|
| Formula | AlO(OH) |
| | Optic class & sign | Biaxial positive |
| | Optical orientation | X = c, Y = b, Z = a |
| | Optical plane | (010) |
| | Relief | High |
| | Refractive indices | nx = 1.682 -1.706
|
|
ny = 1.705 -1.725
|
|
nz = 1.730 -1.752
|
|
| - |
| | Birefringence (max.) | 0.040 - 0.048 |
| | | - |
| | Optic Angle
| 2Vx
|
| | 2Vz
= 84 - 86° |
| | Sign of elongation | Length-slow, l (+), or length-fast, l (-), depending on whether cut is closer to Z or to X in platy crystals |
| | Interference figure | Commonly impractical due to fine grain size |
| | Colour / pleochroism | Colourless; may be pale reddish-brown or violet to pale greyish green or green; absorption Z > Y > X |
| | Zoning | |
|
|
| Form | Habit | Fine-grained aggregates of tiny scales or platelets, fibrous |
| | | Surface | |
| | Cleavage | {010} perfect |
| | Twinning | Usually not twinned |
| | Extinction | Straight to cleavage and main crystal faces in sections ∥ b |
|
|
| Reaction textures | |
| | Alteration / decomposition | Relatively stable; diaspore is itself an alteration product of aluminous minerals |
|
|
| Occurence | Ign | |
| | | Met | Al-rich metamorphic rocks (metabauxite and metamorphosed laterites, emery deposits), marble |
| | | Sed | Bauxite, laterite, aluminous clays |
| | | Hyd | Altered felsic igneous rocks |
| | | Other | |
|
|
| Distinctive properties | High n, moderately high Δn, mineral association. Optical identification may be difficult due to small grain size. |
| | Additional comments | Does not stably coexist with quartz, except at high pressures (> 12 kbar); coexists with coesite under ultrahigh-pressure conditions |
|
|
Images 
