Anatase is a minor ore of
titanium and the chemical form Titanium
Dioxide (TiO
2). It is a member of the
oxide class of
minerals. The oxide class is often black in color (but not always) and are very
abundant (45% of the Earth's crust by weight is composed of
oxygen).
Anatase is similar to the minerals rutile and brookite in chemical composition, however, they have different structures. Anatase is the rarest of the three. This rarity is possibly because at 915 degrees
Celsius, anatase reverts to the rutile structure.
Anatase is often a dark color (typically brown to black), however, there are specimens colored yellow and blue. Crystals of anatase are opaque and quite distinctive - they form eight faced tetragonal elongated dipyramids. (huh?) It looks like an octahedron (or 8-sided dice) that has been stretched. Because of this resemblance, it is often (mistakenly) called "octahedrite".
The hardness for anatase ranges from 5.5 to 6 on the Mohs hardness scale and has a specific gravity of 3.8 g/cm3 to 3.9 g/cm3 (which is average for metallic minerals).
Anatase is often found with the other titanium oxides along with quartz, feldspars, apatite, hematite, chlorite, micas, calcite, and sphene. The best places to look for anatase is in Massachusetts, Colorado, Devon (England), Austria, Brazil, and in the French Alps.
The name 'anatase' comes from the Greek word 'anatasis' for 'extension' or 'elongation' referring to the stretched nature of the faces compared to other tetragonal minerals.