Anatase
General Information
Anatase is a polymorph with rutile and brookite. All three have the same chemistry, TiO2, but they have different structures. At higher temperatures, about 915 degrees celsius, anatase will automatically revert to the rutile structure. Rutile is the more common and the more well known mineral of the three, while anatase is the rarest. Anatase shares many of the same properties as rutile: luster, hardness, and density. However, due to structural differences, anatase and rutile differ slightly in crystal habit and cleavage.
Anatase and rutile have the same symmetry, tetragonal 4/m 2/m 2/m, despite having different structures. In Rutile, the structure is based on octahedrons of titanium oxide which share two edges of the octahedron with other octahedrons and form chains. It is the chains themselves which are arranged into a four-fold symmetry. In anatase, the octahedrons share four edges, hence the four fold axis.
Crystals of anatase are very distinctive and are not easily confused with any other mineral. They form the eight faced tetragonal dipyramids that come to sharp elongated points. The elongation is pronounced enough to distinguish this crystal from octahedral crystals, but there is a similarity.
Nice specimens of anatase are associated with quartz and are considered classics in the mineral world. The good luster, well formed crystal shape and interesting character make anatase a popular mineral for collectors
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Chemistry: TiO2, Titanium Oxide
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Class: Oxides and Hydroxides
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Subclass:
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Color: Brown to black; Yellow or Blue
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Streak: White |
Luster: Adamantine to Sub-Metallic
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Transparency: Opaque
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Crystal System: Tetragonal
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Hardness: 5.5-6
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Cleavage: Perfect in basal direction and in four directions; pyramidal
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Fracture: Subconchoidial
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Specific Gravity: 3.8-3.9
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Crystal Habits: Typical tetragonal dipyramids that come to sharp elongated terminations points
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Uses: Mineral specimens
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Associated Minerals: Brookite, Rutile, Quartz, Feldspars, Apatite, Hematite, Chlorite, Micas, Calcite, Sphene
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Other Characteristics: Crystals are easily altered in nature and sometimes pitted
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Notable Occurrences: Somerville, Massachusetts and Gunnison Co., Colorado, USA; Tavistock, Devon, England; Austria; Diamantina District, Brazil; French Alps; Binnatal area of Switzerland |
Best Field Indicators: Crystal habit, luster, cleavage, density, streak, associations, locality
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