Carbon Fiber Hazard
Your right tree magnet it is called activated charcoal, but is almost completely made up of carbon. This is the same stuff used in water filters. I am a rower, and recently one of my rowing buddies broke an oar while racing. The oar he broke, the shaft was made from carbon fibre. The boatman was worried about people touching the shattered area because the carbon fibres can work their way into your skin and will not come out, i guess down at the microscopic level they have little barbs or something on them. While i don;t think the carbon itself can cause a problem it may be the resin used. Whether it is the safer epoxy or more harmful polyester may not matter. The chemicals in the resins could possibly be broken down into more harmful chemicals or maybe just cause damage by themselves. It's beyond me. I do know for sure though that normal carbon, be it fibre or not is safe to ingest, therefore should be safe to handle or get on your skin.