CrazySlasher, the graphite was mixed with animal fat, say bear fat, and then applied as black body pigment. Here's a piece from RI. You can see what results just rubbing it directly on my finger for a few seconds. Greasy! (Graphite is the "lead" in lead pencils).
I love pickin this stuff up, but I'm guessing many collectors will walk right by not realizing what it is. I really like the idea someone used the rock to paint their face or body long ago.