View source for Porthtowan/Nangiles exotic semiconductor field trip

One of the tasks I've been funded to do is "Researching mine history and searching mine sites for semiconducting material", and for the first trip of this project I decided to head to the north coast to check out a few places:

* [https://www.mindat.org/loc-216211.html East Wheal Towan] 
* [https://www.mindat.org/loc-216208.html Charlotte United Mine]
* [https://www.mindat.org/loc-210320.html Great Wheal Charlotte]

These are all within a short walk of each other near the cliffs between Porthtowan and Chapel Porth beach.  

And on the way back:

* [https://www.mindat.org/loc-194326.html Nangiles Mine]

The reason for these choices are that there are many semiconducting minerals that are very commonly found on the mine waste dumps in Cornwall, but I've been wanting to expand the possibilities a little. There are two that I've tested in the past but haven't been able to find enough of to use much.

* [[cuprite]] a red transparent copper oxide - common is some copper mines but not others, I think this is to do with the temperature of the mineral formations. I've found well formed but tiny specimens before, but the Porthtowan area seems to have larger amounts of less well crystallised material - perfect for use as natural semiconductors.
* [[wolframite]] an ore of tungsten, which Nangiles mine was used for mining at one time. I've seen [[negative resistance]] in this mineral before, which has potential to build more interesting circuits.