Red Chert

Physical Properties

Hardness: 7 (Mohs scale), Color: Red to brownish-red, Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed from the accumulation of silica-rich organic remains, such as radiolaria or diatoms, in deep-sea environments. Often found in Precambrian to Mesozoic rock layers.

Uses & Applications

Historically used for making stone tools (arrowheads, scrapers) due to conchoidal fracture. Currently used in landscaping, as a gemstone (Jasper), and for industrial abrasives.

Geological Facts

Red chert is often colored by iron oxide impurities. The famous 'Ribbon Chert' of the Marin Headlands in California is a prime example of this rock's formation in ancient seabed conditions.

Field Identification & Locations

Identify by its extreme hardness (scratches glass), waxy feel, and sharp, shell-like (conchoidal) edges when broken. Commonly found in bedded deposits within oceanic sedimentary sequences.

Identified on: 4/27/2026

Mode: Standard