It's important to note that aluminum oxide is not a single mineral, but a compound composed of aluminum and oxygen. It's a very common mineral, and it exists in a variety of forms, including corundum and emery.
Corundum is a pure form of aluminum oxide, while emery is a mixture of corundum and other minerals like magnetite and hematite.
The aluminum oxide in an emery board is usually in a powdered form, and it's mixed with a binder to hold it together. The abrasive properties of aluminum oxide make it ideal for smoothing and shaping nails.