mineral

Chalcedony (Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Waxy white, grey, or pale orange; Luster: Vitreous to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None; SG: 2.6-2.64

Hardness: 6
Color: Waxy white, grey, or pale orange
Luster: Vitreous to waxy

Identified April 6, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Waxy white, grey, or pale orange; Luster: Vitreous to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None; SG: 2.6-2.64

Formation & geological history

Formed from the deposition of silica-rich groundwater in cavities of igneous and sedimentary rocks. Common in volcanic vesicles and as replacement material in fossils.

Uses & applications

Used primarily in lapidary arts for beads, cabochons, and jewelry. Historically used for making flint tools and seal stones.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen under a standard microscope. Translucent varieties are often called 'Carnelian' (if orange) or simply common Agate.

Field identification & locations

Identify by its waxy luster, conchoidal (shell-like) fracture, and inability to be scratched by a steel knife. Commonly found in riverbeds and volcanic regions.