Reviewed by Hasitha K. Balasooriya · Managing Director, Gemszen (Pvt) Ltd · 8 years of gem-industry experience · Updated 6 October 2026
Corundum කියන්නේ aluminium oxide mineral එකකි. රතු gem-quality corundum Ruby ලෙසත්, අනෙකුත් වර්ණ Sapphire ලෙසත් හඳුන්වයි. Corundum වල Mohs hardness 9 වන අතර crystal system එක trigonal වේ.
Ruby and sapphire colours
Chromium is the principal cause of ruby red. Blue sapphire colour commonly involves iron and titanium. Corundum also occurs in yellow, pink, purple, green, orange, colourless and parti-coloured varieties, with colour influenced by trace elements and colour centres.
Important gemological properties
Corundum has Mohs hardness 9, no true cleavage and a trigonal crystal system. Typical refractive-index values are approximately 1.762–1.770 and specific gravity is close to 4.00. These properties support identification but do not replace full testing.
Natural, synthetic and treated corundum
Ruby and sapphire can be laboratory-grown by several methods, and natural stones are often heat-treated. Other treatments can include diffusion and fracture filling. Identity and treatment disclosure are essential in professional trade.
Frequently asked questions
Are ruby and sapphire the same mineral?
Yes. Both are gem varieties of corundum; colour and trade convention determine the variety name.
What crystal system is corundum?
Corundum crystallises in the trigonal crystal system.
Is every red corundum called ruby?
Gemological and trade boundaries between ruby and pink sapphire can vary, so colour interpretation may require expert judgment.