I'm not sure which specific chemical it is. They were always swapping them around in different blends as new drug tests came out and restrictions changed. JWH-018 was pretty popular, JWH-073, AM-2201, HU-210 were all used. They are cannibinoids, some refer to spice as 'noids'.
I was addicted to the stuff while I was on paper for a while then got popped for it on a surprise test. Strange addiction for sure. I didn't even like it that much. Sometimes it felt a little like weed, sometimes like tripping harder than I have ever tripped. The difference is most of them are full agonists as opposed to partial agonists like weed. The stuff is bad news though. I've met people that had some pretty major health problems that resulted from smoking the stuff. Weird drugs, I won't ever touch them again and have no desire to. I took a bong rip one time off of what I believe to be was AM-2201 (called scooby snacks), I had a the only seizure I have ever had and was in the spirit world for a while. It was pretty crazy but totally sketchy. I think I was addicted to getting scared or something. They're bad news, stick to the green.