This mineral is used as a refractory material in the steel industry:

The correct answer is a) magnesite. Magnesite is a magnesium carbonate mineral that is used as a refractory material in the steel industry. It is used to line furnaces and other high-temperature equipment to protect them from the heat and corrosion. Magnesite is also used in the manufacture of ceramics, glass, and other products.

Limestone is a calcium carbonate mineral that is used in a variety of applications, including construction, agriculture, and the manufacture of cement. Feldspar is a group of minerals that are used in the manufacture of glass, ceramics, and other products.