Anatase
Anatase is a mineral form of titanium dioxide (TiO2). It is one of three naturally occurring polymorphs of titanium dioxide, the others being rutile and brookite. Anatase is metastable and will transform to rutile upon heating.
Properties:
- Chemical Formula: TiO2 (Titanium Dioxide)
- Crystal System: Tetragonal
- Habit: Typically occurs as acute pyramidal crystals or as coatings. Can also be granular or massive.
- Color: Varies, often blue, yellow, brown, or black. Also colorless and white.
- Streak: White
- Luster: Adamantine to submetallic
- Diaphaneity: Transparent to opaque
- Mohs Hardness: 5.5 - 6.0
- Specific Gravity: 3.82 - 3.97
- Cleavage: Perfect on {001}
- Fracture: Subconchoidal to uneven
- Refractive Index: Very high (2.488 - 2.561)
- Birefringence: 0.073
- Optical Orientation: Uniaxial (+)
- Dispersion: Very strong
Occurrence:
Anatase is found as an accessory mineral in metamorphic and igneous rocks. It is also found in veins, cavities, and alluvial deposits. Notable occurrences include Brazil, Norway, France, and the United States. It often occurs in association with other titanium minerals like rutile and ilmenite, as well as quartz, hematite, and feldspar.
Uses:
Due to its high refractive index and semiconducting properties, anatase (in its synthetic form, often as nanoparticles) has a number of industrial applications:
- Pigment: Used as a white pigment in paints, plastics, and paper, although rutile is more commonly used for this purpose due to its greater stability.
- Photocatalyst: Anatase is an effective photocatalyst, used in applications such as air and water purification, self-cleaning surfaces, and solar cells.
- UV Absorber: Used in sunscreens and cosmetics to absorb ultraviolet radiation.
- Semiconductor Applications: Research is ongoing regarding the use of anatase in various electronic devices.
Distinguishing Features:
Anatase can be distinguished from rutile by its crystal habit (typically more acute pyramidal), lower hardness, and optical properties. Brookite is generally orthorhombic, whereas anatase is tetragonal. The transformation to rutile upon heating is also a characteristic feature.