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| Formula | Mg(Al,Fe3+)3(SiO4)2O(OH)
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| | Optic class & sign | Biaxial positive |
| | Optical orientation | X near a, Y = b, Z near c |
| | Optical plane | (010) |
| | Relief | High |
| | Refractive indices | nx = 1.689 -1.691
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|
ny = 1.691 -1.693
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nz = 1.712 -1.715
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| |
| | Birefringence (max.) | 0.023 - 0.024 |
| | | |
| | Optic Angle
| 2Vx
|
| | 2Vz
= 25 - 30° |
| | Sign of elongation | Length-slow, l (+) in sections close to (001) and (010); length-fast, l (-) in sections near (100). Y is parallel to the long dimension of the crystals. |
| | Interference figure | |
| | Colour / pleochroism | X: pale blue or green, Y: indigo, Z: pale olive green or yellow; strongly pleochroic, absorption Y > X > Z
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| | Zoning | - |
|
|
| Form | Habit | Elongate-bladed |
| | | Surface | Anhedral |
| | Cleavage | Poor; {001} parting |
| | Twinning | |
| | Extinction | |
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|
| Reaction textures | |
| | Alteration / decomposition | |
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|
| Occurence | Ign | |
| | | Met | Kyanite-talc-quartz schist |
| | | Sed | |
| | | Hyd | |
| | | Other | |
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|
| Distinctive properties | High relief, colour and pleochroism; restricted occurrence |
| | Additional comments | |
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