Elbaite

Class: Silicates
Group: Tourmaline

Varieties | Names:

In granites, granite pegmatites, and some metamorphic rocks; in high-temperature hydrothermal veins (Anthony et al., 2001—2005).

Elbaite — specimen 0444, photo © NMNHS

Original description: ‘Elbait’ Vernadsky, W., 1913. Über die chemische Formel der Turmaline — Zeitschrift für Krystallographie und Mineralogie 53: 273—288 [view in ‘Library’].

Type locality: Fonte del Prete, San Piero in Campo, Elba Island, Livorno Province, Tuscany, Italy.

Type material: unknown.

Etymology: after the type locality, the island of Elba, Italy.

Distribution: Afghanistan: Laghman; Brazil: Minas Gerais; Italy: around San Piero in Campo, Elba; Madagascar; Mozambique: Alto Ligonha district; Namibia; Pakistan: around Gilgit; Russia: Yekaterinburg district, Urals; USA: from the Pala district, San Diego Co., California (Anthony et al., 2001—2005).

Chemistry

Na(Li1.5,Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)

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

Crystal data

Crystallography: trigonal — ditrigonal pyramidal. Crystal habit: crystals prismatic to acicular, with prominent trigonal prism and pyramid, to 1.6 m; commonly hemimorphic, striated; also radial, fibrous, massive. Twinning: rare, on {1011} or {4041} (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {1120}, {1011}, very poor (Anthony et al., 2001—2005). Fracture: uneven to conchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 7 (Anthony et al., 2001—2005). Density: 2.9—3.1 g/cm3 (Anthony et al., 2001—2005). Luminescence: none. Other: pyroelectric and piezoelectric (Anthony et al., 2001—2005).

Optical properties

Colour: green, blue, red, orange, yellow, colourless; zoning common parallel to trigonal outline; colourless in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous to resinous (Anthony et al., 2001—2005). Refractive index: 1.614—1.666 — anisotropic [uniaxial (-)] (Lazzarelli, 2012). Birefringence: 0.014—0.032. Dispersion: 0.017. Pleochroism: O = pink, pale green, pale to deep blue; E = colourless, yellow, olive-green, purplish (Anthony et al., 2001—2005).

Material from ‘Repository’

36 specimens: 0533 — 0.38 ct, Nigeria; 0565 — 0.23 ct, Tanzania; 0663 — 0.22 ct, Tanzania; 0333 — 0.83 ct, Namibia; 0444 — 0.38 ct, Mozambique; 0003 — 1.81 ct, Mozambique; 0451 — 0.20 ct, Mozambique; 0564 — 0.29 ct, Nigeria; 0370 — 1.14 ct, Nigeria; 0730 — 0.33 ct, Tanzania; 0043 — 0.29 ct, no precise locality [Africa]; 0548 — 0.14 ct, no precise locality [Africa]; 0083 — 0.29 ct, no precise locality [Africa]; 0134 — 0.17 ct, no precise locality [Africa]; 0139 — 0.19 ct, no precise locality [Africa]; 0140 — 0.17 ct, no precise locality [Africa]; 0338 — 0.16 ct, no precise locality [Africa]; 0339 — 0.16 ct, no precise locality [Africa]; 0732 — 0.88 ct, Tanzania; 0105 — 0.48 ct, Mozambique; 0329 — 0.19 ct, no precise locality [Africa]; 0330 — 0.18 ct, no precise locality [Africa]; 0498 — 0.25 ct, Mozambique; 0448 — 0.42 ct, Nigeria; 0071 — 1.19 ct, Nigeria; 0153 — 0.92 ct, Nigeria; 0532 — 0.60 ct, Mozambique; 0328 — 1.02 ct, Mozambique; 0535 — 0.93 ct, no precise locality [Africa]; 0494 — 0.41 ct, Mozambique; 0628 — 1.28 ct, Mozambique; 0396 — 0.82 ct, Nigeria; 0069 — 1.75 ct, Mozambique; 0154 — 2.92 ct, Nigeria; 0395 — 0.62 ct, Nigeria; 0534 — 1.14 ct, Mozambique.

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