Although nearly all of the crystal skulls have at times been identified as Aztec, Toltec, Mixtec, or occasionally Maya, they do not reflect the artistic or stylistic characteristics of any of these cultures. The Aztec and Toltec versions of death heads were nearly always carved in basalt, occasionally were covered with stucco, and were probably all painted. They were usually either attached to walls or altars, or depicted in bas reliefs of deities as ornaments worn on belts. They are comparatively crudely carved, but are more naturalistic than the crystal skulls, particularly in the depiction of the teeth. The Mixtec occasionally fabricated skulls in gold, but these representations are more precisely described as skull-like faces with intact eyes, noses, and ears. The Maya also carved skulls, but in relief on limestone. Often these skulls, depicted in profile, represent days of their calendars.