A good class brick consists of 20-30% of Alumina. Excess of Alumina in clay makes the brick crack and wrap on drying.
In general, bricks are made with 50-60% of Silica in it. Excess of Silica in brick makes the brick to brittle.
Brick consists of 0.8-2% of Lime in it. Excess of lime in brick may cause to melt and distort during burning.
Magnesia, Sodium, potassium, manganese and iron oxide.