2020-12-23:
TV rock

This is a colorless mineral called ulexite, which has the unusual property of crystallizing in long, parallel fibers.

This gives it special optical properties: if you place it on top of a flat surface, the fibers will transmit whatever is on that surface to the top side, and display the image there – which is why ulexite is also known as TV rock.

It is mainly found in the eastern US, Chile, and Kazakhstan.