sedimentary
Chert (Nodule)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: typically gray, brown, or tan with a waxy or dull luster; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 6
- Color
- typically gray, brown, or tan with a waxy or dull luster
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: typically gray, brown, or tan with a waxy or dull luster; Structure: microcrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the precipitation of silica from groundwater in the pore spaces of sedimentary rocks or through the accumulation of siliceous skeletal remains of marine organisms such as diatoms and radiolarians.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers); currently used in road construction, and occasionally for lapidary work if it exhibits attractive colors or patterns (Jasper).
Geological facts
Chert is chemically very similar to flint, but flint is usually found in chalk or marly limestone. It is one of the most durable rocks and can spark when struck against steel.
Field identification & locations
Identify in the field by its very hard surface (will scratch glass), a smooth/waxy feel, and sharp, shell-like (conchoidal) edges when broken. It is extremely common in limestone regions worldwide.
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