Fat necrosis is a form of necrosis characterized by the action upon fat by digestive enzymes.
In fat necrosis the enzyme lipase releases fatty acids from triglycerides. The fatty acids then complex with calcium to form soaps. These soaps appear as white chalky deposits.
It is usually associated with trauma of the pancreas or acute pancreatitis.
It can also occur in the breast, the salivary glands  and neonates after a traumatic delivery.
Fat Necrosis of the breast