Chemically vapor deposited (CVD) Si3N4 is one of the highest purity forms of Si3N4 currently available, so the protective silica scale formed during oxidation in a pure oxygen atmosphere is also of high purity. The oxidation of CVD Si3N4 and CVD Si(3)M(4) coated graphite in 1 atm dry oxygen at 1500 degrees C has been measured and is compared with results from the literature for the growth of high purity silica on CVD Si3N4 and on CVD SiC.