sedimentary

Chert (and Agate/Chalcedony)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: Variegated brown, gray, and translucent white, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6

Hardness: 6

Identified June 21, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Variegated brown, gray, and translucent white, Luster: Waxy to vitreous, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6

Formation & geological history

Formed through the accumulation of silica-rich fluids in limestone or volcanic cavities. These specimens appear to be flint/chert nodules or agate-bearing geodes pieces found in sedimentary layers or alluvial deposits.

Uses & applications

Historically used for stone tools (arrowheads) due to conchoidal fracture. Today used for lapidary work, jewelry (especially the translucent agate portions), and as landscaping stone.

Geological facts

The sharp edges visible on some fragments demonstrate the rock's ability to break into blades, a property that made it the primary material for prehistoric survival tools.

Field identification & locations

Look for a waxy texture and shell-like (conchoidal) curves where the rock has broken. It is harder than steel and will scratch glass. Common in riverbeds and limestone outcrops.