In this work, the reactivity of the surface of bituminous schists has been studied using a cation adsorbent, so-called Methylene Blue (MB). This bituminous schist is a calcareous clay rock that contains some amounts of organic matter. The samples were collected from an outcrop of Lamsied (Laâyoune), zone around Tarfaya-Boujdour. Once the granulometry of samples was well determined, the rocks were characterized by X-ray diffraction and they were analysed by X-ray fluorescence. Some parameters were considered relevant on the adsorption of MB by surface rock and they have been studied. One of these parameters is the adsorbed molecules-adsorbent contact time. This is the contact between a starting concentration of MB and a certain mass of gross rock. The analysis of results has shown that adsorption of MB can be well modelled by the Langmuir isotherm and also that a rapid kinetic (<100 min for L-type) can be fitted by a second-order equation model. The gross rock takes 84 % of the amount of MB in aqueous phase at a time less than 1min, using a rock mass of 0.1 g.