PSEUDOBROOKITE

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Orthorhombic
    Chemistry : Fe2TiO5
    Rarity : Uncommon

Pseudobrookite is an oxide of pneumatolytic origin from acidic to basic titaniferous lavas (rhyolites to basalts), which can also crystallize by reaction with the xenolites embedded in them; it frequently accompanies tridymite, sanidine and apatite. It is a mineral which is also commonly of fumarolic origin. Its name comes from the Greek pseudês (false) and brookite, because we observe a chemical relationship between these two minerals. Pseudobrookite forms crystals of varied habitus, acicular to equant, sometimes curved, ordinarily millimeters commonly united in radiated aggregates. Its color is black to dark reddish brown.

Main photo : Pseudobrookite from Petit Chambois, Mazaye, Puy-de-Dôme, France © Yannick Vessely

Pseudobrookite from Topaz Mountain, Thomas Range, Utah, USA © Bruce Kelley
Pseudobrookite from Uroi Hill, Romania © Vincent Bourgoin
Pseudobrookite from Mt Calvario, Sicily, Italy © Nazareno La Manna
Pseudobrookite from Petit Chambois, Puy-de-Dôme, France © Pascale & Daniel Journet

Pseudobrookite in the World

The most beautiful pseudobrookite crystals come from bixbyite and topaz lithophyses of the rhyolites of Topaz Mountain (Utah) and hypersthene basalt geodes of the Crater Lake district (Oregon), they measure up to 2 cm. The Uroi volcano in the province of Alba (Romania) also produced beautiful crystals but of smaller size. Fumarollic pseudobrookite is quite common and known in the Azores, Kilimanjaro (Tanzania) and Vesuvius (Italy).

Pseudobrookite in France

In France, pseudobrookite is known in the trachyte and andesite geodes of Mont-Dore and in the basalts of the Chaîne des Puys such as at the Lemptégy volcano, at Petit Chambois or at Puy de Tunisset (Puy-de-Dôme). It is also known on the volcanoes of Haute-Loire and Cantal, as well as in Reunion.

Twinning

Twins would sometimes be present but not listed...

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 6
Density : 4.33 to 4.39
Fracture : Irregular to sub-conchoidal
Streak : Red-brown to yellow

TP : Transparent to opaque
RI : 2,350 to 2,420
Birefringence : 0.030 to 0.040
Optical character : Biaxial +
Pleochroism : Low
Fluorescence : None

Solubility : Hydrochloric acid, sulfuric acid

Magnetism : NoneRadioactivity : None

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