sedimentary

Chert Nodules in Limestone

Microcrystalline Quartz (SiO2) in Carbonate Matrix

AI-generated identification · may be incorrect

Hardness: 7 (chert), 3 (limestone matrix); Color: Dark grey to black interior with light grey rim; Luster: Waxy to vitreous on fresh break; Cleavage: None (conchoidal fracture)

Hardness: 7 (chert), 3 (limestone matrix)
Color: Dark grey to black interior with light grey rim
Luster: Waxy to vitreous on fresh break

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 7 (chert), 3 (limestone matrix); Color: Dark grey to black interior with light grey rim; Luster: Waxy to vitreous on fresh break; Cleavage: None (conchoidal fracture)

Formation & geological history

Formed through the precipitation of silica within marine carbonate sediments. Often originates from the dissolution of siliceous organisms like sponges or radiolarians during diagenesis.

Uses & applications

Historically used for making stone tools (flintknapping) due to its sharp edges; used in construction aggregate and as a specimen for geological study.

Geological facts

Dark chert like this is often referred to as 'flint' in archaeological contexts. The light outer layer is a 'weathering rind' or 'cortex' caused by the leaching of minerals over time.

Field identification & locations

Identify by its conchoidal (glass-like) fracture and high hardness relative to the surrounding limestone. It will scratch glass easily. Commonly found in limestone outcrops and riverbeds.