Crystal Chemical Properties: Anatase is polymorphic with rutile and brookite, meaning it has the same composition but different crystal structures. Anatase belongs to the tetragonal crystal system, with an approximately framework-like crystal structure. O ions are in cubic close-packed formation, and Ti atoms are located in octahedral interstices. The [TiO6] octahedra are interconnected by two pairs of opposing edges, forming a helical chain parallel to the c-axis around each fourth helical axis. The coordination number of Ti is 6, and the coordination number of O is 3. The interatomic spacing between Ti and O atoms is 0.1937 nm and 0.1964 nm, and the interatomic spacing between O and O atoms is 0.2802 nm and 0.3040 nm.
Chemical Properties: Anatase has the same chemical composition as rutile, with the chemical formula TiO2, and it isomorphously substitutes for Fe, Sn, Nb, Ta, etc. Furthermore, rare earth elements, mainly group Y, as well as U and Th, have been found in anatase. Physical Properties: Crystal forms are generally conical, tabular, or columnar. Colors include brown, yellow, light greenish-blue, light purple, and grayish-black, occasionally nearly colorless. Streak is colorless to pale yellow. It has an adamantine luster. Cleavage is perfect. Mohs hardness is 5.5–6.5. Density is 3.82–3.976 g/cm³.
Optical Properties: In thin sections, it exhibits various colors, mainly brown, yellow, light greenish-blue, light purple, and grayish-black, occasionally nearly colorless. It is a uniaxial crystal (negative optical property), sometimes a biaxial crystal with a small optic axis angle. The refractive index is very high and varies significantly; for example, yellow crystals have a refractive index of n0 = 2.501, while gray crystals have n0 = 2.556. Pleochroism is weak; darker crystals have stronger pleochroism. Strong wine-yellow crystals have no: dark wine-yellow, ne: light reddish-brown. In a light film under reflected light, anatase appears gray with obvious internal reflection, a bluish tint, no birefringence or pleochroism, and a slightly higher reflectivity than zinc sphalerite.
