mineral

Chalcedony (Yellow Agate/Chert)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Honey yellow to translucent white; Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Honey yellow to translucent white
Luster: Waxy to vitreous

Identified April 6, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the deposition of silica-rich groundwater in cavities of volcanic rocks or sedimentary formations. This specimen likely formed in a low-temperature hydrothermal environment.

Uses & applications

Used primarily in lapidary arts for gemstones, cabochons, and beads. Historically used for making stone tools (arrowheads/scrapers) due to its sharp conchoidal fracture.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen under a standard microscope. It has been used by humans for over 100,000 years, appearing in early human toolkits.

Field identification & locations

Identify in the field by its waxy luster, smooth conchoidal (shell-like) fractures, and the fact that it cannot be scratched by a steel knife. Often found in gravel beds or weathering out of basaltic lava flows.

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