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Class: Borates

Occurs in borate deposits (Anthony et al., 2001—2005).
Howlite — specimen 0018
Howlite — specimen 0018, photo © NMNHS

Original description: How, H., 1868. II. Contributions to the Mineralogy of Nova Scotia. III. Borates and other Minerals in Anhydrite and Gypsum. Silicoborocalcite, a New Mineral — The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 35: 32—41 [view in ‘Library’].

Type locality: near Windsor, Nova Scotia, Canada.

Type material: unknown.

Etymology: after Henry How, Canadian chemist, geologist, and mineralogist, who first described the species.

Distribution: Canada: Nova Scotia; Mexico: Sonora; Serbia; Turkey; USA: California (Anthony et al., 2001—2005).



Essential elements: hydrogen (H), boron (B), oxygen (O), silicon (Si), calcium (Ca).

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: crystals tabular, flattened on {100}, with {100} dominant and terminated by {011} and {001}, to 1 cm; most commonly nodular (Anthony et al., 2001—2005).

Physical properties

Cleavage: none. Fracture: conchoidal, uneven. Tenacity: no data. Hardness: 3.5 (Anthony et al., 2001—2005). Density: 2.53—2.59 g/cm3 (Anthony et al., 2001—2005). Luminescence: none.

Optical properties

Colour: white; in thin section, colourless (Anthony et al., 2001—2005). Diaphaneity: translucent in thin fragments (Anthony et al., 2001—2005). Lustre: subvitreous (Anthony et al., 2001—2005). Refractive index: 1.583—1.6 — anisotropic [biaxial (-)] (Anthony et al., 2001—2005). Birefringence: 0.017. Dispersion: no data. Pleochroism: none.

Material from ‘Repository’

1 specimen: 0018 — 5.41 ct, USA.

Gallery view