sedimentary
Chert (Jasper/Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness 6.5-7 (Mohs scale); Color ranges from brown to yellowish-tan; Luster is waxy to vitreous; Crystal structure is trigonal (microcrystalline); Conchoidal fracture with sharp edges; Specific gravity 2.6-2.65.
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Physical properties
Hardness 6.5-7 (Mohs scale); Color ranges from brown to yellowish-tan; Luster is waxy to vitreous; Crystal structure is trigonal (microcrystalline); Conchoidal fracture with sharp edges; Specific gravity 2.6-2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation from silica-rich fluids in sedimentary basins. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp fracture; currently used for lapidary work, jewelry, and as a decorative stone.
Geological facts
Chert is one of the most durable sedimentary rocks. It was the primary material for the 'Stone Age' technology because it fractures like glass to create razor-sharp edges.
Field identification & locations
Identify in the field by its waxy texture, smooth conchoidal (shell-like) fracture, and its ability to scratch glass. Common in river beds and sedimentary outcrops globally.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Shale or Slaty Mudstone
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Sandstone
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