Brookite
Image: Nessa Eull (CC0)
Mineral NameBrookite
Chemical FormulaTiO2
Mohs Hardness5.5
Crystal Systemorthorhombic
Lustervitreous
Streak Coloryellowish-brown to black, or colorless
Cleavagedistinct on {120}, indistinct on {001}
Fracturesubconchoidal to irregular
Specific Gravity4.08
Colorsreddish-brown, dark brown, black, yellowish, blue
Transparencyopaque to translucent
Type LocalityMagnet Cove, Hot Spring County, Arkansas, USA
Mineral GroupOxides
Usescollector's mineral, minor source of titanium
Associated Mineralsrutile, anatase, quartz, adularia, chlorite
Rarityuncommon
Description
Brookite forms dark, tabular to platy crystals, often exhibiting a submetallic to adamantine luster. It is a polymorph of rutile and anatase, sharing the same chemical composition.
Geological Context
Brookite typically forms in hydrothermal veins, alpine clefts, or as an alteration product in metamorphic and igneous rocks, stable at lower temperatures than its polymorph rutile.
