sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, and gray. Luster: Vitreous to waxy. Crystal Structure: Hexagonal (microcrystalline). Cleavage: None, conchoidal fracture. Specific Gravity: 2.6-2.9.

Hardness: 6
Color: Brown, tan, and gray
Luster: Vitreous to waxy

Identified June 22, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, and gray. Luster: Vitreous to waxy. Crystal Structure: Hexagonal (microcrystalline). Cleavage: None, conchoidal fracture. Specific Gravity: 2.6-2.9.

Formation & geological history

Formed through permineralization, a process where organic material is replaced by minerals (primarily silica) over millions of years, often in volcanic ash beds or river sediments. Most specimens are from the Mesozoic or Cenozoic eras.

Uses & applications

Used for jewelry (cabochons), lapidary art, home decor (bookends, furniture), and as educational or collector specimens.

Geological facts

Petrified wood is the state gem of Washington and the state fossil of Arizona. The cell structure of the original tree is often preserved so well that the species of the tree can be identified under a microscope.

Field identification & locations

Identified by wood-grain patterns, bark-like textures, and high hardness (cannot be scratched by a steel knife). Commonly found in the western United States, Madagascar, and Brazil. Always look for cellular patterns.