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| Formula | Mg(OH)2 |
| | Optic class & sign | Uniaxial positive |
| | Relief | Low- to moderate-positive |
| | Refractive indices | no = 1.559 -1.590
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ne = 1.580 -1.600
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| n increases with increasing Fe and Mn |
| | Birefringence (max.) | 0.010 - 0.021 |
| | | Strong dispersion; anomalous interference colours |
| | Sign of elongation | Length-fast, l (-) if flaky; fibres also length-fast, l (-) |
| | Interference figure | Commonly too fine-grained to obtain an interference figure |
| | Colour / pleochroism | Colourless |
| | Zoning | |
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| Form | Habit | Aggregates of flaky brucite (or less commonly fibres); may be contorted |
| | | Surface | Subhedral |
| | Cleavage | {0001} |
| | Twinning | None |
| | Extinction | Straight to {0001} |
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| Reaction textures | Hydrous retrogression of periclase in marble |
| | Alteration / decomposition | Hydromagnesite and other Mg-minerals |
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| Occurence | Ign | |
| | | Met | Magnesian marble |
| | | Sed | |
| | | Hyd | Veinlets in serpentinite or chlorite schists |
| | | Other | |
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| Distinctive properties | Low Δn, sign of elongation, occurrence |
| | Additional comments | |
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