sedimentary
Chert (Agate/Flint variant)
Microcrystalline Quartz (SiO2)
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
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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.
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