Rock Identifier
Chalcedony (Agate/Carnelian precursor) (Chalcedony (Silicon Dioxide, SiO2)) — mineral
mineral

Chalcedony (Agate/Carnelian precursor)

Chalcedony (Silicon Dioxide, SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Translucent white to pale orange/yellow; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (hexagonal system); Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.64.

Hardness
6
Color
Translucent white to pale orange/yellow
Luster
Waxy to vitreous
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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Translucent white to pale orange/yellow; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (hexagonal system); Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.64.

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of igneous and sedimentary rocks. This specimen likely weathered out of a volcanic host rock. It can form in various geological ages from the Precambrian to Holocene.

Uses & applications

Commonly used in lapidary work for cabochons, beads, and carvings. Historically used for making stone tools (scrapers/arrowheads) due to its conchoidal fracture. Also used as an abrasive or in precision bearings.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen under a normal microscope. When it has concentric banding, it is called Agate; when it is reddish-orange, it is Carnelian.

Field identification & locations

Identify in the field by its waxy appearance, translucency when held to light, and ability to scratch glass. Found globally in riverbeds, beaches, and volcanic regions. Collectors look for pieces with high clarity or internal patterns.

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