ClassicGems.net

Anatase

Discovered in 1801;   IMA status:  Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

TiO₂

Titanium Oxide

Molecular Weight:

79.88 gm

Composition:

Titanium

59.94 %

Ti

100.00 %

TiO₂

Oxygen

40.06 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/D.14-10

Nickel-Strunz 10th Ed. ID:

4.DD.05

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
D : Metal: Oxygen = 1:2 and similar
D : With medium-sized cations; frameworks of edge-sharing octahedra

Related to:

None

Members of Group:

None

Varieties:

Gel-Anatase, Niobian Anatase

Synonyms:

Dauphinite, Hydrotitanite, Octaèdrite, Octahedrite, Oisanite, Schorl bleu indigo, Schorl octaedre rectanglaire, Wiserine, Xanthotitane

Crystal Data

Crystallography:

Tetragonal - Ditetragonal Dipyramidal

Crystal Habit:

Crystals typically acute dipyramidal, often highly modified; obtuse pyramidal or tabular; less commonly prismatic, to 3.75 cm.

Twinning:

Rare on {112}

Physical Properties

Cleavage:

Perfect on {001} and {011}

Fracture:

Sub-Conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.0; VHN = 616–698 (100 g load)

Density:

3.82 - 3.97 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Brown, pale Yellow or Reddish Brown, Indigo, Black; pale Green, pale Lilac, Gray, rarely nearly Colorless; Brown, Yellow-Brown, pale Green, Blue in transmitted light.

Transparency:

Transparent when light colored, to nearly opaque when deeply colored. Pyramidal crystals may appear opaque because of total reflection.

Luster:

Adamantine to Splendent, Metallic

Refractive Index:

2.488 - 2.564 (very high)  Uniaxial ( - ) anomalously biaxial in deeply colored crystals

Birefringence:

0.046 - 0.067

Dispersion:

0.213 - 0.259 (very high)

Pleochroism:

Weak; stronger in deeply colored crystals

Occurances

Geological Setting:

Usually secondary, derived from other titanium-bearing minerals. In Alpine veins, derived from the enclosing gneisses or schists by hydrothermal solutions. In igneous and metamorphic rocks; in pegmatites; from a carbonatite. A common detrital mineral.

Common Associations:

Brookite, Rutile, Titanite, Ilmenite, Titanian Magnetite, Hematite, Quartz.

Common Impurities:

Fe, Sn, V, Nb

Type Locality:

St. Christophe-en-Oisans, Bourg d'Oisans, Isère, Rhône-Alpes, France

Year Discovered:

1801

View mineral photos:

Anatase Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Anatase is an extremely rare gem mainly because crystals are usually very dark, seldom transparent and small. Anatase has very high dispersion and RI, but its dark color usually masks these. Lighter colored gems are quite bright and beautiful and among the rarest of all gems. Anatase is one of the three forms of Titanium Dioxide found as gemstones. The other two are Brookite and Rutile. This means that the three minerals have the same chemistry, TiO2, but they have different structures.

Anatase is named from the Greek word anatasis, meaning extension referring to the length of the pyradimal faces of crystals being longer in relation to their bases than in many other Tetragonal minerals.

Anatase is a very wide-spread mineral, however only a few occurrences can be noted. In Alpine veins at many localities throughout the Swiss, French, and Italian and Tirolian Alps: large crystals from Binn, Valais, and at Cavradi, Tavetsch, Graubünden, Switzerland. From LaGrave, Hautes-Alpes, and Bourg d’Oisans, Isère, France. In Norway, at Kragerø; fine crystals from Hardangervidda, Ullensvang; Slidre, Valdres; and Gudbrandsdalen. From the Khodrovy Mountains, Sakha, Russia. In the Virtuous Lady mine, Devonshire, England. At Fron Oleu, near Tremadog, Gwynned, Wales. In several carbonatite deposits, aggregating 500 million tons, in Minas Gerais and Pará, Brazil. In the USA, at many localities in Burke County, North Carolina; Buckingham County, Virginia; from Quincy, Norfolk County, Massachusetts; at Placerville, Eldorado County, California. In Canada, at Sherbrooke Township, Nova Scotia, and in Henvey Township, Ontario.

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