I performed a few experiments in this regard some while back it does work
and yes I tend to agree with you about the Basalt and Granite of the old
monuments. Its also interesting to note that Brown thought an improvement of
his Petrovoltaic batteries could be built with what appears to be some sort
of electret involving Tungsten Carbide and Wax cooled in a high tension
field, I still want to attempt this but the tungsten carbide powder is
proving to be a problem to obtain.
Regards
Martin
http://www.geocities.com/CapeCanaveral/Lab/7919/