Anatase is one of the three
mineral forms of
titanium dioxide, the other two being
brookite and
rutile. It is always found as small, isolated and sharply developed
crystals, and like rutile, a more commonly occurring modification of titanium dioxide, it crystallizes in the
tetragonal system; but, although the degree of symmetry is the same for both, there is no relation between the interfacial angles of the two minerals, except, of course, in the prism-zone of 45° and 90°. The common pyramid of anatase, parallel to the faces of which there are perfect cleavages, has an angle over the polar edge of 82°9', the corresponding angle of rutile being 56°52½'. It was on account of this steeper pyramid of anatase that the mineral was named, by
RJ Haüy in
1801, from the
Greek anatasis, "extension," the vertical axis of the crystals being longer than in rutile. There are also important differences between the physical characters of anatase and rutile; the former is not quite so
hard (H=5½–6) or dense (
specific gravity 3.9); it is optically negative, rutile being positive; and its lustre is even more strongly
adamantine or metallic-adamantine than that of rutile.
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General Information:
Chemical Formula:
TiO2
Composition:
(Molecular Weight = 79.88 gm)
Titanium 59.94 %
TiOxygen 40.06 %
O Empirical Formula:
TiO2
IMA Status:
Accepted IMA 1980
Locality:
Minas Geraes, Brazil
Name Origin:
From the Greek, anatasis - "elongation."
Physical Properties:
Cleavage:
[101] Perfect, [001] Distinct
Color:
black, reddish brown, yellowish brown, dark blue, or gray.
Density:
3.9
Diaphaniety:
Transparent to translucent
Habits:
Pyramidal - Crystals are shaped like pyramids., Tabular - Form dimensions are thin in one direction.,
Hardness:
5.5-6 - Knife Blade-Orthoclase
Luminescence:
None.
Luster:
Adamantine - Resinous
Streak:
pale yellowish white
More details...
ANATASIO. OTTAEDRITE
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