Fossil shown is actually 8 inch long, and found as an erratic in boulder clay.
Identification is by Colour weight and the streak. Colour is just like coal black, thus is the reason that coal is sometime miss-identified as jet if not properly tested. Weight again is the same light feel as coal. Streak is the term given to the colour left when scratched on a white surface; in this case jet leaves a nice brown colour.
This sample clearly shows a bark tree effect (please note not all pieces of jet show signs of being formally a tree).