Petrified vs. agatized vs. opalized

Petrified wood is the umbrella term for wood turned to stone via mineralization. If the replacement/permineralization is primarily chalcedony/agate (quartz), you’ll see “agatized wood.” If the silica took the form of opal (hydrated silica), you’ll meet “opalized wood.” Many specimens mix phases.

What makes it special

Unlike charcoal or coal (altered, carbon‑rich remains), petrified wood preserves structure. Under magnification you can identify tree groups—conifers vs. hardwoods—by the anatomy baked into stone.

1) Rapid burial & shut‑off

Logs are buried by volcanic ash, river sediments, or landslides. Oxygen drops, decay slows, and the wood’s micro‑architecture is preserved long enough for minerals to move in.

2) Silica in solution

Groundwater, often circulating through volcanic ash or silica‑rich rocks, carries dissolved silica. This infiltrates cell spaces and begins depositing a gel of opal or micro‑quartz.

3) Permineralization

The gel fills lumina (cell cavities), preserving vessels, tracheids, and rays like a cast. Early stages are frequently opal‑A/AG (amorphous silica).

4) Replacement & maturation

Over time, silica can replace cell walls and mature from opal to chalcedony/agate (microcrystalline quartz). The log becomes a solid stone faithful to the original blueprint.

5) Coloration

Trace elements paint the palette: iron oxides (reds/yellows), manganese (blacks), organic carbon (browns), copper/chromium (greens, occasionally). Open cavities may finish with drusy quartz.

6) Erosion & reveal

Uplift and erosion bring fossil forests to the surface. Polishing reveals the rings and rays with gemstone clarity—geology’s love letter to dendrology.

Palette

• Nut‑to‑chocolate browns — carbon/iron mix, classic “wood” look.
• Reds & burgundies — hematite (Fe³⁺).
• Ochres/yellows — goethite/limonite (Fe³⁺ hydroxides).
• Charcoal/black — manganese oxides or dense carbon films.
• Greens — trace Cu/Cr or chlorite; uncommon but coveted.
• White/gray — clean chalcedony/agate fills.

“Rainbow” petrified wood (famously from Arizona) shows multiple iron states and mineral phases in bold, adjacent panels.

Pattern words

• Growth rings — light/dark bands marking seasonal growth.
• Rays — radial streaks (tree plumbing) from pith to bark.
• Vessel pores — in hardwoods; ring‑porous vs diffuse‑porous patterns.
• Knots & branch scars — swirl textures and figure.
• Agate veins — translucent banded silica healing cracks.
• Drusy pockets — sparkle‑lined cavities, little geode moments.

Photo tip: Side‑light around 30° makes rays pop and agate windows glow; a white bounce card opposite your light deepens color without glare.

Conifers (softwoods)

Mostly tracheids (long, uniform cells) with no vessels. Rays are typically narrow. Some show resin canals. Rings are often bold: wide earlywood (spring), narrow latewood (summer).

Hardwoods (angiosperms)

Vessels/pores are visible. Ring‑porous species have big pores at ring starts (oak/ash look); diffuse‑porous species distribute pores evenly (maple/poplar vibe). Rays may be wide and conspicuous.

Palm & monocots

Not true “wood”: look for scattered vascular bundles in a parenchyma background—dotted patterns (“palm root” or palmwood) rather than rings. Gorgeous, and diagnostic at a glance.

Color & inclusions

Hematite lines follow latewood; manganese paints dark rays; pale agate fills shrinkage cracks. Tiny drusy quartz may sparkle in voids—micro‑geodes where sap once flowed.

Species ID?

Possible to genus or family with good preservation, thin sections, and comparative anatomy. Many pieces are identified as “coniferous” or “hardwood” rather than a precise species.

Bonus clue

Check the bark: preserved outer rind with lenticels (pores) is a treat and confirms orientation (bark → cambium → wood).

Bog oak / subfossil wood

Dark, waterlogged wood (hundreds–thousands of years), still organic. Lightweight, wood smell when cut, burns. Petrified wood is stone‑heavy and will scratch glass.

Coal, jet, lignite

Carbon‑rich, soft relative to quartz; streaks dark; often dull to submetallic luster. Petrified wood is hard, vitreous on polish, and shows silica patterns.

Dye‑stained wood or resin casts

Repeating patterns or neon‑even color are red flags. Under a loupe, natural pieces show cellular anatomy, not printed grain.

Brecciated jasper

Can mimic angular “woody” patches, but lacks rays/rings. Petrified wood’s anatomy wins the tiebreaker under 10×.

Palm root vs. hardwood

Palm (monocot) shows speckled bundles without rings; hardwoods display pores + rings. Quick check with a hand lens settles it.

Checklist

• Stone‑heavy; scratches glass (quartz hardness).
• Visible rings/rays/pores arranged as wood anatomy.
• Agate/chalcedony luster; drusy pockets possible.

Classic places

Arizona, USA — Triassic logs of the Chinle Formation (“Rainbow” petrified wood). Yellowstone, USA — Eocene fossil forests entombed by volcanics. Washington State — Ginkgo Petrified Forest. Lesvos, Greece — Miocene ash‑preserved forest.

Global favorites

Madagascar — Triassic agatized wood with clear anatomy; Namibia — giant fossil trunks in desert settings; Indonesia — abundant silicified wood used for décor slabs; New Zealand (Curio Bay), Argentina (Patagonia) and beyond. Fossil forests are surprisingly cosmopolitan.

Everyday handling

• Quartz‑hard but still chip‑prone on sharp impacts—don’t test gravity.
• Large slabs are heavy: support evenly; felt pads protect shelves.

Cleaning

• Lukewarm water + mild soap + soft brush; rinse and dry.
• Avoid harsh abrasives; silica is tough, but polishes can haze.
• Iron films may lift with gentle chelating stone‑safe products; test inconspicuously.

Lapidary

• Orient cuts to show rings on face or rays in quartersawn views.
• Watch for hidden fractures; stabilize if needed before doming.
• Finish like agate: diamond → cerium/oxide polish; light pressure preserves crisp anatomy.

Ring reader

Use a loupe to follow growth rings across the slab. Count them and look for narrow “stress years.” You’re time‑traveling through the tree’s biography.

Agate windows

Back‑light thin edges: agate veins and chalcedony halos glow, while denser areas stay opaque. It’s a forest with stained‑glass moments.