sedimentary

Arrowhead (Flint/Chert)

Microcrystalline Quartz (SiO2)

Mohs hardness of 7, vitreous to waxy luster, conchoidal fracture, and typically dark gray to black coloration.

Identified October 30, 2026More sedimentary →

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Physical properties

Mohs hardness of 7, vitreous to waxy luster, conchoidal fracture, and typically dark gray to black coloration.

Formed through the chemical replacement of limestone or chalk by silica-rich groundwaters in marine environments over millions of years.

Historically used as a cutting tool and projectile point; currently collected as an artifact and ornamental specimen.

Knapped by ancient indigenous peoples using percussion and pressure flaking techniques to achieve sharp edges.

Identified by its distinct conchoidal fracture and human-crafted notches; commonly found in historical habitation sites and plowed fields.

Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion

Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Sandstone or Siltstone

Arenite (if sandstone)

Sandstone

Arenite

Shale

Shale (clastic sedimentary rock)

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)