mineral (silicate-replaced organic material)
Petrified Wood
Silicified wood (primarily Silicon Dioxide - SiO2)
Hardness: 6.5 to 7 on Mohs scale; Color: typically browns, grays, and tans with visible grain; Luster: vitreous to waxy (smooth when polished); Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: approx. 2.6.
- Hardness
- 6
- Color
- typically browns, grays, and tans with visible grain
- Luster
- vitreous to waxy (smooth when polished)
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Physical properties
Hardness: 6.5 to 7 on Mohs scale; Color: typically browns, grays, and tans with visible grain; Luster: vitreous to waxy (smooth when polished); Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: approx. 2.6.
Formation & geological history
Formed through permineralization, where organic remains are buried under sediment or volcanic ash. Groundwater rich in dissolved solids (usually silica) flows through the sediment, replacing plant material with stone over millions of years. This specimen likely dates from the Triassic to the Paleogene periods.
Uses & applications
Primarily used as decorative display specimens, for jewelry (cabochons), and in lapidary work. Polished slabs are high-value collector items.
Geological facts
In petrified wood, the replacement process is often so precise that cellular-level details like growth rings and bark textures are perfectly preserved. The Arizona Petrified Forest is the world's most famous locality for these specimens.
Field identification & locations
Identify in the field by searching for 'stony' rocks that retain the visual patterns of wood grain, tree rings, or bark. It is significantly heavier than living wood and cold to the touch. Commonly found in areas with sedimentary basins, such as the American Southwest, Madagascar, and Indonesia.
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