sedimentary
Chert (Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Brown, tan, reddish, or grey, Luster: Waxy to dull, Crystal Structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown, tan, reddish, or grey, Luster: Waxy to dull, Crystal Structure: Hexagonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains such as radiolaria or diatoms on the ocean floor, or via chemical precipitation from ground fluids. Typically dates from various eras, commonly found in limestone or chalk beds.
Uses & applications
Used historically for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as a durable lapidary material.
Geological facts
Small nodules of chert were the primary material for arrowheads and spear points due to their predictable conchoidal fracture which creates razor-sharp edges.
Field identification & locations
Identify in the field by its smooth, waxy surface and its tendency to break into sharp curved flakes. It is very hard and will scratch glass and steel. Found globally in sedimentary environments.
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