sedimentary
Chert (Iron-stained)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale. Color: Cream, white, and tan with reddish-orange iron oxide staining. Luster: Waxy to dull. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Cream, white, and tan with reddish-orange iron oxide staining. Luster: Waxy to dull. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or via chemical precipitation from silica-rich fluids in limestone/dolomite cavities. This specimen appears to be a nodule or vein formation within a host matrix.
Uses & applications
Historically used for stone tools (arrowheads and scrapers) due to its sharp conchoidal fracture. Modern uses include construction aggregate, road surfacing, and as a decorative landscaping stone or tumbled pocket stone for collectors.
Geological facts
Chert is so durable that it often remains in the soil long after its surrounding limestone host rock has weathered away. It is chemically identical to quartz but contains microscopically small crystals that give it its opaque, waxy appearance.
Field identification & locations
Identify in the field by its hardness (it will scratch glass/steel) and its distinctive shell-like (conchoidal) breakage patterns. Often found in creek beds or eroding out of limestone cliffs. Common globally, especially in the Midwestern and Southeastern United States.
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