The bauxite deposit, a lens in Devonian strata of the Portilla de Luna valley area, consists mainly of gibbsite (54-58 percent) and hallysite. The footwall slates contain fossils indicative of a lower Eifelian age and a shallow-water depositional environment; the fossiliferous limestones overlying the deposit are Givetian, indicating that laterization took place in the upper Eifelian. Subsequent metamorphism has resulted in partial crystallization of the material.