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3DRuby. (External Sample)
Ruby, the name given to the red form of corundum, is just simply aluminum oxide. It's very hard: Common sandpaper is made with aluminum oxide grit. Artificial rubies are dirt cheap because they are easy to make. Natural rubies are very expensive because they are hard to find.
This specimen is natural, but not clear "gem quality" ruby, which of course makes it much less expensive.
Location: John Gray's Collection
Photographed: 11 March, 2003
Size: 3"
Composition: Al2O3