Cholesterol stones are not hard, they are like sponge. I have done 4 Flushes so far and on each occassion i have removed many green Cholesterol stones. These stones block up the bile ducts (of which there are about 50,000) in your Liver and stop bile from coming out. Glad to learn you are doing well - keep it up. Keep flushing till about 2000 stones come out. I am surprised your stones are black, most people report green stones. Check out Dr Clarks web site to learn more.