Certain plants do not become fossils but actually turn to stone. Petrified wood is one such fossil, as the plant remains are chemically altered by mineralization, thus eventually turning to stone. In a process that takes thousands of years, when water containing dissolved minerals—such as calcium carbonate or silicate—infiltrates wood (or plants), the minerals either replace or enclose the organism so the structural details of the plant remain. Botanists find these types of fossils to be very important since they allow for the study of the internal details of extinct plants.