Hugoniot equation-of-state data of shock compressed aluminum oxynitride (AlON), consisting of 64.1 mol Al_(2)O_(3)·35.9 mol AlN with a density of ～3.68 g/cm~(3), have been determined to 180 GPa. The relationship between shock velocity (U_(s)) and particle velocity (U_(p)) is expressed by a straight line: U_(s)(km/s)=8.08+0.761U_(p)(km/s). Although there is no evidence of phase transition in the data, the determined Hugoniot of AlON has been compared with those of oxide spinels such as MgAl_(2)O_(4) and Fe_(3)O_(4). We discuss the systematics of high pressure phase transitions of spinels that indicate a phase transition to CaTi_(2)O_(4)-type phases. The phase transition to CaTi_(2)O_(4)-type structures implies that the recently discovered Si_(3)N_(4) spinel also may be transformed into a CaTi_(2)O_(4)-type phase with increasing pressure.
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