Brookite

Brookite
Brookite
	Brookite from Balochistan
General
Category	Oxide minerals
Formula; (repeating unit)	TiO2
Strunz classification	4.DD.10 (10 ed) ; 4/D.15-10 (8 ed)
Dana classification	4.4.5.1
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) ; H-M symbol: (2/m 2/m 2/m)
Space group	Pbca
Unit cell	a = 5.4558 Å, ; b = 9.1819 Å, ; c = 5.1429 Å; Z = 8
Identification
Formula mass	79.88 g/mol
Color	Deep red, reddish brown, yellowish brown, brown, or black
Crystal habit	Tabular and striated, pyramidal or pseudohexagonal
Twinning	On {120}, uncertain
Cleavage	Poor on {120}, in traces on {001}
Fracture	Subconchoidal to irregular
Tenacity	Brittle
Mohs scale hardness	5+1⁄2 to 6
Luster	Submetallic
Streak	White, greyish or yellowish
Diaphaneity	Opaque to translucent
Specific gravity	4.08 to 4.18
Optical properties	Biaxial (+)
Refractive index	nα = 2.583 nβ = 2.584 nγ = 2.700
Birefringence	δ = 0.117
Pleochroism	Very weak, yellowish, reddish, orange to brown
2V angle	Calculated: 12° to 20°
Dispersion	0.131 (compare to diamond at 0.044)
Ultraviolet fluorescence	Non-fluorescent
References

Brookite is the orthorhombic variant of titanium dioxide (TiO₂), which occurs in four known natural polymorphic forms (minerals with the same composition but different structure). The other three of these forms are akaogiite (monoclinic), anatase (tetragonal) and rutile (tetragonal). Brookite is rare compared to anatase and rutile and, like these forms, it exhibits photocatalytic activity.^[5] Brookite also has a larger cell volume than either anatase or rutile, with 8 TiO₂ groups per unit cell, compared with 4 for anatase and 2 for rutile.^[6] Iron (Fe), tantalum (Ta) and niobium (Nb) are common impurities in brookite.^[3]

Brookite was named in 1825 by French mineralogist Armand Lévy^[3] for Henry James Brooke (1771–1857), an English crystallographer, mineralogist and wool trader.^[1]

Arkansite is a variety of brookite from Magnet Cove, Arkansas, US. It is also found in the Murun Massif on the Olyokma-Chara Plateau of Eastern Siberia, Russia, part of the Aldan Shield.^[7]

At temperatures above about 750 °C, brookite will revert to the rutile structure.^[8]

^ ^a ^b ^c Brookite. Webmineral.com. Retrieved on 2011-10-14.
^ Gaines et al (1997) Dana’s New Mineralogy Eighth Edition. Wiley
^ ^a ^b ^c Brookite. Mindat.org (2011-09-17). Retrieved on 2011-10-14.
^ Brookite. Handbook of Mineralogy. (PDF) . Retrieved on 2011-10-14.
^ Di Paola, A; Addamo, M.; Bellardita, M.; Cazzanelli, E.; Palmisano, L. (2007). "Preparation of photocatalytic brookite thin films". Thin Solid Films. 515 (7–8): 3527–3529. Bibcode:2007TSF...515.3527D. doi:10.1016/j.tsf.2006.10.114.
^ Anatase and Brookite Archived 2012-03-17 at the Wayback Machine. Wikis.lib.ncsu.edu (2007-05-08). Retrieved on 2011-10-14.
^ Arkansite on Mindat
^ Brookite (Titanium Oxide). Galleries.com. Retrieved on 2011-10-14.

[Webmin-1] Brookite. Webmineral.com. Retrieved on 2011-10-14.

[Dana-2] Gaines et al (1997) Dana’s New Mineralogy Eighth Edition. Wiley

[Mindat-3] Brookite. Mindat.org (2011-09-17). Retrieved on 2011-10-14.

[HOM-4] Brookite. Handbook of Mineralogy. (PDF) . Retrieved on 2011-10-14.

[Brookite_Photocatalysis-5] Di Paola, A; Addamo, M.; Bellardita, M.; Cazzanelli, E.; Palmisano, L. (2007). "Preparation of photocatalytic brookite thin films". Thin Solid Films. 515 (7–8): 3527–3529. Bibcode:2007TSF...515.3527D. doi:10.1016/j.tsf.2006.10.114.

[ncsu-6] Anatase and Brookite Archived 2012-03-17 at the Wayback Machine. Wikis.lib.ncsu.edu (2007-05-08). Retrieved on 2011-10-14.

[7] Arkansite on Mindat

[amethyst-8] Brookite (Titanium Oxide). Galleries.com. Retrieved on 2011-10-14.

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