Class: Silicates
Group: Gadolinite-datolite
Original description: ‘Datolith’ Klaproth, M. H., 1806. Chemische Untersuchung des Datoliths — Neues allgemeines Journal der Chemie 6: 107—110 [
view in ‘Library’].
Type locality: Nødebro mine, Arendal, Aust-Agder, Norway.
Type material: unknown.
Etymology: from the Greek
δατεῖσθαι (dateisthai), to divide, in reference to the granular texture of massive varieties.
Distribution: Austria: Kratzenberg, Habachtal; Germany: at Sankt Andreasberg, Harz Mountains; Mexico: Charcas; Norway: near Arendal; Russia: Primorsky Krai, Dalnegorsk; USA: Lane quarry, Hampden Co., Massachusetts (
Anthony et al., 2001—2005).
Chemistry
CaBSiO4(OH)
Essential elements: hydrogen (H), boron (B), oxygen (O), silicon (Si), calcium (Ca).
Crystal data
Crystallography: monoclinic — prismatic.
Crystal habit: crystals typically short prismatic, with prominent {110}, {011}, or tabular on {010}, to 12 cm; botryoidal or globular, having columnar structure; granular to compact; cryptocrystalline (
Anthony et al., 2001—2005).
Optical properties
Colour: colourless or white, commonly with a greenish tinge; may be greyish, yellow, green, red, pink; in thin section, colourless (
Anthony et al., 2001—2005).
Diaphaneity: transparent to translucent, rarely opaque (
Anthony et al., 2001—2005).
Lustre: vitreous (
Arem, 1987: 78).
Refractive index: 1.621—1.675 — anisotropic [biaxial (-)] (
Lazzarelli, 2012).
Birefringence: 0.044—0.045.
Dispersion: 0.016 (
Arem, 1987: 79).
Pleochroism: none (
Arem, 1987: 79).
Material from ‘Repository’
1 specimen: 0168 — 1.12 ct, USA, Connecticut, Hartford County, Farmington.
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