| General Formula: CaTiOSiO4 |
Sample: 88-18 | System: Monoclinic |
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| Sphene Note the high relief of the sphene grain compared to the other minerals in the field of view. Field of view = 2.7 mm, plane light |
Sphene Note the high interference colour, of the sphene, which may be masked by the colour of the grain. Field of view 2.7 mm, crossed polars |
Block diagram showing the relationship between the crystallographic axes and the indicatrix axes. |
Optical Properties
| Colour Pleochroism |
shades of brown, less commonly colourless or yellow non to weakly pleochroic |
Form | euhedral to subhedral grains with a wedge or diamond shaped cross section |
| Relief RI |
very high positive nalpha = 1.843-1.950 nbeta = 1.870-2.034 ngamma = 1.943-2.110 |
Cleavage | good prismatic cleavage {110}, but not usually obvious in thin section |
| Birefringence Interference Colours |
0.100-0.192 extreme birefringince produces upper order white/cream interference colours |
Twinning | simple twins on {100} and lamellar twins on {221} |
| Interference Figure Optic Sign 2V |
biaxial positive 2VZ = 17-40° |
Optic Orientation | X ^ a =-6 to -21 ° Y = b Z ^ c = +35 to 51° optic plane = (010) |
| Composition | Al3+ and Fe3+ may substitute for Ti4+, a wide variety of other cations, e.g. REE, U and Th, may substitute for Ti. |
Alteration | alters to leucoxene |
| Occurrence | a common accessory in a wide variety of igneous and metamorphic rocks. | Distinguishing Features | very high relief and extreme birefringence |
