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Class: Silicates

In iron-rich metamorphic rocks; in metamorphosed iron formations (Anthony et al., 2001—2005). Constituent of nephrite.
Nephrite — specimen 0598
Nephrite — specimen 0598, photo © NMNHS

Original description: ‘ferroactinolite’ Sundius, N., 1946. The classification of the hornblendes and the solid solution relations in the amphibole group — Sveriges Geologiska Undersökning 40 (4): 7 [view in ‘Library’].

Type locality: unknown.

Type material: unknown.

Etymology: named for its similarity to actinolite.

Distribution: probably widespread, but many locality references lack qualifying chemical analyses (Anthony et al., 2001—2005).



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

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: as bladed or columnar crystals; granular to massive. Twinning: simple or lamellar (Anthony et al., 2001—2005).

Physical properties

Cleavage: perfect on {110} (Anthony et al., 2001—2005). Fracture: no data. Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 5—6 (Anthony et al., 2001—2005). Density: 3.24—3.48 g/cm3 (Anthony et al., 2001—2005). Luminescence: none.

Optical properties

Colour: dark green; in thin section yellow-green or blue-green (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous (Anthony et al., 2001—2005). Refractive index: 1.668—1.702 — anisotropic [biaxial (-)] (Anthony et al., 2001—2005). Birefringence: 0.034. Dispersion: weak (Anthony et al., 2001—2005). Pleochroism: moderate to strong (Anthony et al., 2001—2005).

Material from ‘Repository’

1 specimen: 0598 — 2.79 ct, Russia, Siberian District, Eastern Sayan.

Gallery view