mineral

Chalcedony Nodule (Agate/Chert)

Chalcedony (cryptocrystalline Silicon Dioxide, SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Milky white to tan with internal banding or inclusions; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (microscopic); Cleavage: None, exhibits conchoidal fracture

Hardness: 6
Color: Milky white to tan with internal banding or inclusions
Luster: Waxy to vitreous

Identified March 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in the cavities of volcanic rocks or sedimentary limestone. These nodules can be millions of years old, often surviving the weathering of their original host rock.

Uses & applications

Used primarily for ornamental jewelry (cabochons), stone carvings, and lapidary art. Historically used for making tools like scrapers and arrowheads due to its sharp edges when fractured.

Geological facts

Chalcedony is a cryptocrystalline form of quartz, meaning its crystals are too small to be seen without a microscope. This specific specimen appears to be a small nodule or 'geode fragment' that has weathered out of its matrix.

Field identification & locations

Identify in the field by its waxy texture, translucency when held to light, and characteristic curved (conchoidal) fractures. Common in arid environments and riverbeds near volcanic regions. For collectors, check for internal banding which would classify it as an Agate.

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