sedimentary

Chert (Yellow/Tan variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, yellow, or mustard; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, yellow, or mustard
Luster: Waxy to dull

Identified May 6, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, yellow, or mustard; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolarians or diatoms) in marine environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Used historically for stone tools due to its sharp edges; currently used in decorative landscaping, construction aggregate, and occasionally tumbled for lapidary use.

Geological facts

Chert is nearly identical to flint, but 'flint' is usually reserved for dark grey or black varieties found in chalk. It is chemically very stable and resistant to weathering.

Field identification & locations

Identify by its 'waxy' texture and conchoidal (shell-like) fracture patterns. It will easily scratch glass and does not react with acid. Commonly found in riverbeds and coastal areas where sedimentary layers have eroded.