sedimentary

Chert (Carnelian/Jasper variety)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Orangey-brown to reddish-brown; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Orangey-brown to reddish-brown
Luster: Waxy to vitreous

Identified July 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily through the precipitation of silica from groundwater or the accumulation of silica-rich organic remains in sedimentary basins. The color is typically derived from iron oxide impurities.

Uses & applications

Used historically for stone tools and weapons due to its conchoidal fracture. In modern times, it is used for lapidary work, jewelry (cabs), and as a decorative landscaping stone.

Geological facts

This specimen displays classic conchoidal (shell-like) fracturing, which was a vital property for prehistoric humans to create sharp edges on arrowheads and knives.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (scratches glass), and distinctive curved, glass-like fracture surfaces. Frequently found in stream beds or within limestone/chalk deposits.

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Sandstone or Siltstone

Arenite (if sandstone)

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Sandstone

Arenite (primarily SiO2)

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