Jet is just like Succinic an organic material having a low density.
Originated from ancient forest
As amber is git by static friction. Git is under high pressure into layers of mud caused by the compression of 135 million year old wood. Git is excellent machinability and for centuries popular for jewelry making.
Jet-black beads at the megalithic tombs
Even when the megaliths in Drenthe are all beads of this black material found. Due to its deep black color also speaks of 'jet black'. Git is seen as absorber of negativity.