Areas of tissue undergoing necrosis aren't physiologically normal: they have altered conditions of pH, osmolarity, ionic composition, etc., as a result of their derangement. In certain circumstances this may lead to a condition of dystrophic calcification, the abnormal deposition of insoluble salts of calcium, especially calcium carbonate and calcium phosphate. Calcification is normal in some places (teeth, bones) but serves no function in most others. It's essentially a preciptation reaction. You will see it in instances of necrosis, especially in caseous necrosis; and in the necrosis of fat. Examples are shown below.
The deposited salts appear as gritty, basophilic material lodged in among the cells and/or cellular debris in discrete areas. They're inorganic material and have a semi-crystalline appearance to them quite unlike any cell. Combined with their intense basophilia (they bind the charged dye hematoxylin very strongly) they're not easily missed nor mistaken for anything else.