Razor blade diode

Rediscovering a trick from the old days - instead of using a cat's whisker, you can balance crystals on razor blades to create the point contacts.

It works, you need to rotate the crystal around to find a good contact, and it's a bit easier than fiddling with a cat's whisker in some ways. I managed to get some good results in testing but it does have a couple of drawbacks.

Firstly it's pretty dangerous! Secondly it relies on one side creating the point contact with the other creating the normal ohmic connection. There is nothing stopping it happening in reverse, or both (or neither) so it sort of creates the necessity of more fiddling.

Thirdly I realised a big factor is the weight of the specimen - it will need to be just right, unlike the cat's whisker which you can adjust and remains the same regardless of the sample you use.

Curve test results

The curve on the left is cassiterite which is the best I've seen with this mineral in terms of rectification. I'm wondering if the quite substantial mass of this sample had something to do with this (I'm not splitting this one up into smaller chunks, it's one of the best rocks I've found!). It had very low current flow, as seems usual with this specimen though.

On the right is arsenopyrite which is fairly typical, higher resistance with negative biased, but leaky.

Two chalcocites with very different curves, Penstruthal on the left and Wheal Prosper on the right. I've never seen such an S shaped curve as the Penstruthal one though, chalcocite is a fairly eager semiconductor, so I think must be the response of a point contact formed on each blade.