sedimentary

Chert (White-Tan variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on the Mohs scale. Color: Opaque white, tan, eggshell, or light gray. Luster: Dull to waxy. Crystal Structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Hardness: 7 on the Mohs scale
Color: Opaque white, tan, eggshell, or light gray
Luster: Dull to waxy

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or via chemical precipitation from silica-rich groundwater within limestone or chalk beds. Most specimens date from the Phanerozoic eon.

Uses & applications

Used historically for stone tools and arrowheads due to its sharp conchoidal edges; currently used for road ballast, concrete aggregate, and as landscaping stone.

Geological facts

Chert is so hard it can scratch steel and glass. Because it sparks when struck against steel, it was used in flintlock firearms. In its dark gray/black form, it is commonly called 'Flint.'

Field identification & locations

Identify it in the field by its very hard surface, waxy texture, and distinctive shell-like (conchoidal) curves where it breaks. Found worldwide in sedimentary rock outcrops, particularly where limestone is present.

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