MoS₂), and cerussite (lead carbonate, PbCO₃) Not all specimens of a crystal will function in a detector. Often several crystal pieces had to be tried to find an active one. Galena with good detecting properties is rare and has no reliable visual characteristics distinguishing it.

A rough pebble of detecting mineral about the size of a pea was mounted in a metal cup, which formed one side of the circuit. The electrical contact between the