| Crystal System |
Orthorhombic (Pseudo-Hexagonal) |
| Chemical Comp.. |
(Fe2+,Mg)2(Si5Al4O18).nH2O |
| Color |
Colorless
to very pale blue |
| Pleochroism |
Weak:
pale yellow, green, violet-blue |
| Cleavage |
One
Poor, One Moderate |
| Relief |
Low |
| Birefringence |
Low 1st order |
| 2V | 35˚ to 106˚ |
| Optic Sign | Positive or Negative |
| Twinning |
Cyclic Twins common. |
| Special Features |
Usually contains lots of inclusions |
Occasionally, Cordierite (Cord) is stabilized in peraluminous granites, where it can breakdown to Muscovite (Mu).
