sedimentary
Chalcedony (Chert/Flint variety)
Silicon Dioxide (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: honey-yellow, tan, or grayish; Lustre: waxy to vitreous; Crystal Structure: Cryptocrystalline (hexagonal system); Cleavage: none (conchoidal fracture); Specific Gravity: 2.6–2.64
- Hardness
- 6
- Color
- honey-yellow, tan, or grayish
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: honey-yellow, tan, or grayish; Lustre: waxy to vitreous; Crystal Structure: Cryptocrystalline (hexagonal system); Cleavage: none (conchoidal fracture); Specific Gravity: 2.6–2.64
Formation & geological history
Formed primarily as a sedimentary precipitate from silica-rich fluids in limestone or through the replacement of organic materials. It can also occur in volcanic cavities (geodes).
Uses & applications
Used historically for stone tools and weapons due to its sharp fracture edges. Modern uses include semi-precious jewelry, ornamental lapidary work, and as grinding media in ball mills.
Geological facts
This material was essential to early human civilizations for making arrowheads and spear points. It is essentially a 'microcrystalline' form of quartz where the crystals are too small to see with a standard microscope.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture and waxy surface. Look for it in sedimentary basins or as nodules in limestone. It is harder than steel and will easily scratch glass.
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