sedimentary

Chert (Yellow Jasper)

Cryptocrystalline Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: mustard yellow to brownish-orange; Luster: waxy to dull; Breakage: prominent conchoidal fracture with sharp edges; Crystal structure: Microcrystalline/Cryptocrystalline quartz.

Hardness: 6
Color: mustard yellow to brownish-orange
Luster: waxy to dull

Identified July 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in sedimentary environments through the accumulation of silica-rich microfossils (like radiolarians) or by the direct chemical precipitation of silica from groundwater within limestone or chalk beds.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges. Modernly used for landscaping, as a gemstone in tumbled jewelry, and for flint-knapping enthusiasts.

Geological facts

Often called 'Jasper' when opaque and yellow/red/brown. It is extremely durable and weather-resistant, which is why it is often found as loose stones in riverbeds long after the surrounding rock has eroded.

Field identification & locations

Identify in the field by its waxy texture, smooth curved (conchoidal) breaks, and the fact that it is hard enough to scratch glass. Found globally, especially in areas with limestone deposits.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary