sedimentary
Chert (variously identified as Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale. Color: Gray, tan, and white with some veining. Luster: Waxy to dull. Structure: Non-crystalline mass (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6
- Hardness
- 6
- Color
- Gray, tan, and white with some veining
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Gray, tan, and white with some veining. Luster: Waxy to dull. Structure: Non-crystalline mass (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from groundwater. This piece appears to be a water-worn river stone or a tumbled fragment from a larger nodule, typically found in limestone or chalk deposits.
Uses & applications
Historically used for stone tools and starting fires (flint). Modernly used in landscaping, road aggregate, and sometimes as low-to-medium grade decorative stones for lapidary work.
Geological facts
Chert is so tough it was the primary material for prehistoric arrowheads and spear tips because it breaks into razor-sharp edges. It is chemically stable and resistant to weathering, which is why it is often found as smooth pebbles in riverbeds.
Field identification & locations
Identify in the field by its conchoidal (shell-like) fracture pattern and the fact that it will scratch glass. This specific specimen’s rounded edges and small size suggest it was collected from a gravel bed or river. Common worldwide.
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