After a recent colposcopy & cervical biopsy i had a huge tissue sac filled with black stuff come out without warning. what caused that?

Need evaluation: Did you save the "sac filled with black stuff"? It may be a blood clot. You did not say if it came out of your vagina or rectum. In any case, you need to be examined to determine if there is a lesion either in your vagina/cervix, or colon. Please consult your doctor.

Coagulant: If the biopsy was an excisional biopsy, it is likely your doctor placed a solution on the cervix to slow bleeding called monsels solution. When this mixes with blood it turns black and has a coffee ground appearance. This may have been combined with gel foam or other coagulant tissue that might account for your experience, but i agree you need to contact your physician to be sure.