What is chalk considered?

Explanation:

Chalk, soft, fine-grained, easily pulverized, white-to-grayish variety of limestone. Chalk is composed of the shells of such minute marine organisms as foraminifera, coccoliths, and rhabdoliths. The purest varieties contain up to 99 percent calcium carbonate in the form of the mineral calcite.

Chalk is a salt because it has a calcium base; you can tell that it is a salt because it is powdery. It's formula is CaCO₃, or calcium carbonate.