Anatase

anatase

ilmenite

brookite

Images

Formula: TiO₂
Simple oxide, paramorph of brookite and rutile.
Crystal System: Tetragonal
Specific gravity: 3.79 to 3.97 measured, 3.89 calculated
Hardness: 5½ to 6
Streak: White to pale yellow
Colour: Brown, pale yellow or reddish brown, indigo, black; pale green, pale lilac, grey, rarely nearly colourless; brown, yellow-brown, pale green, blue in transmitted light.
Solubility: Insoluble in acids (Dana)
Common impurities: Fe,Sn,V,Nb
Environments:

Igneous environments
Pegmatites
Carbonatites
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Anatase is usually secondary, derived from other titanium-bearing minerals. In Alpine veins it is derived from the enclosing gneiss or schist by leaching by hydrothermal solutions. In also occurs in igneous and metamorphic rocks, in pegmatites and carbonatites. It is a common detrital mineral (HOM, Dana). Common associates include brookite, rutile, titanite, ilmenite, titanium-rich magnetite, hematite, quartz, adularia and chlorite (HOM, Mindat, Dana).

Localities

At the Mount Lyell Mines, Queenstown district, West Coast municipality, Tasmania, Australia, anatase is common in many disseminated ores and schistose wallrocks. Well formed crystals to 1 mm have been found on quartz crystals with abundant hematite inclusions (AJM 21.2.21).

At the Marcil quarry, near Ste-Clotilde-de-Châteauguay, Quebec, Canada, anatase has been found associated with quartz and dolomite. The mineral is formed early in the paragenetic sequence, appearing to have preceded quartz (R&M 86.6.549).

At the type locality, St Christophe-en-Oisans, Auvergne-Rhône-Alpes, France, anatase occurs in Alpine veins, derived from the enclosing gneiss or schist by hydrothermal solutions (Mindat).

At Johanngeorgenstadt, Erzgebirgskreis, Saxony, Germany, Grey-blue, simple tetragonal-bipyramidal crystals of anatase with a metallic to glassy lustre, grown in and on quartz and associated with the tin-tungsten formation, have been described. Blue-grey to black bipyramids of anatase lining fissures in gneiss at the Schaar shaft have also been reported (MinRec 55.5.587).

At the Monte Cervandone area, Devero Alp, Baceno, Verbano-Cusio-Ossola Province, Piedmont, Italy, very good anatase specimens have come from near the peak of Monte Cervandone. The first finds of these were made in the early 1950s; the anatase crystals, probably found in gneiss clefts, are sharp and prismatic with several bipyramidal forms, and reach 8 mm. In more recent times, very near the same site, spectacular anatase crystals to 3 cm were discovered. Two generations of an unusual niobium-rich anatase have been found sporadically in clefts around the Wannigletscher. The first-generation crystals are black platelets to 1 cm; second-generation crystals are smaller and bright yellow-orange (MinRec 56.3.296-297).
Anatase from the Monte Cervandone area - Image

At the the Santo Nino Mine, Santa Cruz County, Arizona, USA, anatase occurs in association with quartz, muscovite, sericite and adularia (R&M 87.2.126).

At Placerville, California, USA, anatase occurs with brookite on quartz (Dana).

At Quincy, Massachusetts, USA, anatase occurs in pockets in a pegmatite with aegirine, fluorite and ilmenite (Dana).
Anatase from Quincy - Image

Near dolerite dikes at Somerville, Massachusetts, USA, anatase occurs with brookite and titanite (Dana).
Anatase from Somerville - Image

At Arvon, Buckingham county, Virginia, USA, anatase is found in joint planes in slate with quartz and pyrite (Dana).

Stability

The PT diagram below illustrates that rutile is stable at a higher temperature than anatase ( Journal of Materials Science, 46.855–874).























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