Scolecite

Class: Silicates
Group: Zeolite

Primarily in cavities in basalts; in gneisses and amphibolites, and in dikes derived from syenitic magmas (Anthony et al., 2001—2005). Extreme rarity as faceted specimens.

Scolecite — specimen 0068, photo © NMNHS

Original description: ‘Scolezit’ Gehlen, A. F., Fuchs, J. N., 1813. Ueber Werner’s Zeolith, Hauy’s Mesotype und Stilbite — Journal für Chemie und Physik 8 (4): 360—361 [view in ‘Library’].

Type locality: unknown.

Type material: unknown.

Etymology: from the Greek word σκώληξ (skolex), worm, in reference to the mineral’s reaction to the blowpipe flame.

Distribution: Austria: Carinthia; Brazil; Iceland; India: Poona; Mexico; Scotland; Switzerland (Anthony et al., 2001—2005).

Chemistry

CaAl2Si3O10·3H2O

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

Crystal data

Crystallography: monoclinic — domatic. Crystal habit: crystals are slender prismatic, may be square in cross section, to 30 cm. Twinning: on {100}, twin axis [001], common, as contact or penetration twins (Anthony et al., 2001—2005).

Physical properties

Cleavage: {110} and {110}, perfect (Anthony et al., 2001—2005). Fracture: uneven (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 5—5.5 (Lazzarelli, 2012). Density: 2.2—2.23 g/cm3 (Lazzarelli, 2012). Luminescence: may fluoresce yellow to brown under SW and LW UV (Anthony et al., 2001—2005). Other: pyroelectric, piezoelectric (Anthony et al., 2001—2005).

Optical properties

Colour: colourless to white; colourless 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: 1.512—1.523 — anisotropic [biaxial (-)] (Lazzarelli, 2012). Birefringence: 0.011. Dispersion: strong (Anthony et al., 2001—2005). Pleochroism: none.

Material from ‘Repository’

1 specimen: 0068 — 0.54 ct, India.

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