Slate
From London's Ghost Acres
Slate is a rock which can be made into roofing tiles, or used in electronic components as it is a good electric insulator as well as relatively chemically inert.
https://en.wikipedia.org/wiki/Slate
Slate is a rock which can be made into roofing tiles, or used in electronic components as it is a good electric insulator as well as relatively chemically inert.
https://en.wikipedia.org/wiki/Slate