sedimentary

Chert (Agate/Flint variant)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs); Color: Banded grey, white, and tan; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 (Mohs)
Color: Banded grey, white, and tan
Luster: Waxy to vitreous

Identified April 11, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs); Color: Banded grey, white, and tan; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation from hydrothermal fluids in sedimentary basins. The banding indicates rhythmic deposition or replacement processes over millions of years.

Uses & applications

Used historically for stone tools due to its sharp edges. Modern uses include home decor, landscaping, and lapidary work (jewelry and polishing).

Geological facts

This specimen shows distinct 'swirly' banding common in agates. Chert is so hard it can easily scratch glass and even some steels. It was the primary material for arrowheads and scrapers in many ancient cultures.

Field identification & locations

Identify in the field by its waxy texture and shell-like (conchoidal) fracture patterns when broken. It is commonly found in limestone or chalk deposits and as stream-rounded cobbles.