A method of making high purity crystalline AlON bodies by synthesizing and calcining AlON powders having less than 80 ppm Si, Mg, Ca, Na, and K impurities. The AlON powders are milled to reduce the particle size of the AlON powders using a high purity milling media. An AlON body is formed from the milled AlON powders. Such AlON bodies are particularly suitable for semiconductor process chamber components.