Corundum var Sapphire

Corundum var Sapphire

Ilmenogorsky alkaline complex, Ilmen Mountains,

Chelyabinsk Oblast, Russia

Photo by Tomer Shapira

Corundum Pegmatites are cool. You need an excess of aluminum in absence of excess silica to form this, which can happen in evolved alkaline magmas (Syenite, Nepheline Syenite, and their pegmatites), such as this rock from the Ilmen alkaline complex, which is a body mainly composed of Syenite and Syenite Pegmatites. Similar Corundum bearing rocks can be found in Ontario (near Bancroft), Norway (Seiland), Kenya (Garba Tula), and Myanmar (Mogok).