Marcasite
More actions
- Lustre:Metallic, Sub-Metallic
- Transparency:Opaque
- Colour:Pale brass-yellow, tin-white on fresh exposures.
- Streak:Dark-gray to black.
- Hardness:6 - 6½ on Mohs scale
- Tenacity:Brittle
- Cleavage:Distinct/Good Distinct on {101}. {110} in traces.
- Fracture:Conchoidal, Sub-Conchoidal
Marcasite is chemically identical to pyrite but has a different crystal structure and is more silver in colour. It seems quite rare in Cornwall, it's taken me a long time to find any. This could be due to the fact that it's massive form is very similar to arsenopyrite, and I may have overlooked it in the past. This specimen is really nice though, very reflective and large well formed crystals. Marcasite is a mineral that forms 'hopper' crystals, stepped hollow forms similar to salt crystals.
I had a surprise getting a curve trace from it, I was expecting it to behave like pyrite - which is easy enough to find spots with a voltage drop and quite leaky, but functioning asymmetric rectification properties. However it seemed like a very good conductor all over, and only with a lot of patience could I find the curve I captured, with a very slight notch at around -0.5V. This actually seemed like it was present in different spots, so I'm fairly confident it is a property of the crystal. I tried it with silver (which was far too conductive) and steel as a cat's whisker.