ABSTRACT: THE PRESENT WORK IS CONCERNED WITH TRIBOLOGIC EFFECT OF AN ORGANIC LIQUID ON TRIBOLOGIC BEHAVIOUR OF MINERALS PARTICLES (GRAPHITE, HEXAGONAL BORON NITRIDE, NICKEL THIOPHOSPHATE, CALCITE). THE TRIBOLOGIC PROPERTIES ARE INVESTIGATED BY MEANS OF ALTERNATIVE SPHERE ON PLANE TRIBOMETER IN BOUNDARY LUBRICATION CONDITIONS. WHEREAS THE FRICTION COEFFICIENTS MEASURED UNDER AIR ARE HIGH (GRAPHITE µ=0.09, HBN µ=0.45, NIPS3 µ=0.23, CACO3 µ=0.35), THE ADDITION OF A LIQUID IN THE CONTACT INDUCES AN IMMEDIATE AND DRASTIC DECREASE OF THE FRICTION COEFFICIENT DOWN TO 0.05<µ<0.07. X-RAYS DIFFRACTION, FRETTING, NANOINDENTATION ANALYSES ALLOWED US TO ELIMINATE HYPOTHESES AS INTERCALATION OF THE ORGANIC COMPOUNDS IN THE LAMELLAR MATERIALS. TRIBOLOGIC EXPERIMENTS USING VARIOUS ORGANIC COMPOUNDS SHOW THAT THE IMPROVEMENT OF FRICTION PROPERTIES IS MAINLY DUE TO THE SIMULTANEOUS PRESENCE OF THE ORGANIC LIQUID AND THE SOLID PARTICLES IN THE SLIDING INTERFACE. TO EXPLAIN THIS EFFECT, TWO HYPOTHESES OFTHE STRUCTURE OF THE INTERFACIAL FILM OBTAINED ARE PROPOSED: NANOPOROUS OR NANOROUGH TRIBOFILM. TRANSMISSION ELECTRON MICROSCOPY  INVESTIGATIONS OF THE TRIBOLOGIC FILMS OBTAINED UNDER AIR AND IN PRESENCE OF A LIQUID DO NOT REVEAL SIGNIFICANT DIFFERENCES IN COMPOSITION.  RAMAN EXPERIMENTS SHOW  A REDUCTION OF THE MECHANICAL STRESS UNDERGONE BY PARTICLES IN PRESENCE OF THE LIQUID. THE INTERFACIAL PHASE STRUCTURE IS NOT COMPLETELY ELUCIDATED.