THE MINERAL ANATASE
- Chemical Formula: TiO2, Titanium Oxide
- Class: Oxides and Hydroxides
- Uses: A very minor ore of titanium and as mineral specimens.
Anatase is a polymorph with two other minerals.
The minerals rutile
as well as anatase all 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 or nearly the same properties as
rutile such as luster, hardness and density.
However due to structural differences anatase and rutile differ
slightly in crystal habit and more distinctly in 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
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
form from octahedral crystals, but there is a similarity.
In fact anatase is wrongly called "octahedrite"
in spite of the difference in forms.
Of course "tetragonal dipyramidite" does not sound right either!
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.
- Color is brown to black, also yellow and blue.
- Luster is adamantine to submetallic.
- Transparency crystals are opaque.
- Crystal System is tetragonal; 4/m 2/m 2/m
- Crystal Habits include the typical tetragonal dipyramids
that come to sharp elongated terminations points.
These crystals look like stretched out octahedrons.
- Cleavage is perfect in the basal direction and in four directions, pyramidal.
- Fracture is subconchoidal.
- Hardness is 5.5 - 6
- Specific Gravity is 3.8 - 3.9 (average for metallic minerals)
- Streak is white.
- Other Characteristics: Crystals are easily altered in
nature and sometimes pitted.
- Associated Minerals include
- Notable Occurrences include Somerville, Massachusetts and
Gunnison Co., Colorado, USA; Tavistock, Devon, England; Austria;
Diamantina District, Brazil; in the French Alps
and at the Binnatal area of Switzerland.
- Best Field Indicators are crystal habit,
luster, cleavage, density, streak, associations and locality.