sedimentary

Chert / Chalcedony Nodules

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale); Color: Gray, blue-gray, brown, tan; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6

Hardness: 6
Color: Gray, blue-gray, brown, tan
Luster: Waxy to vitreous

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Gray, blue-gray, brown, tan; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed through the accumulation of silica-rich fluids within sedimentary rock layers, often limestone or chalk. These nodules typically precipitate from groundwater in voids or as replacements for original organic material over millions of years.

Uses & applications

Used historically for stone tools (knapping) due to its conchoidal fracture. Currently used for lapidary work, decorative landscaping, and as a component in some industrial abrasives.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most important materials for early humans to create arrowheads, scrapers, and blades because it breaks with razor-sharp edges.

Field identification & locations

Identify in the field by its waxy appearance on fresh surfaces, distinctive curved (conchoidal) fractures, and its ability to spark when struck with steel. Commonly found in gravel beds or weathered out of carbonate rock formations.