- Color: red, purple red
- Hardness: 9
- Refractive index: 1.76 - 1.78
- Density: 3.99 - 4.06
- Chemical composition: Al2O3
- Crystal structure: hexagonal
- Origins: Burma, Sri Lanka, Thailand, Cambodia, Vietnam, Madagascar, Tanzania, Kenya.
Rubies, the red variant of corundum, are the most expensive gemstone after diamonds. The distinctive 'pigeons blood' colored rubies from Mogok (Burma, or Myanmar as it is now referred to) have the highest value. Specimens over 5 ct. as well as eye clean stones are very rare. Heat treatment is usually applied to improve their color and reduce small inclusions.