fossil

Fossilized Wood (Petrified Wood) and Associated Rocks

Silicified Wood / Xylopal

Hardness of 6.5 to 7 on the Mohs scale; colors range from brown, gray, and tan to multicolored hues; luster is vitreous to waxy; crystal structure is microcrystalline quartz (chalcedony/jasper); no true cleavage; specific gravity around 2.5 to 2.8.

Identified July 28, 2026More fossil →

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Physical properties

Formation & geological history

Formed when organic plant material is buried in an oxygen-free environment by sediment, preventing decay. Over millions of years, groundwater rich in dissolved minerals (mainly silica) flows through the sediment and replaces the organic matter molecule by molecule with quartz, preserving the original cellular structure. Ages range widely from Triassic to Cenozoic.

Uses & applications

Used for lapidary work, making decorative items, bookends, jewelry, tabletops, and highly prized by rockhounds and fossil collectors.

Geological facts

Petrified wood can retain microscopic details of the original tree's rings and cell walls. The Petrified Forest National Park in Arizona is one of the most famous occurrences in the world.

Field identification & locations

Identified in the field by its distinct tree-ring or bark-like exterior texture combined with a heavy, stone-like feel and conchoidal fracture typical of quartz. Found worldwide in ancient sedimentary layers, riverbeds, and desert regions.

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Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

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Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

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Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

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Fossiliferous Limestone

Limestone with embedded fossil cross-section

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Fossiliferous Limestone

Fossiliferous Calcilutite / Biomicrite

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