mineral

Chalcedony

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs scale; Color: Milky white, bluish-gray, or translucent; Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Milky white, bluish-gray, or translucent
Luster: Waxy to vitreous

Identified July 6, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs scale; Color: Milky white, bluish-gray, or translucent; Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Specific Gravity: 2.58–2.64.

Formation & geological history

Forms in volcanic and sedimentary environments through the deposition of silica from aqueous solutions, often filling cavities (vesicles) in rocks or occurring in veins. It can form at relatively low temperatures.

Uses & applications

Used in jewelry (beads, cabochons), as an ornamental stone, and historically for stone tools due to its conchoidal fracture. It is also a popular collector's specimen.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen under a standard microscope. Common varieties include agate, jasper, and onyx.

Field identification & locations

Identify by its waxy luster, translucency, and lack of visible crystal faces. It is commonly found in basaltic lava flows or as river-worn pebbles in areas with high volcanic activity.