The pressure dependence of the argentite-acanthite (Ag 2 S) and high-low naumannite (Ag 2 Se) transitions has been studied beyond 1,000 atm. The inversion temperatures, 176 degrees C. and 128 degrees C. are both raised less than 1O degrees C. by an increase of pressure of 1,000 atm. The usefulness of the presence of argentite and of high-naumannite as indicators of certain minimum temperatures is therefore enhanced, especially in analyzed samples.