G is for Galena
Wikipedia states: 'One of the earliest uses of galena was as kohl, which in Ancient Egypt, was applied around the eyes to reduce the glare of the desert sun and to repel flies, which were a potential source of disease.
Galena is a semiconductor with a small bandgap of about 0.4 eV which found use in early wireless communication systems. For example, it was used as the crystal in crystal radio sets, in which it was used as a point-contact diode to detect the radio signals. The galena crystal was used with a safety pin or similar sharp wire, which was known as a "cat's whisker". '
More information is at Digital Geology. And I notice that two of my blogs make reference to galena. One a poem, Galena Whispers, and the other is a short prose piece, Old-Time Radio, with a link to a site where you can listen to radio from the past. I love that place.
Some years ago, a tour of a local mine produced samples of galena and this not-very-great photo is of one of those samples. It's not your regular rock.
♥ ♥ ♥