There is a very good blog called Arcane Radio Trivia which publishes interesting tidbits of radio trivia, and a lot of stuff that a reader might not have heard before, hence the name. A post put up last week, when I was out of town, deals with carborundum (Silicon carbide) which is one of the first semiconductors used to produce diodes, and thus detectors for radio.
Certain naturally-occurring minerals can be used to detect radio signals, including galena, zincite, silicon,bornite and others. Carborundum was unique among the early crystals because it was synthetic. It was durable, and at 9 mohs much harder than most available crystals. More here. Also interestingly it requires it requires a negative potential of 1 volt to be used as a diode. Carborundum was not created with this purpose in mind. It was created in the early search for artificial diamonds
Like many things in early radio, there are several plot twists in this story and if one is interested in radio history, it is work a click to read. While you are there, check out “It’s 105 degrees and rising“