Thanks to all for updating. Great to have an analysis.

Not so impressive, actually. A friend (Eric) has a similar specimen we happened to look at while working on all the U minerals from DRC I've been posting. He had it labeled as chalcocite, too. He's not great with crystal forms and when I noticed the forms were wrong, we started looking at the relevant mindat pages and found the photo up top matched it but was also apparently mislabeled. So I photographed and posted Eric's (inserted here). 

I guess I have seen so many chalcocites and bornites from the Bristol, Connecticut copper mine that I have gotten good at telling them apart, even when massive. We're only as good as the rocks and minerals we've seen, maybe? :-)