Abstract: Proppants and methods for their preparation are described herein. The proppants can be prepared by a process comprising (a) directing the molten slag material at a temperature above 1300° C. to an atomizing apparatus to output the molten slag material in the form of atomized droplets, (b) projecting the droplets of the molten slag material, wherein a substantial portion of the droplets at least partially solidifies in flight, (c) maintaining the at least partially solidified droplets at a temperature between 700° C. and 1300° C. to provide proppant particles having a crystalline phase; and (d) cooling the proppant particles to below 700° C. Methods for hydraulic fracturing of a well in a subterranean formation having a fracturing stress are also described herein.