sedimentary

Chert / Microcrystalline Quartz

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically tan, gray, or brown; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: typically tan, gray, or brown
Luster: waxy to dull

Identified May 27, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically tan, gray, or brown; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. Common in limestone and chalk beds.

Uses & applications

Historically used for stone tools and arrowheads; currently used in construction aggregate and as a decorative stone in landscaping.

Geological facts

Because it breaks with a conchoidal fracture like glass, it creates very sharp edges, making it the primary material for prehistoric tools and weapons.

Field identification & locations

Identify by its waxy luster, hardness (will scratch glass), and shark-like shell-shaped fracture patterns. It is one of the most common rocks found in riverbeds and gravel pits.