Jasper and Basalt (Mixed Breccia or Chert)

Physical Properties

Hardness: 6.5-7 (Mohs scale), Color: dull red, gray-blue, and earthy brown, Luster: dull to waxy, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.9

Formation & Geological History

Formed through the infiltration of silica into volcanic rocks or the deposition of silica-rich marine sediments. This specimen shows a mix of microcrystalline quartz (Jasper/Chert) with an underlying volcanic base (Basalt or Andesite), likely colored by iron oxides.

Uses & Applications

Used primarily for landscape decoration, lapidary work (cabochons), and historical tool-making (stone blades). Larger quantities are used in construction as fill or aggregate.

Geological Facts

This specimen appears to be a 'chert' or 'jasperoid' nodule with a weathered rind. Such rocks were highly prized by early humans for their predictable fracture patterns, allowing them to be knapped into sharp tools and spearheads.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like fracture pattern. Commonly found in riverbeds, desert pavements, and exposed volcanic layers globally, especially in Oregon, California, and the Midwestern US.

Identified on: 4/19/2026

Mode: Standard