sedimentary
Chert or Chalcedony
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs), Color: Grey, tan, brown, or white. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Grey, tan, brown, or white
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Grey, tan, brown, or white. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed by the accumulation of siliceous remains of organisms or the chemical precipitation of silica in sedimentary environments. Common in marine or lake deposits.
Uses & applications
Used in construction aggregates, road surfacing, or historically for stone tools due to sharp edges when fractured.
Geological facts
Ancient civilizations used this material to make arrowheads and spears because it fractures predictably into sharp blades.
Field identification & locations
Identified by its waxy luster, conchoidal fracture (curved like glass), and its ability to scratch glass. Found frequently in riverbeds or limestone outcrops.
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