Peridot
From The Gemology Project
Peridot | |
---|---|
Chemical composition | (Mg,Fe)2SiO4 |
Crystal system | Orthorhombic |
Habit | Prismatic |
Cleavage | Poor |
Fracture | Conchoidal |
Hardness | 6.5 |
Optic nature | Biaxial + |
Refractive index | 1.65 - 1.69 |
Birefringence | 0.036 |
Dispersion | Medium, 0.020 |
Specific gravity | 3.34 |
Lustre | Vitreous |
Pleochroism | Weak |
Magnification
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.