sedimentary

Chert (Jasper/Limonitic Chert)

Microcrystalline Quartz (SiO2)

Hardness: 6.5–7 (Mohs scale); Color: Yellowish-brown to tan (due to limonite/iron inclusion); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7

Hardness: 6
Color: Yellowish-brown to tan (due to limonite/iron inclusion)
Luster: Waxy to dull

Identified April 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich fluids in sedimentary basins or the replacement of limestone. This specimen likely formed during the Paleozoic or Mesozoic eras in a marine environment where silica replaced organic material or carbonate minerals.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to conchoidal fracture. Modern uses include decorative gravel, landscaping, and lapidary work (polishing for jewelry as 'yellow jasper').

Geological facts

Chert is so hard it can scratch steel and was used alongside flint by ancient civilizations to start fires by striking it against iron pyrite or steel to create sparks.

Field identification & locations

Identify in the field by its characteristic 'shell-like' shell-like conchoidal fracture patterns and extreme hardness (will not be scratched by a knife). Commonly found in riverbeds or within limestone outcrops.

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