Hard Mineral: Red = Ruby and Blue = Sapphire
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Question is: Hard Mineral: Red = Ruby and Blue = Sapphire
and the answer is: CORUNDUM
Word Meaning:
CORUNDUM — (mineralogy) An extremely hard mineral, a form of aluminum oxide with the chemical formula Al₂O₃, that occurs in the form of the gemstones sapphire and ruby; it is used as an abrasive.
Definitions from Wiktionary.