What are the black fragments that appeared after hydrochloric acid was added to zinc in a test tube?

We did a lab in chemistry class today and one of the steps included adding hydrochloric acid to a piece of zinc in a test tube. There were some black fragments at the bottom of the test tube after the reaction occurred (we also held an ember to the mouth of the tube and it began smoking too). So what are those black pieces exactly...? Thanks ^_^.|||If your zinc and hydrochloric acid were reasonably pure there shouldn't be any black fragments left over when the reaction is complete.





However, since you mention the ember, it seems likely that some of the burnt ember fell into your test tube, in which case the black fragments are mostly carbon.