A method is disclosed comprising placing in a hot pressing environment a controlled mixture of a first powder of Si.sub.3 N.sub.4 containing a controlled amount of SiO.sub.2 (with or without a limited amount of milling media) with a second powder consisting essentially of Y.sub.2 O.sub.3, hot pressing the controlled mixture, and cooling the resultant unitary object.A novel silicon nitride comprising a unitary object is disclosed which can be shaped to form a novel cutting tool useful for machining metal such as cast iron. The object has selected crystalline phases formed beta Si.sub.3 N.sub.4 and beta prime Si.sub.3 N.sub.4 and has intergranular crystalline secondary phases consisting essentially of YSiO.sub.2 N, Y.sub.10 Si.sub.17 N.sub.4 O.sub.23 and Y.sub.2 Si.sub.2 O.sub.7 with the YSiO.sub.2 N phase representing at least a 25% volume fraction of the secondary phases and comprising essentially all of the yittria-silicon oxide.