Bones do not have to be “turned into stone” to be fossils, and usually most of the original bone is still present in a dinosaur fossil… Fossilization is a process that can take anything from a few hours to millions of years…The amount of time that it takes for a bone to become completely permineralized is highly variable. If the groundwater is heavily laden with minerals in solution, the process can happen rapidly. Modern bones that fall into mineral springs can become permineralized within a matter of weeks.
Curie, Philip J. and Koppelhus, Eva B Questions about Dinosaurs, Dover Publications, 1996, Pg.11.
Note: Dr Philip Curie is the founder and curator of the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta, Canada, and is Professor and Canada Research Chair in Dinosaur Paleobiology at the University of Alberta.