Petrified Wood (Calamites Fossil)

Physical Properties

Hardness: 6.5-7 (Mohs scale), Color: Dark grey to charcoal black with earthy brown highlights, Luster: Dull to waxy, Structure: Ribbed or grooved longitudinal pith cast texture, Cleavage: None (conchoidal fracture when broken)

Formation & Geological History

Formed through permineralization of Carboniferous era (approx. 300 million years ago) giant horsetail plants. Organic matter was replaced by silica and other minerals in low-oxygen swamp environments.

Uses & Applications

Used primarily as decorative collector specimens, scientific study of paleo-botany, and sometimes cut into cabochons for jewelry.

Geological Facts

Calamites was a genus of giant treelike horsetails that grew to heights of over 30 meters. They were major contributors to the coal beds of the Carboniferous period.

Field Identification & Locations

Identify in the field by looking for distinct vertical ribbing or grooves that resemble modern horsetails but on a much larger scale. Commonly found in coal-bearing shale and sandstone layers in regions like the Appalachian Mountains and the UK.

Identified on: 4/20/2026

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