Galena (lead sulfide) is one of the most sensitive minerals
use in crystal radios. Most of the galena I've encountered in
rock shops, etc. is the stuff with large crystal structure.
However, the galena used in the old days had a much finer crystal
structure. It was known as steel galena due to having the
appearance of a broken piece of cast iron or steel. It's
generally easier to find, and hold, a sensitive spot on this
material. There have been some suggestions that this may be
argentiferous (silver bearing) galena.
These are vintage detectors, from
manufacturers, mounted in lead
mounts are about 0.5" in diameter. I sure wish I could find
pound or two of this material. It would make a lot of
detectors. See Mounting