I was so totally fascinated with Nyle Steiner's article "Iron Pyrite Negative Resistance Oscillator" on the internet,  that I decided to make a curve tracer to investigate this phenomenon.

The article titled "PC Printer Port Controls I-V Curve Tracer" at the Dallas/Maxim Semiconductor site, shows a circuit for a curve tracer.  This device connects to the printer port of a PC and while under control of a Quick Basic program, sweeps positive and negative current through the test subject.  In this case, a small lump of pyrite.  On the computer screen a graph shows the current/voltage characteristics. Below is a photo of my setup.

The curve on the monitor shows that conduction is different in one polarity than the other, showing it behaves like a diode.  Pyrite is a  natural semiconductor !

So far I have not confirmed negative resistance, but I am not done with my investigations and believe it is possible.

I builted the circuit on a DT202 blank SimmStick and placed it in a DT002 Parallel Port expansion unit for interfacing  to a PC's printer port. SimmSticks are high quality, but inexpensive boards that can be purchased from Dontronics, an excellent company in Australia

Some modifications to the software were made to allow each sweep to accumulate on the screen, allowing changes over time to be observed.
 

Close-ups of Simmstick with DT202 board and device to make contact to the pyrite crystals. Nyle Steiner shows you how to make such a contact arm at his website.

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