Corundum · July birthstone
Ruby
Red corundum, the most valuable coloured stone per carat.
- Hardness
- Mohs 9
- Toughness
- Excellent
- Daily wear
- Excellent for daily rings
- Price tier
- USD 2,000 to 50,000+ per carat, fine quality
- Colours
- Red, Purplish red, Pinkish red
- Origins
- Myanmar (Burma), Mozambique, Thailand, Madagascar
Ruby is corundum coloured red by chromium. The finest colour, a vivid, slightly bluish red called pigeon’s blood, comes historically from Mogok in Myanmar and today also from Mozambique. Fine unheated rubies above two carats are rarer than diamonds of the same size and priced accordingly.
How to buy ruby
Colour first: vivid saturation and medium tone. Buy stones above one carat only with a report from GIA, SSEF, Gübelin, GRS or AGL stating origin and treatment. Heated rubies are the sensible purchase; unheated ones carry large premiums.
Treatments
Heating is routine and accepted; glass filling and diffusion must be disclosed and lower the value sharply.
Care
Warm soapy water and a soft brush; ultrasonic is safe for untreated and heated stones, never for glass-filled ones.
Lore
Called the king of gems in Sanskrit texts; Burmese warriors believed rubies made them invincible in battle.
