Abstract: A super hard-highly pure silicon nitride includes a preferentially oriented crystalline silicon nitride having a grain size of 1-50 .mu.m and a micro Vickers hardness of 3,000 kg/mm.sup.2 under a load of 100 g, a finely grained crystalline silicon nitride having an average grain size of less than 1 .mu.m and a micro Vickers hardness of 3,500 kg/mm.sup.2 under a load of 100 g, and an amorphous silicon nitride having a micro Vickers hardness of 2,200 kg/mm.sup.2 under a load of 100 g, and is produced by blowing a nitrogen depositing source and a silicon depositing source on a substrate heated at 500.degree.-1,900.degree. C. with a blowpipe composed of a pipe assembly wherein a first pipe for the nitrogen depositing source is surrounded with a second pipe for the silicon depositing source and the distance from an opening end of the first pipe to the substrate is shorter than the distance from an opening end of the second pipe to the substrate.