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A.K.A. Sphene |
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Formula | CaTiOSiO4 | |
Crystal System | Monoclinic (2/m) | Beta = 119.9° |
Crystal Habit | Wedge-, and elongated rhomb-shaped crystals are common, but rounded and irregular grains are also common. Grains typically are not apparent in hand specimens. | Diamond-shaped cross-sections can be seen in thin sections. Titanite has very high positive relief. H=5-51/2 |
Cleavage | Distinct prismatic ceavage {110} may control grain orientation. Uneven fracture. Brittle. | Partings parallel to twins may be more prominent than
cleavage. |
Twinning | Simple twins may occur on {100}. | |
Color/Pleochroism | Tan-brown or yellowish color. Nonpleochroic to weakly pleochroic: x
almost colorless |
Color appears the same in plane- and crossed polarized light. |
Optic Sign | Biaxial (+) | |
2V | 20-40° | |
Optic Orientation | X /\ a=-6° to -21° |
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Refractive
Indices alpha = beta = gamma = |
1.843-1.950 1.970-2.034 1.943-2.110 |
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Max Birefringence | 0.100-0.192 | Birefringence is high order white or beige (like calcite) with little variation when the stage is rotated. |
Elongation | cannot be easily determined | |
Extinction | Because of high dispersion, some grains do not extinguish completely. | |
Dispersion | r > v | Optic axis dispersion is very strong, inclined dispersion in weak. |
Distinguishing Features | Very High Relief. Extreme birefringence; same brownish color in plane and crossed polars. Diamond/wedge-shaped crystal habit | |
Occurrence | Titanite is a common accessory in many igneous and metamorphic rocks, of which it can be the dominent Ti-bearing contituent. Titanite also occrs as detrital grains in the heavy mineral fraction of clastic sediments. | |
Editors | Sarah Pistone ('06), Janelle McAtamney ('07), Molly Peek ('18) | |
Sources | Philpotts, Anthony R., 1989. Petrogrophy of Igneous
and Metamorphic Rocks. Waveland Press, Inc.: Prospect Heights,
Illinois.
61 p. |