Mineralogical, chemical, and geological aspects of four types of clay deposits in Las Aguilas Formation northwest of Barker in Buenos Aires Province, Argentina, indicate that these products of lateritic alteration of Precambrian granite are predominantly kaolinitic with minor amounts of halloysite, illite, and chlorite. Minor amounts of quartz, feldspars, and ferric oxides are also present. Of the four types, one is suitable for high quality refractories, another can be used for wall tiles and china, and a third, the most abundant, can be used for red ceramics; the fourth has no special use. The abundance of the clays is calculated to exceed eleven million metric tons.