| 1 | What size of ruby do you have? | |
| 2 | This corundum type of gem is formed from a variety of aluminum oxide . | |
| 3 | This corundum type of gem is formed from a variety of aluminum oxide . | |
| 4 | True rubies are, in fact, the red variety of a mineral called corundum. | |
| 5 | In addition, there are some special species, such as abrasives, such as sintered corundum. |
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