The black stuff in the rock appears to be a mineral deposit,...

The black stuff in the rock appears to be a mineral deposit, likely to be something like manganese oxide, graphite, or possibly a type of sulfide mineral such as pyrite or galena, depending on the geological context. To determine the exact nature of the black material, one would typically conduct mineralogical tests such as streak, hardness, and other diagnostic tests. If this is part of a field study or rock sampling, it would be advisable to send a sample to a geological lab for precise identification.

And that is what sum might let us know on monday regarding various rock chips and samples that were taken. IMOP.