, in allusion to its crystal habit, and the iron in the formula.

Distribution: many localities; Brazil, France; Isère, Bourg d’Oisans; Mexico; Pakistan: Skardu; Russia: Ural Mountains; Switzerland; USA: California (Anthony et al., 2001—2005).

Chemistry

Ca4Fe2+2Al4[BSi8O30](OH)2

Essential elements: hydrogen (H), boron (B), oxygen (O), aluminium (Al), silicon (Si), calcium (Ca), iron (Fe).

Crystal data

Crystallography: triclinic — pinacoidal. Crystal habit: crystals typically flattened, axe-head-shaped, to 20 cm; granular, massive (Anthony et al., 2001—2005).

Physical properties

Cleavage: good on {100}, poor on {001}, {110}, and {011} (Anthony et al., 2001—2005). Fracture: uneven to conchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 6.5—7 (Anthony et al., 2001—2005). Density: 3.25—3.28 g/cm3 (Anthony et al., 2001—2005). Luminescence: none.

Optical properties

Colour: clove-brown, brown, plum-blue, pearl-grey; colourless to pale brown or blue in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous (Anthony et al., 2001—2005). Refractive index: 1.674—1.693 — anisotropic [biaxial (-)] (Anthony et al., 2001—2005). Birefringence: 0.009—0.011. Dispersion: strong. Pleochroism: none.

Material from ‘Repository’

3 specimens: 0400 — 0.41 ct, Brazil; 0277 — 0.61 ct, Pakistan; 0728 — 0.31 ct, Afghanistan.

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