Anatase is usually found in very small crystals, seldom transparent, and even then very dark-colored. Gems have been cut as curiosities, but are almost never seen for sale on the market because of scarcity.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Alternate Common Names||Octahedrite See: Brookite, Rutile|
|Crystallography||Tetragonal; crystals pyramidal, striated; also tabular and prismatic.|
|Colors||Black, red-brown, brown, deep indigo-blue; colorless to grayish, greenish, blue-green, lavender, Banding due to zonal growth often visible.|
|Luster||Adamantine, sometimes slightly metallic.|
|Birefringence||0.046 – 0.067|
|Cleavage||Perfect 2 directions. Fracture subconchoidal. Brittle|
|Dispersion||0.213 (o); 0.259 (e)|
|Stone Sizes||Faceted gems are exceedingly rare and always very small (less than 1-2 carats). Usually the material is very dark and unappealing. Cut gems are known as large as ~6 carats.|
|Pleochroism||Strong in deeply colored crystals: brown/yellow-brown/greenish-blue.|
Optics: o= 2.534 – 2.564; e = 2.488-2.497
Refractive indices are extremely variable, depending on temperature and wavelength. Anastase is sometimes biaxial with small 2V (dark-colored crystals).
Occurrence: Gneisses, schists, and other metamorphic rocks; as detrital grains, as an accessory mineral in granites, and in various other igneous rocks.
California: Gunnison County, Colorado; Arkansas; Massachusetts; Virginia; North Carolina.
Canada; Brazil; Cornwall, England; Wales; Norway; France; Italy; USSR.
Switzerland: gem material from the Alpine regions.
Brazil: found in diamondiferous gravels.
Comments: Anatase is usually found in very small crystals, seldom transparent, and even then very dark-colored. Gems have been cut as curiosities, but are almost never seen for sale on the market because of scarcity.
Name: Greek anatasis, meaning erection because the “octahedron” of Anatase is really a tetragonal bipyramid and elongated with respect to the octahedron of the isometric system.