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Precious stones
Semi-precious stones
Technical information
History of the stones
Characteristics :
Crystal structure : Rhombohedral Composition : Aluminum oxide
Specific gravity : 4.00 Hardness : 9
Refractive index : 1.76-1.77 Birefringence : 0.008
Variety : Corundum Pleochroïsm : pronounced (red orange, carmine)
Cut : Round  Emerald  Cabochon  Marquise  Ceylan  Oval

The colouring of the rubies is due to the chromium with sometimes iron.
The color is often distributed in an unequal way. Moreover, the ruby is a stone having often inclusions (liquid, crystals,…). Rutile inclusions allow the rubies cut out of cabochon to have the effects of asterism (star ruby or cats eye). The most seeked color is known as “blood of pigeon” (pure red with a hint of blue).

History :
Ruby takes from Latin “rubeus” meaning “red”. Before the XIXth century, ruby, red spinel and garnet were often confused and called “escarboucles”.
The most famous rubies are :
  • Ruby “Edward” in British Museum of London (167 cts)
  • Star ruby “Reeves” in Smithsonian Institute of New York (138 cts)
  • Star ruby “Length” in American Museum of New York (100 cts)
  • “Ruby of peace” (43 cts)

It should be noted that many stones present in the royal jewels were taken for rubies then after advanced analyses, proved to be red spinels :

  • “Ruby of Black Prince” (Crown of England)
  • “Ruby of Tamerlan” (Collar/royal jewel of England)
  • Pear ruby (Crown of Wittelsbach/Bavaria)
  • “Coast of Brittany” (Museum of Louvre)

Deposits :
The countries having deposits are :
Burma Important Some stones of higher quality  
Thailand Important Good rare quality  
Tanzania Medium Good rare quality  
Sri Lanka Medium Good rare quality  
Ural Weak Good rare quality