mineral

Chalcedony

Silicon dioxide (SiO2)

Hardness: 6.5-7 (Mohs), Color: Translucent white to bluish-grey, Luster: Waxy to vitreous, Crystal structure: Trigonal (cryptocrystalline), Cleavage: None, Specific gravity: 2.58-2.64

Hardness: 6

Identified July 10, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs), Color: Translucent white to bluish-grey, Luster: Waxy to vitreous, Crystal structure: Trigonal (cryptocrystalline), Cleavage: None, Specific gravity: 2.58-2.64

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of various rock types, especially volcanic and sedimentary rocks. Common in hydrothermal environments.

Uses & applications

Used primarily for jewelry, lapidary carvings, ornamental stones, and historical use in making tools and seals.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a normal microscope. It was a primary material for making cylinder seals in ancient Mesopotamia.

Field identification & locations

Identify by its waxy luster, conchoidal fracture, and translucency. It is often found in geodes or as botryoidal masses. Common locations include Brazil, USA, Madagascar, and India.