sedimentary

Chert (likely jasper-bearing chert)

Microcrystalline quartz (SiO₂), with iron-oxide staining and possible chalcedony

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque to translucent brown, gray, black, and orange, with a dull to waxy luster and irregular conchoidal fracture. It lacks visible cleavage and is composed of extremely fine quartz crystals.

Identified August 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich sediment or biogenic silica (such as radiolarians or sponge remains) becomes cemented and recrystallized, commonly within marine limestone or volcanic sediment. Its exact age cannot be determined from the image and may range from Precambrian to recent.

Uses & applications

Used historically for sharp tools and arrowheads; attractive jasper varieties are cut for cabochons, beads, carvings, and decorative stone. Ordinary chert has limited commercial value.

Geological facts

The orange and red colors typically come from hematite or limonite, while dark gray areas may reflect carbonaceous matter or finely dispersed minerals. Conchoidal fracture and edge sharpness are characteristic.

Field identification & locations

Identify it by its very fine texture, lack of visible grains, waxy surface, conchoidal fracture, and ability to scratch ordinary glass. Common worldwide, especially in sedimentary formations; likely worth about $5–$25 as a rough hand specimen, or $20–$75 if unusually colorful and polished.