Chert (Jasper variety)

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Brown, reddish-brown, tan; Luster: Dull to waxy (looks vitreous when wet); Crystal Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids in sedimentary basins. This specimen shows significant rounding, suggesting it was transport by water (alluvial) in a riverbed.

Uses & Applications

Historically used for stone tools due to sharp edges; currently used for lapidary work (cabochons), landscaping, and as a collector's item.

Geological Facts

Jasper is an opaque variety of chert. Because of its extreme hardness and durability, it often survives long-distance transport in rivers and remains largely intact while softer rocks erode away.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass), its smooth 'waxy' texture, and its characteristic conchoidal (shell-like) fracture patterns. Frequently found in gravel bars of rivers and along coastlines.

Identified on: 4/28/2026

Mode: Standard