I can rush, I can be still, I can be hot, I can be cold, I can be hard, I can slip through almost anything. What am I?

Question

I am rich but I cannot be poor, I can be dark and I can be white, I can be hot or I can be cold, I can be a powder or I can be in pieces, I can be French or Belgian, I can be raw and can be especially sweet and even addictive. But one thing is for sure having too much of me can make your body a little jittery. What am I?