Multiple choice

Ruby and sapphire are oxides of

  1. copper

  2. tin

  3. iron

  4. aluminium
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Ruby (red due to chromium impurities) and sapphire (blue due to iron/titanium impurities) are both gem varieties of the mineral corundum, which is crystalline aluminum oxide (Al2O3). They are among the hardest gemstones after diamond.

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