Rock Identifier
Petrified Wood (Silicified Wood (SiO2)) — Mineral / Fossil
Mineral / Fossil

Petrified Wood

Silicified Wood (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5–7 (Mohs scale). Color: Earthy tones (brown, yellow, red, orange) from iron oxides. Luster: Waxy to vitreous when polished. Crystal structure: Cryptocrystalline (Microcrystalline) quartz replacing organic matter. Cleavage: None, exhibits conchoidal fracture. Specific Gravity: 2.6–2.9.

Hardness
6
Color
Earthy tones (brown, yellow, red, orange) from iron oxides
Luster
Waxy to vitreous when polished
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Physical properties

Hardness: 6.5–7 (Mohs scale). Color: Earthy tones (brown, yellow, red, orange) from iron oxides. Luster: Waxy to vitreous when polished. Crystal structure: Cryptocrystalline (Microcrystalline) quartz replacing organic matter. Cleavage: None, exhibits conchoidal fracture. Specific Gravity: 2.6–2.9.

Formation & geological history

Formed via permineralization, where organic wood material is replaced by minerals (primarily silica) over millions of years after being buried in sediment/volcanic ash. Geological age ranges from the Paleozoic to the Cenozoic, commonly from the Triassic period (approx. 225 million years ago).

Uses & applications

Used in ornamental jewelry (cabochons), lapidary arts, high-end furniture (slabs for tabletops), and as decorative display specimens for collectors.

Geological facts

Petrified wood is the state stone of Washington and the state fossil of Arizona. The organic cellulose is replaced atom-by-atom by silica, often preserving the wood's microscopic cellular structure so perfectly that tree rings and bark patterns remain visible.

Field identification & locations

Identify in the field by looking for distinct wood grain patterns, growth rings, or bark textures on the exterior of a rock that feels much heavier and harder than wood. Commonly found in Arizona (Petrified Forest National Park), Oregon, Madagascar, and Indonesia. Collectors check for conchoidal fractures (glassy chips) on broken edges.

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Other mineral / fossil specimens

Petrified Wood / Fossilized Bone (Silicified / Mineralized Fossil (Silica SiO2)) — fossil

Petrified Wood / Fossilized Bone

Silicified / Mineralized Fossil (Silica SiO2)

fossil
Fish Fossil in Limestone (Lycoptera (likely) in Micritic Limestone) — sedimentary

Fish Fossil in Limestone

Lycoptera (likely) in Micritic Limestone

sedimentary
Weathered quartz-rich rock or fossil fragment (Indeterminate; likely quartz-bearing sandstone or siliceous fossil material) — mineral

Weathered quartz-rich rock or fossil fragment

Indeterminate; likely quartz-bearing sandstone or siliceous fossil material

mineral
Weathered quartz-rich rock fragment (Likely quartz-bearing sandstone or granitic rock; exact identification is uncertain from the image) — mineral

Weathered quartz-rich rock fragment

Likely quartz-bearing sandstone or granitic rock; exact identification is uncertain from the image

mineral
Likely weathered iron-rich pebble (brown sandstone or ironstone) (Indeterminate ferruginous sandstone/ironstone; commonly quartz (SiO₂) with iron oxides such as goethite and hematite) — sedimentary

Likely weathered iron-rich pebble (brown sandstone or ironstone)

Indeterminate ferruginous sandstone/ironstone; commonly quartz (SiO₂) with iron oxides such as goethite and hematite

sedimentary
Light-gray river pebble (Indeterminate; likely fine-grained quartz-rich rock such as quartzite or pale granite) — igneous

Light-gray river pebble

Indeterminate; likely fine-grained quartz-rich rock such as quartzite or pale granite

igneous