|Optic nature||Biaxial +|
|Refractive index||1.65 - 1.69|
Peridot is a Type II stone in the GIA clarity grading system is usually included. Typical inclusions are:
- disc like liquid and gas inclusions: "lily pads"
- dark, octahedral chromite crystals
The disc-like liquid and gas inclusions, often referred to as lily pads, appear doubled because of the strong birefringence that is a diagnostic characteristic of the gem.