|
| Formula | (Mn,Ca,Fe)SiO3 |
| | Optic class & sign | Biaxial negative |
| | Optical orientation | X near c, Y near a, Z near b |
| | Optical plane | Oblique to a, b, c; at a high angle to (001) |
| | Relief | Moderate to high |
| | Refractive indices | nx = 1.640 -1.695
|
|
ny = 1.651 -1.708
|
|
nz = 1.653 -1.710
|
|
| n increases with increasing Mn and Fe |
| | Birefringence (max.) | 0.013 - 0.017 |
| | | Δn shows only minor variation with composition |
| | Optic Angle
| 2Vx
= 34 - 60° |
| | 2Vz
|
| | Sign of elongation | Length-slow, l (+) |
| | Interference figure | Sections at a high angle to c show acute bisectrix figures, if 2V is relatively small; only first-order isochromes |
| | Colour / pleochroism | Colourless to pale orange or pink; weak pleochroism
|
| | Zoning | - |
|
|
| Form | Habit | Tabular, prismatic, fibrous, granular |
| | | Surface | Euhedral to anhedral |
| | Cleavage | {100}, {001} |
| | Twinning | Simple on {110}, uncommon |
| | Extinction | Inclined to all morphological elements; max extinction b∧Z (incl traces of {100} faces and cleavage) = 35° |
|
|
| Reaction textures | |
| | Alteration / decomposition | |
|
|
| Occurence | Ign | |
| | | Met | Metasomatic Mn deposits, manganiferous skarn |
| | | Sed | |
| | | Hyd | |
| | | Other | |
|
|
| Distinctive properties | Low birefringence, relief, triclinic symmetry |
| | Additional comments | n-Δn data plotted here have been taken from Deer, Howie & Zussman (1997) |
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