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Serendibite

Class: Silicates
Group: Rhönite

In skarns, affected by boron metasomatism, along the contact between carbonate rocks and granite (Anthony et al., 2001—2005). One of the rarest gemstones.

Original description: Prior, G. T., Coomáraswámy, A. K., 1903. Serendibite, a new borosilicate from Ceylon — Mineralogical Magazine 13: 224—227 [view in ‘Library’].

Type locality: Gangapitiya, Ambakotte, Central Province, Sri Lanka.

Type material: unknown.

Etymology: after Serendib, the old Arabic name for Sri Lanka.

Distribution: Canada: on the Melville Peninsula, Northwest Territories; Madagascar; Russia: Sakha Republic; Sri Lanka: Gangapitiya; Tanzania; USA (Anthony et al., 2001—2005).

Chemistry

Ca2(Mg,Al)6(Si,Al,B)6O20

Essential elements: boron (B), oxygen (O), magnesium (Mg), aluminium (Al), silicon (Si), calcium (Ca).

Crystal data

Crystallography: triclinic — pinacoidal. Crystal habit: rarely in small tabular crystals; as anhedral grains, to 2 cm, and aggregates. Twinning: polysynthetic on {011}, common (Anthony et al., 2001—2005).

Physical properties

Cleavage: good on {010}, {001} (Anthony et al., 2001—2005). Fracture: uneven. Tenacity: no data. Hardness: 6.5—7 (Lazzarelli, 2012). Density: 3.43—3.44 g/cm3 (Lazzarelli, 2012). Luminescence: none.

Optical properties

Colour: greyish blue-green to deep blue, green, or brown; in transmitted light, nearly colourless to pale yellow-green or blue (Anthony et al., 2001—2005). Diaphaneity: transparent (Anthony et al., 2001—2005). Lustre: vitreous (Anthony et al., 2001—2005). Refractive index: 1.696—1.702 — anisotropic [biaxial (-)] (Lazzarelli, 2012). Birefringence: 0.05. Dispersion: no data. Pleochroism: strong; X = pale yellow, yellow-green to blue-green; Y = almost colourless, pale yellow, blue, blue-green; Z = light to dark blue (Anthony et al., 2001—2005).

Material from ‘Repository’

2 specimens: 0438 — 0.48 ct, Myanmar, Mandalay, Mogok; 0437 — 0.58 ct, Myanmar, Mandalay, Mogok.


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