Pseudobrookite

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

Pseudobrookite
Spray of pseudobrookite needles from Topaz Mountain in Utah (size: 2.7 × 2.0 × 1.6 cm)
General
Category	Oxide mineral
Formula	Fe2TiO5
IMA symbol	Pbrk[1]
Strunz classification	4.CB.15
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Bbmm
Unit cell	a = 9.81 Å, b = 9.95 Å, c = 3.73 Å; Z = 8
Identification
Color	Dark reddish brown, brownish black, black
Crystal habit	Prismatic to needle like, striated
Cleavage	Distinct on {010}
Fracture	Uneven to subconchoidal
Mohs scale hardness	6
Luster	Adamantine, greasy, metallic
Streak	Brown
Diaphaneity	Opaque, transparent in thin splinters
Specific gravity	4.33–4.39
Optical properties	Biaxial (+)
Refractive index	nα = 2.350 nβ = 2.390 nγ = 2.420
Birefringence	δ = 0.070
2V angle	Measured: 50°
References	[2][3][4]

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]

• Mayen in the Eifel district, Germany
• Mont Dore, Puy-de-Dome, France
• Vesuvius, Italy
• Jumilla, Murcia Province, Spain
• Faial and São Miguel Islands, Azores
• Kilimanjaro, Tanzania;
• Reunion Island
• the Thomas Range, Juab County, Utah
• Crater Lake and Lemolo Lake, Oregon
• the Black Range, Sierra County, New Mexico
• Cerro los Remedios, Durango, Mexico