sedimentary
Chert (Flint)
Chert (Cryptocrystalline Silica, SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and brown with distinct banding; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and brown with distinct banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and brown with distinct banding; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or through chemical precipitation in marine environments; often occurs as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools (knapping) and fire-starting; currently used in construction aggregate, road surfacing, and as a semi-precious stone for lapidary work.
Geological facts
Chert has a conchoidal fracture that produces very sharp edges, which made it the primary material for prehistoric arrowheads and spear points. Banded varieties like this one are sometimes referred to as 'striped flint'.
Field identification & locations
Identify by its hardness (scratches glass), waxy texture, and shell-like (conchoidal) curved break patterns. Commonly found in riverbeds or eroding out of sedimentary rock layers.
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