Abstract: In a method of forming a ceramic material of the kind including at least 90% by weight of a single phase silicon aluminium oxynitride which has a crystal structure based on .beta. silicon nitride but of increased unit cell dimensions and which obeys the general formula:Si.sub.6-z Al.sub.z N.sub.8-z O.sub.zwhere z is greater than 0 and less than or equal to 5, a ceramic intermediary is produced which contains a silicon aluminium oxynitride which obeys a different formula from said general formula. The intermediary is then heated in powder form at a temperature between 1200.degree. C and 2000.degree. C in a protective environment with at least one compound containing two or more of the elements silicon, aluminium, oxygen and nitrogen, the composition of said intermediary and the amount of said at least one compound being such that said intermediary is converted at said temperature into said ceramic material.