Chert (Yellow Jasper variant)

Physical Properties

Hardness: 6.5–7 on Mohs scale; Color: Mustard yellow to golden brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (Microcrystalline quartz); Cleavage: None (Conchoidal fracture); Specific gravity: 2.6–2.7

Formation & Geological History

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation of silica from groundwater within sedimentary rock layers. This specimen shows a conchoidal fracture pattern typical of silica-rich rocks.

Uses & Applications

Historically used for making stone tools (knapping) such as scrapers and arrowheads. Currently used for lapidary work (jewelry, cabochons) and as a collector's specimen.

Geological Facts

Chert is so durable that it can remain unchanged for millions of years. This specific yellow color is often caused by the presence of iron oxide (goethite) inclusions within the silica matrix.

Field Identification & Locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is often found as nodules or layers within limestone or dolomite beds.

Identified on: 4/22/2026

Mode: Standard