The fire clay contains pure

ANS:C - hydrated aluminium silicate

Fire clay is the main ingredient of refractory bricks that can withstand very high temperatures. It contains pure hydrated aluminium silicate. Fire clay is a range of refractory clays used in the manufacture of ceramics, especially fire brick. The United States Environmental Protection Agency defines fire clay very generally as a "mineral aggregate composed of hydrous silicates of aluminium with or without free silica".