Ruby Overview

• Name: Ruby

• Family: Corundum

• Chemical Formula: Al2O3 (aluminum oxide)

• Color: Red (due to chromium)

• Hardness (Mohs): 9 (second only to diamond)

• Crystal System: Trigonal

• Luster: Vitreous (glass-like)

• Transparency: Transparent to translucent

Color – The Most Important Factor

Ruby’s value is defined by its color, which must be red — no other color qualifies it as a ruby, even if chemically identical.

• Best color: “Pigeon’s blood” red – a vivid, pure red with a slight bluish tone

• Other tones: pinkish-red, purplish-red, orangey-red, brownish-red

• The red comes from chromium; more chromium = deeper red

If a corundum is any color other than red, it is classified as a sapphire, not a ruby.

Origins and Sources

Top-quality rubies are found in:

• Myanmar (Burma): Home of the finest rubies, especially from Mogok

• Thailand: Darker rubies, often with brown or garnet-like tones

• Sri Lanka (Ceylon): Lighter “pink sapphires” and ruby varieties

• Madagascar: Newer source of bright, clear stones

• Mozambique: Major modern source with high-quality stones

Clarity & Cut

• Clarity: Most rubies have inclusions. Eye-clean stones are rare and valuable.
  

  • Common inclusions: rutile “silk,” fingerprints, needles, or crystals

• Cut: Often cushion, oval, or mixed cuts to maximize color and brilliance

• Carat: Large rubies (over 1 carat) are exponentially more valuable due to rarity

Treatments

Most rubies undergo treatments to improve appearance:

• Heat treatment: Common and accepted; enhances color/clarity

• Fracture-filling with lead glass: Makes heavily included stones look better but lowers value

• Untreated rubies: Very rare and command premium prices