A green and black clot is unusual. Sometimes it could be a plug of mucous, or it could have been a polyp (polyps are benign growths that sometimes grow on the cervix or in the uterus, and they could just fall off in their own) that came off on its own. It also might have been a piece of tissue or of a tampon that remained inside and got full of mucous secreted by the vagina and cervix. It also could have been a very early miscarriage, and it was the tissue remaining from the pregnancy that didn t take. As long as it doesn t repeat itself, and your periods return to normal, you probably have nothing to worry about. However, if you continue to have these unusual clots, you should get examined by your gynecologist to figure out what is going on.