Book 27, Question 82
Why is a ruby red and a sapphire blue if both are the same mineral?
Rubies and sapphires are both made of corundum, a very hard mineral made of aluminum and oxygen.
Pure corundum is clear. A tiny bit of chromium turns it red and makes a ruby, while traces of iron and titanium make it blue. Sapphires can also be yellow, pink, or green. Small amounts of other elements can make a big difference in color.
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Quick answers
Why is a ruby red and a sapphire blue if both are the same mineral?
Rubies look red because they contain trace chromium that absorbs blue and green light, leaving red light.
Source: sciencehistory.org
More fun facts
- Blue sapphires are also made of alumina, colored by iron and titanium.
Sources: sciencehistory.org