Anatase Locality : St Christophe-en-Oisans, Bourg d'Oisans, Isère, Rhône-Alpes, France - Topotype deposit Size :1.7 × 1.7 cm — Photo: Didier Descouens · CC BY-SA 4.0
Anatase
Also known as: Octahedrite.
A metastable form of titanium dioxide; pure crystals are colorless but natural anatase is usually blackened by impurities.
Intro adapted from Wikipedia (CC BY-SA).
Anatase is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula TiO₂.
It crystallizes in the tetragonal crystal system (space group I4_1/amd).
Key properties: Mohs hardness 5.5–6; specific gravity 3.79–3.97; typically brown or blue or black or yellow; White to pale yellow streak; Adamantine to splendent, metallic luster; refractive index 2.525; optically uniaxial.
IMA symbol Ant, IMA status: approved, named in 1801.
Usually secondary, derived from other titanium-bearing minerals. In Alpine veins, derived from the enclosing gneisses or schists by hydrothermal solutions. In igneous and metamorphic rocks; in pegmatites; from a carbonatite.
It is found associated with Brookite, rutile, titanite, ilmenite, titanian magnetite, hematite, quartz.
Its name comes from the Greek meaning extension, for the greater length of the usual pyramid compared with other tetragonal minerals.
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