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| Formula | (Ca0.5,Na,K)6Al6Si12O36 ∙ 17H2O |
| | Optic class & sign | Uniaxial negative |
| | Relief | Moderate- to low-negative |
| | Refractive indices | no = 1.487 -1.502
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ne = 1.489 -1.510
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| | Birefringence (max.) | 0 002 - 0.008 |
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| | Sign of elongation | Length-slow, l (+) in elongate sections at a high angle to c |
| | Interference figure | |
| | Colour / pleochroism | Colourless |
| | Zoning | - |
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| Form | Habit | Thin tabular; sheaf-like aggregates |
| | | Surface | |
| | Cleavage | Normally not seen in thin section |
| | Twinning | Penetration twins on {0001} generally present |
| | Extinction | Straight to traces of {0001} faces in sections ∥ c (max Δn) |
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| Reaction textures | |
| | Alteration / decomposition | |
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| Occurence | Ign | |
| | | Met | |
| | | Sed | |
| | | Hyd | Cavities in basalt |
| | | Other | |
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| Distinctive properties | Hexagonal tabular habit, very low n, very low Δn, lack of cleavage |
| | Additional comments | Can be biaxial.
n-Δn charts A, B: Bre - brewsterite, Cpt - clinoptilolite, Epi - epistilbite, Hul - heulandite,
Lev - levyne, Stb - stilbite, Yug - yugawaralite |
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