Chert / Jasper

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Variegated brown, tan, and reddish-orange; Luster: Waxy to vitreous (especially when wet); Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the accumulation of silica-rich microfossils or chemical precipitation from hydrothermal fluids in sedimentary environments. Common in marine or lake deposits from various geological eras, including Paleozoic to Cenozoic.

Uses & Applications

Historically used for stone tools (knapping); modernly used for lapidary work, decorative landscaping, and as river rock. Polished specimens are used in jewelry.

Geological Facts

This specimen appears to be a 'river rock' or 'glacial cobble' that has been naturally smoothed by water. The reddish tints indicate iron oxide inclusions within the silica matrix.

Field Identification & Locations

Identify in the field by its hardness (it should scratch glass), waxy appearance, and conchoidal (shell-like) fracture edges. These are ubiquitous in riverbeds and glacial tills across North America and Europe.

Identified on: 4/21/2026

Mode: Standard