Muscovite was ground in water, alkaline chloride solutions, methanol and toluene. The influence of the grinding medium was investigated using several methods, in particular by electron microscopy. It was found that the addition of lithium ions in aqueous media or NH3 to methanol facilitates the breakdown of the muscovite structure. The results are explained supposing that water or methanol form lubricating films on the mineral surface, the lubricating properties of both liquids being lost when a hydrogen-bond disrupting agent (Li+, NH3) is present in the grinding medium.