From The Gemology Project
Jump to: navigation, search
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
Flawless faceted Peridot
Photo courtesy of Lembeck Gems


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
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.