In an adsorption study from a liquid mixture, the choice of a moderately hydrophilic silica and of a solute like 2,5-dimethylpyridine (2,5-DMP), known for its layering ability in dilute solution in water, allows the observation of several adsorption gaps on the isotherms established at different temperatures. These gaps may be attributed to surface phase transitions. Collected on a (T-Γ21) diagram, they constitute a surface phase diagram highly similar to the bulk water-2,5 DMP liquid-solid diagram at low temperature. It is the first example of a surface phase diagram at a liquid-mixture/solid interface.