silver slag/dross (see Molina); i.e. what is wasted in the silver mining process?
Alonso de Molina:
iztac teocuitla popozoquillotl. escoria de plata. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 49r. col. 2. Thanks to Joe Campbell for providing the transcription.