The orbital history of Triton, coupled to its thermal evolution, and the role played from obliquity tides [1, 2], together with the ongoing geological activity [3] suggest a differentiated interior, with an outer ice shell, a possible sub-surface ocean, and a deep-rocky interior. Triton’s deep interior could be hydrated, as suggested for other icy satellites, such as Titan [4, 5]. Antigorite (density: 2.5-2.6 g/cm3) is the most evocated mineral to explain the low estimated average density of the deep interior of icy moons [5]. Nevertheless, a model of a hydrated deep interior must consider the chemical environment, the lithostatic pressure, and the internal temperature, which define by their own the resulting mineral assemblages. Methods We adopt the algorithm Perple_X [6] to produce a pseudosection (Fig.1), modelling the stability fields of several mineral phases at thermodynamical equilibrium, in the function of pressure (P) and temperature (T). We select as the initial bulk composition of a proto-Triton a chondritic material. Results Figure 1 shows an Orgueil-like bulk composition simulating the rocky deep interior composition in a hydrated scenario. In addition to antigorite, we found that the mineralogy of hydrated deep interior should be characterized by the primary phases: amphibole, chlorite, antigorite, and talc, for the expected temperature and pressure of Triton’s deep interior and at a temperature lower than 980 K. For higher temperature we found that hydrated phases dehydrate in olivine and pyroxenes, as main phases. We plan to investigate the role of volatiles and ices in modelling the mineralogy of the deep interior. Acknowledgments G.M. and C.C., acknowledge support from the Italian Space Agency (2020-13-HH.0). References [1] McKinnon, W. B. (1984). Nature, 311(5984), 355-358. [2] Nimmo, F., & Spencer, J. R. (2015). Icarus, 246, 2-10. [3] Hansen C.J., & Kirk R. (2015), 46th LPSC, 2423. [4] Fortes, A. D., et al. (2007). Icarus, 188(1), 139-153. [5] Castillo-Rogez J.C., Lunine J.I. (2010). Geophys. Res. Lett.37(20). [6] Connolly, J. A. D. (2005). Earth Planet Sci Lett, 236.1-2:524-541.