Löllingite
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- Lustre:Metallic
- Transparency:Opaque
- Colour:Steel gray to silver white
- Streak:Greyish black
- Hardness:5 - 5½ on Mohs scale
- Tenacity:Brittle
- Cleavage:Distinct/Good Distinct on {010}{101}
- Fracture:Sub-Conchoidal
Löllingite is a quite rare form of arsenic oxide, heavier and more silver coloured than arsenopyrite which is otherwise quite similar. I found this specimen on Penlee beach, Newlyn - where it is fairly abundant among the pebbles and rocks on the beach, which are probably either waste from the nearby quarry, or mine, or naturally occurring from a lode just below the low tide range (a typically confusing Cornish situation).
Interestingly this mineral shows the limitations of curve tracing, it's a very reluctant semiconductor and quite hard to find good point contacts, as the mild curve shows. However I've had some good results with it in synth circuits - where it seems slightly better than arsenopyrite. This may be because in a live circuit it's exposed to many more fluctuations and different frequencies of signal than in a curve tracing setup - but more testing is definitely required.