sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness of 7 on the Mohs scale; colors vary from white, grey, brown to pale green or blue; vitreous to dull luster; cryptocrystalline structure; conchoidal fracture with sharp edges; specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; colors vary from white, grey, brown to pale green or blue; vitreous to dull luster; cryptocrystalline structure; conchoidal fracture with sharp edges; specific gravity around 2.60 to 2.65.
Formation & geological history
Formed through the chemical precipitation of silica from aqueous solutions or the accumulation of siliceous skeletal remains of marine organisms such as radiolarians and diatoms, typically during the Mesozoic and Paleozoic eras.
Uses & applications
Historically used for making stone tools, arrowheads, and blades due to its conchoidal fracture; occasionally used as decorative landscaping stone or in lapidary work.
Geological facts
Chert was one of the earliest materials utilized by early humans for tool-making because of the sharp, predictable edges it produces when fractured.
Field identification & locations
Can be identified in the field by its hardness (scratches glass), waxy to dull luster, and distinctive smooth conchoidal fracture. Commonly found within layers of limestone or chalk.
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