Rock · Fossil / lapidary

Petrified wood

SiO2 (chalcedony/opal replacing wood)

Petrified wood is wood replaced by silica (chalcedony, opal or quartz) while retaining cell structure, from Arizona's Chinle Formation (Araucarioxylon, Triassic), Oregon, Madagascar (Araucaria, Triassic), Indonesia and the Eden Valley of Wyoming. It is both a fossil and a lapidary material: polished slabs, bookends and full rounds are sold by weight. Petrified Forest National Park prohibits collecting, but private Arizona ranches sell legal material and Madagascar exports freely.

Formula	SiO2 (chalcedony/opal replacing wood)
IMA status	rock
Mohs hardness	6.5–7
Group	Fossil / lapidary
Type locality	None

Elsewhere

Cite this article

Stratum Study. "Petrified wood" (Mineral). Stratum Study pack 2026.09, as of 2026-09-19. https://stratum.black/study/minerals/petrified-wood. Accessed 2026-09-20.

BibTeX · CSL-JSON

@misc{stratum-petrified-wood,
  title        = {Petrified wood},
  author       = {{Stratum Study}},
  howpublished = {\url{https://stratum.black/study/minerals/petrified-wood}},
  year         = {2026},
  note         = {Mineral article, Stratum Study pack 2026.09, as of 2026-09-19; sources: stratum, wikidata, commons. Accessed 2026-09-20.}
}

Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.