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Class: Oxides & hydroxides
Group: Spinel

Varieties | Names:

A common mineral, formed at high-temperatures as an accessory in igneous rocks, principally basalts, kimberlites, peridotites, and in xenoliths; in regionally metamorphosed aluminum-rich schists; in regionally and contact metamorphosed limestones (Anthony et al., 2001—2005). The largest specimens include: Samarian spinel, over 500 carats, stored in the Central Bank of Iran, Tehran; 398.72 carat red spinel purchased in China in 1676 and stored in the Diamond Fund, Moscow; Timur ruby, 361 carats, part of the Crown Jewels of the United Kingdom.
Spinel — specimen 0014
Spinel — specimen 0014, photo © NMNHS

Original description: unknown.

Type locality: unknown.

Type material: unknown.

Etymology: from the Latin spinella, little thorn, in allusion to the spine-shaped octahedral crystals.

Distribution: many localities. Canada: Ontario, Burgess; Quebec, Wakefield; Germany: Eifel district, and at Bodenmais, Bavaria; Italy: Campania, Monte Somma and Vesuvius; Madagascar: Andrahomana, Ambinda, Besakoa, and many other places; Myanmar: around Mogok; Russia: Sakha, Aldan Shield, Emeldjak and Katalakhu deposits; Sri Lanka: Ratnapura and Elahera districts, and elsewhere; Tajikistan: Pamir Mts, Gorondarinskoye; USA: California, Riverside Co., near Midland, and at the Crestmore quarry; New Jersey, Sussex Co., Ogdensburg, Franklin and Sterling Hill, Orange Co., at many places from Amity and Edenville, Allegany Co., New York to Andover (Anthony et al., 2001—2005).



Essential elements: oxygen (O), magnesium (Mg), aluminium (Al).

Crystal data

Crystallography: isometric — hexoctahedral. Crystal habit: commonly as octahedra, to 30 cm, may show dodecahedron or cube faces, rarely as dodecahedra; coarse granular, rounded, massive. Twinning: on {111} as both twin and composition plane, the spinel law (Anthony et al., 2001—2005).

Physical properties

Cleavage: parting on {111} (Anthony et al., 2001—2005). Fracture: conchoidal, uneven to splintery (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 8 (Lazzarelli, 2012). Density: 3.54—3.7 g/cm3 (Lazzarelli, 2012). Luminescence: reds and pinks: crimson in LW UV and SW UV, red in X-rays, no phosphorescence; blue: inert in UV; deep purple: red in LW UV, essentially inert in SW UV, lilac in X-rays; pale blue and violet: green in LW UV and X-rays, essentially inert in SW UV.

Optical properties

Colour: colourless, brown, black; red, orange, yellow, green, blue, indigo, violet (Anthony et al., 2001—2005). Diaphaneity: transparent to nearly opaque (Anthony et al., 2001—2005). Lustre: vitreous, splendent to dull (Anthony et al., 2001—2005). Refractive index: 1.71—1.735 — isotropic (Lazzarelli, 2012). Dispersion: 0.02 (Arem, 1987: 177). Pleochroism: usually none; anomalous in some blue zincian varieties.

Material from ‘Repository’

22 specimens: 0477 — 0.56 ct, Myanmar, Mandalay, Mogok; 0496 — 0.44 ct, Myanmar, Mandalay, Mogok; 0608 — 0.49 ct, Myanmar; 0014 — 1.00 ct, Sri Lanka; 0456 — 0.37 ct, Sri Lanka; 0664 — 0.30 ct, Sri Lanka; 0041 — 0.10 ct, Tanzania; 0597 — 0.06 ct, Tanzania; 0462 — 0.32 ct, Myanmar; 0658 — 0.44 ct, Sri Lanka; 0384 — 0.13 ct, China; 0385 — 0.14 ct, China; 0463 — 1.41 ct, Thailand, Kanchanaburi, Bo Phloi; 0442 — 1.29 ct, Thailand, Kanchanaburi, Bo Phloi; 0648 — 1.08 ct, Thailand, Kanchanaburi, Bo Phloi; 0650 — 0.93 ct, Thailand, Kanchanaburi, Bo Phloi; 0666 — 1.42 ct, Thailand, Kanchanaburi, Bo Phloi; 0670 — 1.58 ct, Thailand, Kanchanaburi, Bo Phloi; 0665 — 1.88 ct, Thailand, Kanchanaburi, Bo Phloi; 0671 — 1.38 ct, Thailand, Kanchanaburi, Bo Phloi; 0672 — 1.36 ct, Thailand, Kanchanaburi, Bo Phloi; 0673 — 0.73 ct, Thailand, Kanchanaburi, Bo Phloi.

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