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Beryllonite

Class: Phosphates, arsenates, vanadates

As a rare secondary mineral in granite and alkalic pegmatites (Anthony et al., 2001—2005). Faceted specimens are very rare.

Original description: Dana, E. S., 1888. Preliminary notice of Beryllonite, a new mineral — American Journal of Science 136: 290—291 [view in ‘Library’].

Type locality: beryllonite locality (Mcallister occurrence) and Joe McKeen Mountain locality (McKean Farm), Stoneham, Oxford Co., Maine, USA.

Type material: Yale University, New Haven, Connecticut, USA, 3.1946 (Anthony et al., 2001—2005).

Etymology: for one of the major constituents in the composition, beryllium.

Distribution: Afghanistan: Laghman, Paprock; Brazil: Minas Gerais, Linópolis; Canada: Quebec, Mont Saint-Hilaire; USA: Maine, Oxford Co., near Stoneham (Anthony et al., 2001—2005).

Chemistry

NaBePO4

Essential elements: beryllium (Be), oxygen (O), sodium (Na), phosphorus (P).

Crystal data

Crystallography: monoclinic — prismatic. Crystal habit: tabular on {010} to short prismatic crystals; may have many forms, to 25 cm; also in spherical aggregates, fibrous, massive. Twinning: on {101}, contact and penetration twins; on {110} and {100} polysynthetic and pseudohexagonal stellate twins (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {010}, perfect; on {100}, good; on {101}, indistinct; on {001}, in traces (Anthony et al., 2001—2005). Fracture: conchoidal (Arem, 1987: 55). Tenacity: brittle (Arem, 1987: 55). Hardness: 5.5—6 (Arem, 1987: 55). Density: 2.79—2.87 g/cm3 (Lazzarelli, 2012). Luminescence: none (Arem, 1987: 55). Other: slowly soluble in acids.

Optical properties

Colour: colourless, white to pale yellow; colourless in transmitted light (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous to adamantine, may be pearly on {010} (Anthony et al., 2001—2005). Refractive index: 1.552—1.562 — anisotropic [biaxial (-)] (Lazzarelli, 2012). Birefringence: 0.009—0.01. Dispersion: 0.01 (Arem, 1987: 55). Pleochroism: none (Arem, 1987: 55).

Material from ‘Repository’

1 specimen: 0655 — 0.04 ct, USA, Maine, Oxford, near Stoneham.


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