Summary: Grandidierite has been found in hornfelses around a diorite stock on Cuvier Island. Physical properties and electron microprobe analyses are given for two Cuvier Island and two Madagascan grandidierites. The Cuvier Island grandidierite has crystallized under conditions of the K-feldspar-cordierite hornfels facies at temperatures of approximately 600°C. and pressures (P_load) of less than 300 bars.