Mica "During the excavations at Teotihuacan, of one of the complexes was found to contain a basin lined with mica. It isn't understood why this 10 x 4-foot (3x1.2m) trough exists. There is an overhand sheltering the that is about 6 inches (15cm) deep. I don't know if this feature was watertight. Maybe it actually held water."
A foundation offering at the Teotihuacan pyramid discovered by tunneling excavators.