mineral

Chalcedony (Agate)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 6.5 - 7 on Mohs scale. Color: Translucent tan to creamy white. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline). Sheen: Translucent with a conchoidal fracture.

Hardness: 6
Color: Translucent tan to creamy white
Luster: Waxy to vitreous

Identified March 13, 2026More mineral →

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Physical properties

Hardness: 6.5 - 7 on Mohs scale. Color: Translucent tan to creamy white. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline). Sheen: Translucent with a conchoidal fracture.

Formation & geological history

Formed from the deposition of silica-rich groundwater in cavities of volcanic igneous rocks or sedimentary formations. Most common in ancient basaltic lava flows where gas bubbles (vesicles) fill with minerals over millions of years.

Uses & applications

Commonly used for lapidary work, jewelry (cabochons), and historically for tool making (scrapers) due to its toughness and sharp fracture. It is also a popular specimen for rock tumbling.

Geological facts

Chalcedony is technically a fibrous form of silica. It was once believed in ancient times to protect the wearer from 'evil spirits' and was used for cylinder seals in Mesopotamia as far back as 2500 B.C.

Field identification & locations

Identify in the field by its waxy texture, translucency when held to light, and lack of visible crystals. It is commonly found in riverbeds and desert environments such as the American Southwest and Brazil.

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