- Types:
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alumina, aluminium oxide, aluminum oxide
any of various forms of aluminum oxide occurring naturally as corundum
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ruby
a transparent deep red variety of corundum; used as a gemstone and in lasers
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sapphire
a precious transparent stone of rich blue corundum valued as a gemstone
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alundum
a substance made of fused alumina
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star sapphire
a sapphire that when cut shows a starlike figure in reflected light because of its crystalline structure
