mineral

Chalcedony (Agate/Quartz)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: translucent white to brownish-grey; Luster: waxy to vitreous; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6

Hardness: 6
Color: translucent white to brownish-grey
Luster: waxy to vitreous

Identified May 13, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: translucent white to brownish-grey; Luster: waxy to vitreous; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed from the deposition of silica from groundwater in cavities of igneous rocks, particularly volcanic lavas, or in sedimentary environments. Common in Cenozoic deposits.

Uses & applications

Commonly used for lapidary work, jewelry (beads and cabochons), ornamental carvings, and as a collector's specimen.

Geological facts

The specimen on the right appears to be a polished 'nodule' or river-rock chalcedony, while the one on the left shows a natural sugary crystalline surface typical of a geode fragment.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy luster on broken surfaces, and lack of visible crystal grains. Often found in riverbeds or volcanic ash beds.