File:Fossil wood (Yld'aa, banks of the Indigirka River, Yakutia, Siberia, Russia) 2 (39189578895).jpg

Fossil wood from Siberia, Russia. (public display, Yakutsk Public Unified Museum of History & Northern Folk Culture, Yakutsk, Siberia, Russia)

The accompanying museum label refers to this fossil wood specimen as a "petrified tree", which implies that it has been three-dimensionally quartz-permineralized. The fossil is very likely from the upper Tertiary or Quaternary.

"Petrified wood" is a horrible term for what is technically called permineralized wood. Biogenic materials such as wood or bone have a fair amount of small-scale porosity. After burial, the porosity of wood or bone can get partially or completely filled up with minerals as groundwater or diagenetic fluids percolate through. The end result is a harder, denser material that retains the original three-dimensionality (or close to it). The wood or bone has become “petrified”. Well, no - it’s become permineralized. The most common permineralization mineral is quartz (SiO2). Sometimes, fossil wood or bone has been permineralized with radioactive minerals such as black uraninite (UO2) or yellowish carnotite (K2(UO2)2(VO4)2·3H2O). Recently, fossil bones permineralized with cinnabar have been identified - cinnabar is HgS - mercury sulfide.