Explanation: The composition of good brick earth: 1) Silica ● Good brick earth should contain 50 – 60% of silica. ● It prevents cracking, shrinking and wrapping of raw bricks. ● Silica imparts uniform shape to the bricks. ● Excess of silica makes the bricks brittle. 2) Alumina ● Good brick earth should contain 20 – 30% of Alumina. ● Alumina imparts plasticity to the earth so that it can be moulded. ● If it is excess raw bricks shrink and warp during drying and burning. 3) Lime ● It should not be greater than 5% for good bricks 4) Iron oxides ● It should be in the range of 5 – 6% for the good bricks. ● It imparts colour to the brick. 5) Magnesia ● It imparts color to the brick. ● It also decreases shrinkage in the bricks.