mineral

Chalcedony

Chalcedony (SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Translucent grey to brownish-white. Luster: Waxy to vitreous. Crystal Structure: Trigonal (cryptocrystalline). Cleavage: None. Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Translucent grey to brownish-white
Luster: Waxy to vitreous

Identified April 8, 2026More mineral →

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Physical properties

Hardness: 6.5–7 on Mohs scale. Color: Translucent grey to brownish-white. Luster: Waxy to vitreous. Crystal Structure: Trigonal (cryptocrystalline). Cleavage: None. Specific Gravity: 2.58–2.64.

Formation & geological history

Formed from the deposition of silica-rich water at relatively low temperatures in cavities of other rocks, typically volcanic. It is a cryptocrystalline variety of silica.

Uses & applications

Used primarily as semi-precious gemstones, in lapidary work for carvings or jewelry, and historically for sharp tools and arrowheads.

Geological facts

Chalcedony was highly prized in the ancient world; it was used for the cylinder seals of Babylon. It derives its name from the ancient Greek town of Chalkedon.

Field identification & locations

Identify in the field by its waxy luster, conchoidal fracture (smooth, curved breaks), and hardness (it will scratch glass). Common in dry, volcanic regions like the American Southwest.