Natrolite

Class: Silicates
Group: Zeolite

In cavities in basalts and related igneous rocks; fills seams in granite, gneiss, and syenite (Anthony et al., 2001—2005). Faceted specimens are very rare.

Natrolite — specimen 0588, photo © NMNHS

Original description: ‘Natrolith’ Klaproth, M. H., 1803. XV. Chemische Untersuchung des Natroliths — Der Gesellschaft Naturforschender Freunde zu Berlin, Neue Schriften 4: 243—248 [view in ‘Library’].

Type locality: Hohentwiel, Singen, Hegau, Baden-Württemberg, Germany.

Type material: unknown.

Etymology: from the Latin natron, for the sodium content.

Distribution: Canada; France; Germany; Norway; Russia: Kola Peninsula; USA: Bound Brook, New Jersey (Anthony et al., 2001—2005).

Chemistry

Na2[Al2Si3O10]·2H2O

Essential elements: hydrogen (H), oxygen (O), sodium (Na), aluminium (Al), silicon (Si).

Crystal data

Crystallography: orthorhombic — pyramidal. Crystal habit: crystals short to long prismatic, to 1 m. Twinning: on {110}, {011}, {031} (Anthony et al., 2001—2005).

Physical properties

Cleavage: {110}, perfect; parting on {010} (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—2.26 g/cm3 (Arem, 1987: 134). Luminescence: commonly fluoresces orange to yellow under UV (Anthony et al., 2001—2005). Other: pyroelectric, piezoelectric (Anthony et al., 2001—2005).

Optical properties

Colour: colourless, white, grey, bluish, yellowish, pink; colourless in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous to pearly (Anthony et al., 2001—2005). Refractive index: 1.478—1.493 — anisotropic [biaxial (+)] (Lazzarelli, 2012). Birefringence: 0.012—0.013. Dispersion: weak. Pleochroism: none.

Material from ‘Repository’

1 specimen: 0588 — 1.03 ct, USA, New Jersey, Somerset County, Bound Brook.

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