mineral

Chalcedony Geode Fragment

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Milky white to translucent; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Conchoidal fracture; Specific gravity: 2.58-2.64.

Hardness: 6
Color: Milky white to translucent
Luster: Waxy to vitreous

Identified July 7, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Milky white to translucent; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Conchoidal fracture; Specific gravity: 2.58-2.64.

Formation & geological history

Formed through the deposition of silica-rich groundwater in cavities (vesicles) of volcanic rocks or sedimentary environments. As the water cools or evaporates, silica precipitates, often creating layers or botanical-looking rounded forms.

Uses & applications

Commonly used for lapidary work, jewelry, stone carving, and as decorative collector specimens.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a standard microscope. Many agates and jaspers are actually varieties of chalcedony.

Field identification & locations

Identify by its waxy luster, translucency, and inability to be scratched by a steel knife. Frequently found in riverbeds or weathered volcanic outcroppings in regions like the American West, Brazil, and India.