Pyrite

• Lustre:Metallic
• Transparency:Opaque
• Colour:Pale brass-yellow
• Streak:Greenish-black
• Hardness:6 - 6½ on Mohs scale
• Tenacity:Brittle
• Cleavage:Poor/Indistinct Indistinct on {001}.
• Fracture:Irregular/Uneven, Conchoidal

[pyrite page on mindat]

One of the most common semiconducting minerals, pyrite exhibits high conductivity and easily provides a voltage drop - often in both polarities equally, rectification is harder to find than some minerals.