Clinohumite

Class: Silicates
Group: Humite

In contact metamorphic zones in dolomite rocks and metasomatised limestones adjacent to felsic rocks; in serpentine and talc schists; in carbonatites (Anthony et al., 2001—2005). Faceted specimens are rare.

Clinohumite — specimen 0045, photo © NMNHS

Original description: ‘Klinohumit’ Des Cloizeaux, A. L. O. L., 1876. 3. Typus. Klinohumit — Neues Jahrbuch für Mineralogie, Geologie und Palaontologie 1876: 643—645 [view in ‘Library’].

Type locality: Monte Somma, Somma-Vesuvius Complex, Naples Province, Campania, Italy.

Type material: Muséum national d’Histoire naturelle, Paris, France, 106.395—106.556; National Museum of Natural History, Smithsonian Institution, Washington, DC, USA, 94997 (Anthony et al., 2001—2005).

Etymology: for its monoclinic crystal system and relation to humite.

Distribution: Canada: Ontario; Finland; Italy: Monte Somma and Vesuvius, Campania; Russia: near Lake Baikal; Spain; Tajikistan: Pamir; USA: California (Anthony et al., 2001—2005).

Chemistry

(Mg,Fe2+)9(SiO4)4(F,OH)2

Essential elements: hydrogen (H), oxygen (O), fluorine (F), magnesium (Mg), silicon (Si), iron (Fe).

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: crystals complex, highly modified, to 2 cm; massive. Twinning: common on {100}, simple, lamellar (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {100}, poor (Anthony et al., 2001—2005). Fracture: uneven to subconchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 6 (Arem, 1987: 113). Density: 3.13—3.75 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: white, yellow to brown; in thin section, colourless, pale yellow to golden yellow (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous (Anthony et al., 2001—2005). Refractive index: 1.623—1.728 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.024—0.041. Dispersion: 0.021. Pleochroism: X = golden yellow, yellow-brown, deep reddish yellow; Y = pale yellow, yellow-orange, light yellow; Z = pale yellow, yellow-orange, colourless (Anthony et al., 2001—2005).

Material from ‘Repository’

2 specimens: 0045 — 0.16 ct, Vietnam, Yên Bái, Lục Yên; 0458 — 0.41 ct, Tajikistan.

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