We have studied a lump of clay found at the archaeological site located in the hill of ’La Campana’ near the town of Yecla, Province of Murcia, Spain. The lump is part of an unused crushed coil. The X-ray diffraction analysis has shown the presence, mainly of illite, poorly crystalline smectite and, in a reduced proportion, of kaolinite. We can thus presume that exposure to a heat source was rather accidental. All minerals found in the lump of clay have a low degree of crystallinity and they coexist with amorphous material, especially iron oxide and even quartz and carbonates.