sedimentary
Chert / Flint
Chert (Cryptocrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale); Color: brown, tan, gray; Luster: waxy to dull; Crystal structure: hexagonal (cryptocrystalline); Cleavage: none (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- brown, tan, gray
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: brown, tan, gray; Luster: waxy to dull; Crystal structure: hexagonal (cryptocrystalline); Cleavage: none (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments like limestone beds. Common in various geological ages ranging from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modernly used as a road aggregate, in jewelry (when polished), and for lighting fires (due to sparking properties when struck with steel).
Geological facts
Flint is a variety of chert with a darker appearance. Due to its conchoidal fracture, it creates extremely sharp edges even thinner than a steel scalpel.
Field identification & locations
Identify in the field by its waxy texture, smooth conchoidal (shell-like) fractures, and its ability to easily scratch glass. Found often as nodules within limestone or chalk deposits.
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