mineral

Agate

Chalcedony (SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Tan, grey, white, translucent. Luster: Waxy to vitreous. Crystal structure: Hexagonal (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Tan, grey, white, translucent
Luster: Waxy to vitreous

Identified June 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities of volcanic rocks or ancient lavas. Silica-rich groundwater percolates into vesicles, precipitating layers of microcrystalline quartz over thousands of years. Often dating back to the Proterozoic or Mesozoic eras.

Uses & applications

Used extensively in jewelry (cabochons), lapidary arts, ornaments, and precision industrial bearings or mortars and pestles due to its hardness and resistance to acids.

Geological facts

Agates are often banded, but 'nodular' or 'rough' agates like this one show the characteristic waxy texture and botryoidal internal structures before being cut. The ancient Greeks named it after the Achates River in Sicily.

Field identification & locations

Found in gravel beds, lake shores (like Lake Superior), and volcanic outcrops globally. Identify in the field by its waxy luster, translucency when held to light, and conchoidal (shell-like) fracture surfaces.