Brokite

Brookite
c 2001-2005 Mineral Data Publishing, version 1

TiO2

Crystal Data: Orthorhombic. Point Group: 2/m 2/m 2/m. As crystals, to 12 cm, typically tabular on {010} and elongated and striated[001]; rarely tabular on {001}; commonly pyramidal {111} or pseudohexagonal with {120} and {111}. Twinning: On {120}, uncertain. Physical Properties: Cleavage: {120}, indistinct; {001}, in traces.Fracture: Subconchoidal to irregular. Tenacity: Brittle. Hardness = 5.5–6 D(meas.) = 4.08–4.18 D(calc.) = 4.133 Optical Properties: Opaque to translucent, transparent in thin fragments. Color: Brown,yellowish brown, reddish brown; dark brown to iron-black; yellowish brown to dark brown in transmitted light. Streak: White to grayish white or yellowish white. Luster: Metallic adamantine tosubmetallic. Optical Class: Biaxial (+). Pleochroism: Very weak; yellowish, reddish, orange to brown. Orientation: Z = b. Dispersion: r > v, very strong, with crossed axial dispersion. Absorption: Z > Y > X. α =2.5831 β = 2.5843 γ = 2.7004 2V(meas.) = 0◦ –28◦ , variable with wavelength. Cell Data: Space Group: P cab. a = 5.4558 b = 9.1819 c = 5.1429 Z=8

X-ray Powder Pattern: Magnet Cove, Arkansas, USA.3.51 (100), 2.900 (90), 3.47 (80), 1.893 (30), 1.662 (30), 2.476 (25), 1.691 (20) Chemistry: TiO2 Fe2 O3 (1) 98.59 1.41 (2) 98.77 1.48

Total 100.00 100.25 (1) Snowdon, Wales; corresponds to (Ti0.99Fe0.01 )Σ=1.00 O2 . (2) Magnet Cove, Arkansas, USA; corresponds to (Ti0.99 Fe0.01 )Σ=1.00 O2 . Polymorphism & Series: Trimorphous with anatase and rutile.

Occurrence: An accessory mineral in alpineveins in gneiss and schist; in contact metamorphic zones and hydrothermal veinlets; a common detrital mineral. Association: Anatase, rutile, titanite, orthoclase, quartz, hematite, calcite, chlorite,muscovite.

Distribution: A widespread mineral, but only a few localities afford fine crystals. At Fron Oleu, near Tremadog, Gwynned, Wales. From Bourg d’Oisans, Is`re, France. In Switzerland, e in...