Assertion: α alumina | /r/HasProperty | the most stable form of al 2 o
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Source sentences:
text: Sapphire, ruby, and pure corundum are α-alumina, the most stable form of Al 2 O 3 , in which 3 electrons leave each aluminium ion to join the regular octahedral group of six nearby O2− ions; in pure corundum this leaves all of the aluminium ions with a very stable configuration of no unpaired electrons or unfilled energy levels, and the crystal is perfectly colorless.