sedimentary
Chert (Yellow Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness (7 on Mohs scale), Color: Opaque yellow to tan with brown rind, Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness (7 on Mohs scale), Color: Opaque yellow to tan with brown rind, Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the precipitation of silica-rich fluids or the accumulation of silica-based organic remains (like radiolaria) in sedimentary layers. It can also form during diagenesis in limestone or dolostone. Geological age ranges from Precambrian to Holocene.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges. Today used as an ornamental stone, in jewelry (cabochons), and as a landscaping material.
Geological facts
Chert was one of the first materials used by early humans to create fire-starting tools and weaponry because it fractures into extremely sharp, glass-like edges.
Field identification & locations
Identify in the field by its waxy texture, smooth conchoidal (shell-like) fracture patterns, and its ability to scratch glass. Commonly found in riverbeds, glacial tills, and as nodules in limestone outcrops.
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