anatase

{{Infobox mineral | name = Anatase | category = Oxide minerals | boxwidth = | boxbgcolor =#4c6794 | boxtextcolor = #fff | image = Anatase Oisans.jpg | alt = | caption = | formula = TiO2 |IMAsymbol=Ant | molweight = 79.88 g/mol | strunz = 4.DD.05 | system = Tetragonal | class = Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) | symmetry = I41/amd | unit cell = a = 3.7845, c = 9.5143 [Å]; Z = 4 | color = Black, reddish to yellowish brown, dark blue, gray | habit = Pyramidal (crystals are shaped like pyramids), tabular (form dimensions are thin in one direction). | twinning = Rare on {112} | cleavage = Perfect on [001] and [011] | fracture = Subconchoidal | tenacity = Brittle | mohs = 5.5–6 | luster = Adamantine to splendent, metallic | refractive = nω = 2.561, nε = 2.488 | opticalprop = Uniaxial (−), anomalously biaxial in deeply colored crystals | birefringence = δ = 0.073 | pleochroism = Weak | streak = Pale yellowish white | gravity = 3.79–3.97 | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to nearly opaque | other = | references = }}

Anatase is a metastable mineral form of titanium dioxide (TiO2) with a tetragonal crystal structure. Although colorless or white when pure, anatase in nature is usually a black solid due to impurities. Three other polymorphs (or mineral forms) of titanium dioxide are known to occur naturally: brookite, akaogiite, and rutile, with rutile being the most common and most stable of the bunch. Anatase is formed at relatively low temperatures and found in minor concentrations in igneous and metamorphic rocks. Glass coated with a thin film of TiO2 shows antifogging and self-cleaning properties under ultraviolet radiation.