Rutile structure
| Rutile | |
|---|---|
 |
|
| General | |
| Category | Oxide minerals |
|
Formula (repeating unit) |
TiO2 |
| Strunz classification | 4.DB.05 |
| Crystal system | Tetragonal |
| Crystal class | Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) |
| Space group | P42/mnm |
| Unit cell | a = 4.5937, c = 2.9587 [Å]; Z = 2 |
| Identification | |
| Color | Reddish brown, red, pale yellow, pale blue, violet, rarely grass-green; black if high in Nb–Ta |
| Crystal habit |
Acicular to Prismatic crystals, elongated and striated parallel to [001] |
| Twinning | Common on {011}, or {031}; as contact twins with two, six, or eight individuals, cyclic, polysynthetic |
| Cleavage | {110} good, 100 moderate, parting on {092} and {011} |
| Fracture | Uneven to sub-conchoidal |
| Mohs scale hardness | 6.0 – 6.5 |
| Luster | Adamantine to submetallic |
| Streak | Bright red to dark red |
| Diaphaneity | Opaque, transparent in thin fragments |
| Specific gravity | 4.23 increasing with Nb–Ta content |
| Optical properties | Uniaxial (+) |
| Refractive index | nω = 2.613 nε = 2.909 (589nm) |
| Birefringence | 0.296 (589nm) |
| Pleochroism | Weak to distinct brownish red-green-yellow |
| Dispersion | strong |
| Fusibility | Fusible in alkali carbonates |
| Solubility | Insoluble in acids |
| Common impurities | Fe, Nb, Ta |
| References | |
Acicular to Prismatic crystals, elongated and
Rutile is a mineral composed primarily of titanium dioxide, Ti O2.
Rutile is the most common natural form of TiO2. Three rarer polymorphs of TiO2 are known:
Rutile has among the highest refractive indices at visible wavelengths of any known crystal, and also exhibits a particularly large birefringence and high dispersion. Owing to these properties, it is useful for the manufacture of certain optical elements, especially polarization optics, for longer visible and infrared wavelengths up to about 4.5μm.
Natural rutile may contain up to 10% iron and significant amounts of niobium and tantalum. Rutile derives its name from the Latin rutilus, red, in reference to the deep red color observed in some specimens when viewed by transmitted light.
Rutile is a common accessory mineral in high-temperature and high-pressure metamorphic rocks and in igneous rocks.
Thermodynamically, rutile is the most stable polymorph of TiO2 at all temperatures, exhibiting lower total free energy than metastable phases of anatase or brookite. Consequently, the transformation of the metastable TiO2 polymorphs to rutile is irreversible. As it has the lowest molecular volume of the three main polymorphs; it is generally the primary titanium bearing phase in most high-pressure metamorphic rocks, chiefly eclogites.
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Wikipedia