Wolframite
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- Lustre:Metallic
- Transparency:Opaque
- Colour:Black; dark brown in transmitted light
- Streak:Brownish black to black
- Hardness:4 - 4½ on Mohs scale
- Tenacity:Brittle
- Cleavage:Perfect Perfect on {010}
- Parting:On {100} and {102}
- Fracture:Sub-Conchoidal
Wolframite is a bit of an old fashioned catch all term for a group of minerals, this one is probably Ferberite. These minerals are an ore of Tungsten, which was mined commercially in Cornwall during WW1 as tungsten is needed for high temperature uses. In Cornish mines it is commonly associated with cassiterite.
Officially listed as a semiconductor, I have had little to no success with it - probably due to it's relatively high resistance. I thought I had some interesting results with it when I first started experimenting with natural semiconductors but this may have been down to a specimen coated with something else, as recent tests have not worked at all. I tested the specimen in the photo, from Wheal Fortune, as well as some magnetically extracted detritus from crushed Poldice mine quartz which was rich in wolframite.