sedimentary

Banded Chert / Flint

Silicon dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Black, gray, and yellow/tan bands; Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Black, gray, and yellow/tan bands
Luster: Waxy to dull

Identified April 10, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Black, gray, and yellow/tan bands; Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.65

Formation & geological history

Formed as chemical precipitates from silica-rich fluids in ocean or lake sediments. These layers represent varying mineral impurities during deposition, often millions of years old (Paleozoic to Mesozoic era). This specific specimen shows river-worn tumbling, giving it a smooth, pebble-like surface.

Uses & applications

Historically used for stone tools and starting fires (striking steel). In modern times, used for lapidary work, jewelry (cabochons), and as landscaping stone. Polished specimens are popular with collectors.

Geological facts

Chert and flint are essentially the same material; the name 'flint' is often reserved for dark gray or black nodules found in chalk or limestone. Highly valued by ancient humans for its ability to produce razor-sharp edges.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture pattern. It often feels 'slicker' or waxier than other surrounding rocks. Frequently found in riverbeds or coastal rocky beaches.