You have water in the system somewhere as that picture looks 100% like a rusty plug, I have in my collection of hundreds of plugs ones that look like that, I will try to find them and take a picture.
Ironically this is what plugs should look like even in a water injected engine like I run (details included for reference)
For those not familiar with rotary engines: (leading plug holes have a large opening to the combustion chamber and trailing plug holes have a smaller shielded hole) I use this visual check + EGT reading to balance any differences in the fuel air balance.
FL = front leading spark plug
FT = front trailing spark plug
RL = rear leading spark plug
RT = rear trailing spark plug
NGK 10 heat range plugs are 2000km old, run a 0.020" gap, Optimax Shell 98 Ron fuel, Mobil 1 engine oil (oil injected into motor), and Sthil 2 stroke premix at 180:1 mixed in with fuel also
10.9:1 AFR with 1.20kg/cm boost and 500cc Water Methanol at 50/50 mix, engine operating temp is 77~79 deg C
In case anyone is bored! Look On !!!
Front Rotor
Rear Rotor
http://images.google.com.au/imgres?i...a%3DG%26um%3D1
^ This site a bloke does a running analysis of thousands of miles of various plugs in his mazda, though of little relevance to this its a nice read anyway, with lots of relevant pics.