Composition of bricks:- Alumina : - It is the chief constituents of every kind of clay. A good brick earth should contain about 20-30% of alumina. It imports plasticity of earth. Silica:- Brick contain about 50-60% of silica. It present cracking, shrinkage and working of raw bricks. Line : It should be present in finely powdered state and not in lump. It prevent shrinkage. Iron oxide:- About 5-6% us desirable in brick earth. It helps line to fuse sand. It impart red color to bricks. Magnesia : - It impart yellowish tint to bricks and decrease shrinkage.