sedimentary
Chert (Cream Variety)
Microcrystalline silica (SiO2)
Hardness: 7 Mohs, Color: Cream/Tan/White, Luster: Waxy to dull, Crystal structure: Hexagonal (cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6
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Physical properties
Hardness: 7 Mohs, Color: Cream/Tan/White, Luster: Waxy to dull, Crystal structure: Hexagonal (cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6
Formation & geological history
Formed in marine environments through the precipitation of silica from seawater or the accumulation of siliceous skeletal remains (like diatoms) on the seafloor. It often forms as nodules or bedded layers within limestone or chalk.
Uses & applications
Historically used for stone tools (knapping) like arrowheads and scrapers due to its sharpness. Modernly used in construction aggregate, road base, and as decorative gravel. High-purity versions may be used for jewelry or lapidary arts.
Geological facts
Chert is essentially the same mineral as flint and jasper; the names vary based on color and context. It is so hard that it can scratch steel and was used for centuries to start fires by striking it against iron.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is common worldwide, particularly in limestone-rich regions like the American Midwest or the UK.
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