sedimentary

Chert / Microcrystalline Quartz

Chert (SiO2)

Hardness: 7 (Mohs scale); Color: Light tan, grey, or greenish hues; Luster: Dull to waxy; Crystal structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None, exhibits conchoidal (shell-like) fracture; Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Light tan, grey, or greenish hues
Luster: Dull to waxy

Identified June 1, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed as a chemical precipitate from silica-rich fluids or the accumulation of siliceous remains of marine organisms (like radiolaria or diatoms) in deep-ocean settings. This specimen appears to be a weathered river stone or glacial pebble.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges; currently used for road base, landscaping, and as a low-cost lapidary material for tumbling.

Geological facts

Chert has been used by humans for millions of years to make fire and tools. It is so hard that it can scratch steel. Some varieties, like flint, are functionally the same but occur in chalk or limestone beds.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), conchoidal fracture patterns (curved break surfaces), and smooth, waxy texture when freshly broken. Found globally in sedimentary basins and stream beds.