The caustic fusion circuit is used to process samples weighing up to 500 kg to recover diamonds greater than 0.10 mm in size. The process sequentially utilizes attrition milling, heavy liquid separation and complete digestion of the rock by subjecting it to a strongly basic solution at high temperature (caustic soda). During the final step, virtually all of the minerals that constitute the kimberlite are rendered soluble except for the diamonds. The resulting residues are then observed microscopically to identify and recover the diamonds. The diamonds are measured in millimetres by sieving through square mesh screens. Because of the small size of sample, diamonds recovered by caustic fusion typically range in size from 0.10 mm to 1.70 mm.