Chert (Jasper/Ironstone variety)

Physical Properties

Hardness: 6.5-7 Mohs scale; Color: Reddish-brown, earthy tan; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Frequently found in Precambrian and Paleozoic formations, often enriched with hematite or goethite giving it the brown-red hue.

Uses & Applications

Historically used for stone tools and arrowheads; currently used as landscaping stone, construction aggregate, and occasionally as lapidary material for polishing.

Geological Facts

Chert is so durable that it often survives long after the surrounding rock has weathered away. The reddish-brown colors are usually a result of trace amounts of iron oxidation within the silica matrix.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass), its smooth, shell-like (conchoidal) fracture surfaces, and its lack of visible grains. Found worldwide in riverbeds and limestone outcrops.

Identified on: 5/4/2026

Mode: Standard