sedimentary

Chert (Jasper/Carnelian variety)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Orange to reddish-brown (likely due to iron oxidation). Luster: Waxy to vitreous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Orange to reddish-brown (likely due to iron oxidation)
Luster: Waxy to vitreous

Identified July 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the accumulation of silica-rich fluids or biological remains (like radiolaria) in sedimentary basins, later solidifying into dense microcrystalline quartz. Often found in nodules within limestone or as stream-worn pebbles.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to conchoidal fracturing. Currently used in lapidary work, jewelry, and as decorative gravel.

Geological facts

Chert is one of the most durable rocks on the Earth's surface. When struck against steel, it can produce sparks, making it a primitive fire-starting tool. The reddish-orange color variants are often referred to as Jasper or Carnelian depending on translucency.

Field identification & locations

Identify by its waxy luster, extreme hardness (it will scratch glass), and its shell-like (conchoidal) curved breakage patterns. Commonly found in riverbeds and eroded sedimentary outcrops.

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Sandstone or Siltstone

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Fossiliferous Concretion

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Brown Sandstone (River Rock)

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Mudstone

Argillite / Siliciclastic sedimentary rock

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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