sedimentary
Petrified Wood
Silicified Wood (SiO2 - Quartz/Chalcendony replacing organic matter)
Hardness: 6.5–7 on Mohs scale. Color: Highly variable, featuring reds, browns, oranges, and blacks (due to iron and manganese). Luster: Vitreous to waxy. Crystal Structure: Cryptocrystalline (Microcrystalline quartz). Cleavage: None; exhibits conchoidal fracture.
- Hardness
- 6
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Highly variable, featuring reds, browns, oranges, and blacks (due to iron and manganese). Luster: Vitreous to waxy. Crystal Structure: Cryptocrystalline (Microcrystalline quartz). Cleavage: None; exhibits conchoidal fracture.
Formation & geological history
Formed through permineralization over millions of years (often Triassic or Jurassic periods). Organic matter is buried under sediment where volcanic ash provides silica. Groundwater dissolves the organic material, replacing it with minerals like quartz or chalcedony. Total process takes 5 to 100 million years.
Uses & applications
Commonly used for decorative lapidary work, high-end furniture (slabs), jewelry (cabochons), and as museum or collector display specimens.
Geological facts
Famous locations include the Petrified Forest National Park in Arizona. In some cases, the replacement is so precise that the internal cellular structure of the original tree and wood grain is visible under a microscope.
Field identification & locations
Identify in the field by looking for a 'bark-like' exterior texture with a dense, heavy, stony interior that breaks like glass. Commonly found in arid landscapes where ancient riverbeds or volcanic ash layers are exposed, such as the American Southwest, Argentina, and Madagascar.
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