sedimentary

Chert (often called Flint when dark)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray, green, or black with waxy luster; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Gray, green, or black with waxy luster

Identified May 9, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray, green, or black with waxy luster; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation in marine environments and limestone beds. Prevalent in Paleozoic to Mesozoic strata.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in road surfacing, fire-starting kits (flint and steel), and as a gemstone when colorful (Jasper).

Geological facts

Because of its conchoidal fracture, it breaks into razor-sharp edges, making it the most important material for prehistoric humans to create survival tools.

Field identification & locations

Identify in the field by its very smooth, waxy surface and curved, glass-like fracture (conchoidal). It is extremely hard and will scratch glass easily.