Mineral

Chalcedony (specifically Agate or Flint)

Silicon Dioxide (SiO₂)

Hardness: 6.5–7 on Mohs scale; Color: Translucent tan to smoky amber; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline (Trigonal/Monoclinic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Translucent tan to smoky amber
Luster: Waxy to vitreous

Identified March 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a chemical precipitate from silica-rich groundwater filling cavities in volcanic or sedimentary rocks. This specific specimen has been water-rolled, likely in a river or beach environment, smoothing its edges over thousands of years.

Uses & applications

Used widely in semi-precious jewelry (beads, cabochons), carvings, and historical tool-making (scrapers, arrowheads) due to its toughness and sharp edges when broken. Also used in industrial mortar and pestles.

Geological facts

Chalcedony is a cryptocrystalline form of quartz. The name comes from the ancient Greek town Chalcedon in Asia Minor. It was one of the first materials used by prehistoric humans to create stone tools because it fractures into extremely sharp edges.

Field identification & locations

Identify in the field by its translucency (light passes through edges), waxy texture, and 'c-shaped' conchoidal fracture scars. Commonly found in gravel pits, riverbeds, and coastal regions globally, especially in Oregon, Brazil, and India.

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