As always; it can be hard to tell from a photo. My guess is that it is likely a contact point where a Quartz deposit or vein was running. Is the whole back side black? Can you take a few more photos from different angles? Thanks!
I'm with Burntbear. It looks to be a fragment of quartz vein. The orange looks to be decomposed pyrite and the flashes look to be pyrite crystals. The black coating is also probably a mixture of iron materials and other minerals forming a crust on the vein. As BB said some better pictures and close ups will help a little.