sedimentary

Chert Nodule

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 6
Color: Tan, beige, brown
Luster: Waxy to dull

Identified July 21, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed through the replacement of carbonate minerals by silica-rich fluids within limestone or chalk beds, or as primary chemical precipitates. They often dates back to various geological eras depending on the host rock.

Uses & applications

Used historically for stone tools due to sharp edges; currently used for landscaping, road construction aggregate, and as a collector's specimen.

Geological facts

Chert nodules often form around organic nuclei like sponges or shells. Because of its extreme hardness and resistance to weathering, chert often remains after the surrounding limestone has eroded away.

Field identification & locations

Identify by its 'knobby' or irregular rounded shape and its ability to scratch glass. It often has a weathered white or tan outer 'cortex' and is commonly found in gravel pits or limestone outcrops.