Corundum sapphire and ruby
Corundum is the hardest mineral other than diamond. Ruby and sapphire are the most valuable corundum. Red corundum is ruby, other colors are called sapphires, but there is no clear border between the two. Light red, pink or violet corundums are usually classified as sapphires whereas ruby is reserved for truly red stones. Read full article on: Corundum sapphire and ruby - More resources: Pandora bracelet jewelry
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