WB8AXI writes "Hello Radio Amateurs: My twelve year-old twin grandsons Jason and Jonathan have asked me to help them itemize the materials found in nature or simple 'contrived' items which might be used as radio detectors or as they put it, "could be used to detect radio-waves picked up through the crystal set they are supposed to build as a school project"? I put on my thinking-cap and noted; 'fools-gold' or galena: They said they ruled out diode transistors as they are man-made: Who will help GranPa with this question so he doesn't look foolish in the presence of his grandsons? Please assist me in listing the materials found in nature or any other simple home-made devices which will detect radio energy? F.M.[HANK]FABER, email@example.com "