Petrified wood and stone

Petrified wood is the name given to a special type of fossilized remains of terrestrial vegetation.
It is the result of a tree having turned completely into stone by the process of permineralization.

All the organic materials have been replaced with minerals (mostly a silicate, such as quartz),
while retaining the original structure of the wood.
Unlike other types of fossils which are typically impressions or compressions,
petrified wood is a three-dimensional representation of the original organic material.
The petrifaction process occurs underground, when wood becomes buried under sediment and is initially preserved due to a lack of oxygen which inhibits aerobic decomposition.
Mineral-laden water flowing through the sediment deposits minerals in the plant's cells; as the plant's lignin and cellulose decay, a stone mould forms in its place.