sedimentary
Flint / Chert
Silicon dioxide (Microcrystalline Quartz, SiO2)
Hardness: 7 on the Mohs scale. Color: Tan, brown, gray, or white with a weathered cortex. Luster: Waxy to vitreous. Crystal structure: Microcrystalline / cryptocrystalline quartz (chalcedony). Cleavage: None, exhibits characteristic conchoidal fracture. Specific gravity: 2.60 to 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Tan, brown, gray, or white with a weathered cortex
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on the Mohs scale. Color: Tan, brown, gray, or white with a weathered cortex. Luster: Waxy to vitreous. Crystal structure: Microcrystalline / cryptocrystalline quartz (chalcedony). Cleavage: None, exhibits characteristic conchoidal fracture. Specific gravity: 2.60 to 2.65.
Formation & geological history
Formed in marine environments as a chemical sedimentary rock, typically through the replacement of calcium carbonate in limestone or chalk by silica-rich solutions, or through the accumulation of siliceous skeletal remains of marine organisms like diatoms and radiolarians.
Uses & applications
Historically used extensively for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Also used historically with steel to create sparks for fire-starting, and in construction as road aggregate.
Geological facts
Flint and chert are chemically identical, though 'flint' traditionally refers to varieties found in chalk or marly limestone formations, while 'chert' is found in limestones. It has been utilized by humans for toolmaking for over two million years.
Field identification & locations
Can be identified in the field by its smooth, waxy luster, conchoidal fracture patterns showing sharp edges, and hardness capable of scratching glass. Commonly found nodular within chalk or limestone formations worldwide.
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