Are there cases where blood comes as little hard black stuff in sperm? there is no visible discolouration of sperm is it a cause of concern?

Need clarification: Pl rephrase your question to indicate if you mean semen instead of sperm, which can not be seen with a naked eye. Also, did this happen once or repeatedly? To properly diagnose what some dark stuff coming behind the semen could be, may be a sample could be shown to your primary doctor. Good luck

Corpora amylacea: Some guys' prostate glands make little hard stony things and you can ejaculate them if they get free. There not a problem.