Petrified Wood

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, gray, black, sometimes red; Luster: Waxy or dull; Crystal Structure: Cryptocrystalline (usually chalcedony or opal); Cleavage: None; Specific Gravity: 2.58-2.91

Formation & Geological History

Formed through permineralization where organic plant material is replaced by minerals, typically silica, while buried under sediment or volcanic ash. This specimen likely dates to the Mesozoic or Cenozoic era.

Uses & Applications

Used for jewelry (cabochons), interior decoration (tables, bookends), and as a popular collector's item due to its fossil nature.

Geological Facts

Petrified wood is the state fossil of several US states. In the Petrified Forest National Park in Arizona, massive logs from the Triassic period have turned completely to quartz.

Field Identification & Locations

Identify by looking for visible wood grain, bark textures, or growth rings in a heavy, stony material. It is commonly found in sedimentary basins and areas with historical volcanic activity.

Identified on: 5/2/2026

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