Rutile

Class: Oxides & hydroxides
Group: Rutile

A common accessory mineral in igneous rocks, anorthosite, and granite pegmatites; in hydrothermally-altered rocks; in gneiss, schist, contact metamorphosed limestones; in clays, shales (Anthony et al., 2001—2005). Faceted specimens are very rare.

Rutile — specimen 0173, photo © NMNHS

Original description: ‘Rutil’ Ludwig, C. F., 1803. Rutil — Handbuch der Mineralogie nach A. G. Werner 1: 305—306 [view in ‘Library’].

Type locality: Horcajuelo de la Sierra, Madrid, Spain.

Type material: unknown.

Etymology: from the Latin rutilus, for red, a common colour of the mineral.

Distribution: many localities; a few for fine crystals: Austria: Styria, Herzogberg, near Modriach; Brazil: Bahia, Conquista, Ibitiara; Italy: Trentino-Alto Adige, Val di Vizze; Namibia: Omaruru, Giftkuppe mine; Switzerland: Ticino, Lodrino; USA: Arkansas, Hot Spring Co., at Magnet Cove; California, Mono Co., White Mountains, in the Champion mine; North Carolina, Alexander Co., at Stony Point (Anthony et al., 2001—2005).

Chemistry

TiO2

Essential elements: oxygen (O), titanium (Ti).

Crystal data

Crystallography: tetragonal — ditetragonal dipyramidal. Crystal habit: crystals prismatic, elongated and striated, to 25 cm, rarely dipyramidal, massive. Twinning: on {011}, common, or {031}, geniculated, reticulated; as contact twins with two, six, or eight individuals, cyclic, polysynthetic (Anthony et al., 2001—2005).

Physical properties

Cleavage: on {110} good; on {100} moderate; on {111} in traces (Anthony et al., 2001—2005). Fracture: conchoidal, subconchoidal, uneven (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 6—6.5 (Arem, 1987: 163). Density: 4.2—4.3 g/cm3 (Lazzarelli, 2012). Luminescence: none (Arem, 1987: 163).

Optical properties

Colour: reddish brown, red, pale yellow, pale blue, violet, rarely green, black (Anthony et al., 2001—2005). Diaphaneity: opaque, transparent in thin fragments (Anthony et al., 2001—2005). Lustre: adamantine to submetallic (Anthony et al., 2001—2005). Refractive index: 2.609—2.903 — anisotropic [uniaxial (+)] (Lazzarelli, 2012). Birefringence: 0.287. Dispersion: very strong (Lazzarelli, 2012). Pleochroism: distinct; red, brown, yellow, green (Anthony et al., 2001—2005).

Material from ‘Repository’

1 specimen: 0173 — 0.97 ct, Brazil.

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