16.53: Peridot
- Page ID
- 5088
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| 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 |
Figure \(\PageIndex{1}\): Flawless faceted Peridot
Photo courtesy of Lembeck Gems
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
Figure \(\PageIndex{2}\): Lily Pad inclusions displaying doubling
35X Magnification
By Barbra Voltaire
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.