Chert (and Petrified Wood)

Physical Properties

Hardness: 7.0 (Mohs). Color: Tan, white, and translucent gray. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & Geological History

Formed through the replacement of organic material (likely wood fiber) by silica-rich groundwater. This specimen displays a fibrous/woody texture indicative of permineralization, typically occurring in ancient volcanic ash or fluvial deposits.

Uses & Applications

Historically used for stone tools due to its sharp edges. Today used in landscape decor, lapidary arts, and as geological collector specimens.

Geological Facts

This specimen appears to be a fragment of petrified wood consisting of chert/chalcedony. It preserves the original cellular structure of the plant while being completely replaced by minerals over millions of years.

Field Identification & Locations

Identify in the field by its hardness (scratches glass), waxy feel, and the preservation of fibrous or grain-like patterns reminiscent of wood. Commonly found in areas with historic volcanic activity or sedimentary basins like the Petrified Forest in Arizona.

Identified on: 5/11/2026

Mode: Standard