mineral

Agate (Carnelian/Chalcedony)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, translucent grey, and waxy orange; Luster: Waxy to vitreous; Crystal Structure: Trigonal (Microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Hardness: 6
Color: Reddish-brown, translucent grey, and waxy orange
Luster: Waxy to vitreous

Identified May 29, 2026More mineral →

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Physical properties

Formation & geological history

Formed as secondary deposits in volcanic rock cavities (vesicles) where silica-rich groundwater percolates and precipitates layers of microcrystalline quartz over thousands of years. Common in basaltic host rocks.

Uses & applications

Used primarily in lapidary arts for jewelry, cabochons, and decorative carvings. Historically used for making tools, mortar and pestles, and burnishing tools due to its toughness and hardness.

Geological facts

Agate is the official state gemstone of several US states, including Minnesota and Oregon. No two agates are exactly alike due to the unique chemical impurities present during their slow formation process.

Field identification & locations

Identify in the field by its waxy luster, translucent edges when held to light, and characteristic conchoidal fracture. Often found in gravel pits, riverbeds, or areas with ancient volcanic activity. Collectors look for banding and vibrant colors.