sedimentary
Chert / Flint
Silicon Dioxide (Microcrystalline Quartz, $SiO_2$)
Hardness: 7 on Mohs scale; Color: Brownish-yellow (often called jasper or yellow chert), grey, white, black; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline / Cryptocrystalline; Cleavage: None, exhibits conchoidal fracture; Specific Gravity: 2.60 - 2.65
- Hardness
- 7 on Mohs scale
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Brownish-yellow (often called jasper or yellow chert), grey, white, black; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline / Cryptocrystalline; Cleavage: None, exhibits conchoidal fracture; Specific Gravity: 2.60 - 2.65
Formation & geological history
Formed through the chemical precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains of marine organisms (such as diatoms or radiolarians) within carbonate sedimentary sequences like limestone or chalk, often during the Mesozoic or Paleozoic eras.
Uses & applications
Historically used by early humans for making stone tools (arrowheads, scrapers, blades) due to its sharp conchoidal fracture. Modern uses include abrasives, road aggregate, and occasionally ornamental lapidary work.
Geological facts
Chert and flint are chemically identical; the term 'flint' is typically reserved for darker varieties found in chalk deposits, whereas 'chert' often refers to lighter-colored varieties found in limestone.
Field identification & locations
Easily identified in the field by its smooth, water-worn exterior often showing a distinct yellowish-brown weathered cortex, a waxy luster on freshly broken surfaces, and extremely sharp conchoidal fracture edges. Found worldwide in limestone and chalk regions.
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