Solved UPSC CDS/OTA Question
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Q · Mineralsmedium · 45s
Which mineral is commonly used as a gemstone and has a hardness of 9?
TopicMinerals
Question Typemultiple choice
Difficultymedium
Marking+1 / −0.33
Test Duration30 min
Step-by-Step Solution
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Corundum, with a hardness of 9 on the Mohs scale, includes the precious gemstones ruby (red corundum) and sapphire (all other colors). Composed of aluminium oxide (Al₂O₃), corundum's exceptional hardness makes it valuable not only for jewelry but also for industrial abrasives and cutting tools. The color variations result from trace amounts of elements like chromium (ruby) and iron or titanium (sapphire).
Final Answer: Option B - Corundum