| Crystal System |
Orthorhomic |
| Chemical Comp.. |
Al2SiO5 |
| Color |
Usually
colorless, can be pink or green |
| Pleochroism |
None
in colorless varieties; slight in colored varieties |
| Cleavage |
1
good, 1 poor @ 89˚ |
| Relief |
Moderately high |
| Birefringence |
First order gray-white |
| 2V | 73˚ to 86˚ |
| Optic Sign | Negative |
| Twinning |
Rare simple |
Shown in the photomicrographs are prismatic sections of andalusite. Cross-sections oten contain a diagonal cross of impurites, called a "Chiastolite Cross" (see below).
