Amber
Fragment of a discussion from Talk:UALR Paleobiology ERSC 3360
An interesting detailed scenario about how this process occurs is located on this website,http://www.fossils-facts-and-finds.com/how_are_fossils_formed.html, under the heading "How are fossils formed?Amber".
This is an interesting site, with lots of information. however, be warned that it is a commercial fossil dealer's site and not a professional site, so the information presented on it has not been vetted as much as an academic site and may not be as reliable.