|
| Formula | Ca(Mg,Fe)SiO4 |
| | Optic class & sign | Biaxial negative |
| | Optical orientation | X = b, Y = c, Z = a |
| | Optical plane | (001) |
| | Relief | Moderate-positive |
| | Refractive indices | nx = 1.638 -1.654
|
|
ny = 1.646 -1.664
|
|
nz = 1.650 -1.674
|
|
| n increases with increasing Fe, Mn |
| | Birefringence (max.) | 0.012 - 0.020 |
| | | Δn increases with increasing Fe, Mn |
| | Optic Angle
| 2Vx
= 69 - 88° |
| | 2Vz
|
| | Sign of elongation | Length-slow, l(+), length-fast, l(-) |
| | Interference figure | Few isochromes, high 2V, dispersion |
| | Colour / pleochroism | Colourless |
| | Zoning | |
|
|
| Form | Habit | Equant, short columnar, tabular, or irregular shapes |
| | | Surface | Commonly anhedral; if euhedral, cross-sections with 8 or more faces |
| | Cleavage | Poor |
| | Twinning | {031} cyclic: six-pointed star-shaped arrangement |
| | Extinction | Morphological elements against which extinction can be judged are commonly not developed |
|
|
| Reaction textures | Reaction rims on olivine or Ca-pyroxene |
| | Alteration / decomposition | Serpentine, tremolite |
|
|
| Occurence | Ign | Peridotite, carbonatite, lamprophyre, nepheline- or melilite-bearing rocks, kimberlite, alnöite |
| | | Met | High-temperature siliceous marble (from impure dolostone), typically at contacts with felsic, alkaline or basic intrusives; skarn |
| | | Sed | |
| | | Hyd | |
| | | Other | |
|
|
| Distinctive properties | Birefringence, optic sign, high 2V, poor cleavage |
| | Additional comments | Endmember kirschsteinite CaFeSiO4, with nz = 1.740 (not known to occur naturally) |
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