mineral

Grey Chalcedony (Tumbled)

Chalcedony (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Translucent grey to smoky blue; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (Microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Translucent grey to smoky blue
Luster: Waxy to vitreous

Identified March 8, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Translucent grey to smoky blue; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (Microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Formation & geological history

Formed from the deposition of silica-rich fluids in cavities, often in volcanic rocks or sedimentary environments. It can form at low temperatures in igneous gas bubbles (amygdules) or via groundwater replacement in wood or bone.

Uses & applications

Commonly used in lapidary arts for cabochons, beads, and architectural accents. Historically used for making seals, cameos, and jewelry.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a standard microscope. Grey chalcedony is often the base material for dyed 'black' or 'blue' agate products found in gift shops.

Field identification & locations

Identify in the field by its waxy luster, conchoidal fracture, and lack of visible grains. It is frequently found in riverbeds or coastal areas near volcanic deposits in locations like Brazil, India, and the United States (Oregon/Washington).