sedimentary

Chert (often called Flint or Jasper when pigmented)

Microcrystalline or cryptocrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: tan, yellow, orange-brown (due to iron oxide staining); Luster: dull to waxy; Crystal structure: hexagonal (microscopic); Cleavage: none, exhibits prominent conchoidal fracture; Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: tan, yellow, orange-brown (due to iron oxide staining)
Luster: dull to waxy

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from groundwater within limestone/chalk beds. These specimens often originate from the Paleozoic or Mesozoic eras.

Uses & applications

Abrasives, historical tool-making (arrowheads, scrapers), landscaping stone, and occasionally used in jewelry as 'Jasper' when showing vivid colors.

Geological facts

Because it breaks with sharp, shell-like edges (conchoidal fracture), it was the primary material used by prehistoric humans for stone tools and weapons. It is chemically very stable and resistant to weathering.

Field identification & locations

Identify in the field by its superior hardness (cannot be scratched by a steel knife) and its smooth, curved fracture surfaces. Found worldwide in sedimentary basins, riverbeds, and as nodules in limestone outcrops.

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Brecciated Chert (Microcrystalline Silica)

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