sedimentary

Flint / Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Light grey with brown/tan patches. Luster: Waxy to vitreous. Crystal structure: Microcrystalline/cryptocrystalline quartz (chalcedony). Cleavage: None, exhibits characteristic conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 7 on Mohs scale
Color: Light grey with brown/tan patches
Luster: Waxy to vitreous

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions, or through the accumulation of siliceous skeletal remains of marine organisms diagenetically altered over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and firearm ignition mechanisms (flintlocks). Today primarily collected or used for decorative landscaping and occasional lapidary work.

Geological facts

Flint and chert are fundamentally the same material; 'flint' typically refers to the dark variety found in chalk deposits, while 'chert' is found in limestone. Its sharp conchoidal fracture made it one of the most important materials for early human toolmaking.

Field identification & locations

Easily identified by its smooth, water-worn or nodular exterior, waxy luster on freshly broken surfaces, high hardness (scratches glass), and sharp conchoidal fracture edges. Commonly found in riverbeds, glacial tills, and weathering out of limestone or chalk formations worldwide.