mineral

Chalcedony (Agate Nodules)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: White, translucent, light grey; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (Microcrystalline); Cleavage: None; Specific gravity: 2.58-2.64

Hardness: 6
Color: White, translucent, light grey
Luster: Waxy to vitreous

Identified April 9, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: White, translucent, light grey; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (Microcrystalline); Cleavage: None; Specific gravity: 2.58-2.64

Formation & geological history

Formed from the deposition of silica from groundwater in cavities of volcanic rocks (amygdules) or sedimentary rocks. This specimen appears to be a weathered nodule likely from the Cenozoic era.

Uses & applications

Used in gemstone carving, jewelry making, lapidary arts, and historically for stone tools due to its conchoidal fracture.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen under a normal microscope. It has been used for seals and amulets since the Bronze Age.

Field identification & locations

Identify by its waxy luster, translucency when held to light, and lack of visible crystal faces. Commonly found in gravel beds, desert washes, and volcanic regions worldwide.