mineral

Chalcedony (Common Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Grayish-brown, tan, or smoky; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Grayish-brown, tan, or smoky
Luster: Waxy to vitreous

Identified May 13, 2026More mineral →

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Physical properties

Formation & geological history

Forms in volcanic and sedimentary environments when silica-rich groundwater precipitates in cavities (vesicles) or fractures. This specimen likely represents a water-worn nodule formed millions of years ago.

Uses & applications

Commonly used for lapidary work, jewelry (cabochons), carvings, and as a popular specimen for rock hounds and collectors.

Geological facts

Agate is a variety of chalcedony characterized by its microcrystalline structure. It has been used for over 3,000 years for art and jewelry, and was historically believed to protect the wearer from danger.

Field identification & locations

Identify by its waxy luster, translucency when held to light, and smooth, irregular surface. Found globally in riverbeds, beaches, and volcanic soil. Look for the characteristic conchoidal fracture if the stone is chipped.