"The mineral corundum which includes the precious stones ruby, sapphire, and topaz, contains alumina, or aluminum oxide, Al2O3. It is found in nature crystallized in rhombohedral forms, having a specific gravity of 3.9, and is scarcely inferior in hardness to diamond." —Hallock 1905

Aluminum

"The mineral corundum which includes the precious stones ruby, sapphire, and topaz, contains alumina,…

Beryl is a mineral containing beryllium and aluminum in the form of a silicate.

Crystal of Beryl

Beryl is a mineral containing beryllium and aluminum in the form of a silicate.