How to find semiconductors in Cornish mine waste

On the right is an image of a typical Cornish mine dump, this one is at Wheal Prosper, St Hilary. Its been cut through to provide access to a field, and you can clearly see how layers have been deposited - perhaps from different areas of the mine, or different depths, containing different minerals.

The art of collecting minerals from mine waste is known as "fossicking", scanning the surface workings and locating rocks that may contain crystals of interest. Most often in the case of searching for semiconductors, we are looking for metallic mineralisation - the most abundant metal is iron, which is often associated with rarer metals. We are looking for heavy, red or yellow iron stained rocks - often coated in goethite, which is one of the minerals that comprises rust.