Permineralization
Fragment of a discussion from Talk:Taphonomy
A good website with a lot of different pictures of petrified wood is http://petrifiedwoodmuseum.org/Permineralization.htm
http://oi53.tinypic.com/a3msld.jpg
Here's a picture of a fossil that has been permineralized, recrystallized, and replaced in places. You can tell it's perminerallized because you can see the internal molds formed by the minerals, most likely carried there by water travel.
