Quote:
Originally Posted by Bob Steele
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Ruby and Sapphire are both transparent aluminum(Al2O3). Sapphire is sometimes used as viewing windows in ultra high pressure and high temperature lab equipment. The color of ruby and sapphire is just based on the impurities in the crystal lattice, no impurities and it's clear like glass.
btw: this means all the aluminum you own is literally covered in sapphire.