Pseudobrookite

Pseudobrookite
Spray of pseudobrookite needles from Topaz Mountain in Utah (size: 2.7 × 2.0 × 1.6 cm)
General
CategoryOxide mineral
Formula
(repeating unit)		Fe2TiO5
IMA symbolPbrk[1]
Strunz classification4.CB.15
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupBbmm
Unit cella = 9.81 Å, b = 9.95 Å,
c = 3.73 Å; Z = 8
Identification
ColorDark reddish brown, brownish black, black
Crystal habitPrismatic to needle like, striated
CleavageDistinct on {010}
FractureUneven to subconchoidal
Mohs scale hardness6
LusterAdamantine, greasy, metallic
StreakBrown
DiaphaneityOpaque, transparent in thin splinters
Specific gravity4.33–4.39
Optical propertiesBiaxial (+)
Refractive indexnα = 2.350 nβ = 2.390 nγ = 2.420
Birefringenceδ = 0.070
2V angleMeasured: 50°
References[2][3][4]

Pseudobrookite is an iron titanium oxide mineral with formula: Fe2TiO5[2] or (Fe3+,Fe2+)2(Ti,Fe2+)O5.[3]

Discovery and occurrence

Pseudobrookite was first described in 1878 for an occurrence in Uroi Hill (Arany Hill), Simeria, Hunedoara County, Romania. The name is from Greek ψευδής, for false, and brookite because of its misleading similar appearance to brookite.[2]

Pseudobrookite forms as pneumatolytic deposition and alteration within titanium-rich volcanic rocks such as andesite, rhyolite or basalt. It may be associated with xenoliths contained in the volcanics. It also commonly occurs in lithophysae.[4]

It occurs associated with hematite, magnetite, bixbyite, ilmenite, enstatite-ferrosilite, tridymite, quartz, sanidine, topaz, spessartine, beryl, mica, cassiterite and apatite.[4]

Occurrences include:[4]

References

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c Pseudobrookite on Mindat.org
  3. ^ a b Pseudobrookite on Webmin
  4. ^ a b c d Handbook of Mineralogy