sedimentary

Chert Nodules (with Gryphaea or Shell inclusions)

Microcrystalline Quartz (SiO2) with Calcitic inclusions

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, off-white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Gray, tan, off-white
Luster: Waxy to dull

Identified May 18, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, off-white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed primarily in marine environments through the replacement of limestone or carbonate sediment by silica-rich fluids. Often contains fossilized remnants ranging from the Mesozoic or Cenozoic eras.

Uses & applications

Used historically for stone tools and strike-a-lights. Today primarily of interest to hobbyist collectors and used as garden decoration or road aggregate.

Geological facts

This specimen appears to be a weathered beach pebble of chert or flint containing fossilized shell fragments, possibly 'Devil\u0027s Toenails' (Gryphaea) which were common in ancient shallow seas.

Field identification & locations

Identify by its hardness (it will scratch glass) and smooth, rounded surface indicating water wear. Commonly found on beaches and in riverbeds where limestone bedrock is present.