Agate

Physical Properties

Hardness: 6.5-7 on Mohs scale. Color: Translucent red, orange, and white bands. Luster: Vitreous to waxy. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None. Specific Gravity: 2.58-2.64.

Formation & Geological History

Formed in cavities (vesicles) of volcanic rocks or ancient lava flows where silica-rich groundwater deposited layers of microcrystalline quartz over thousands of years. Often found in basalt vugs.

Uses & Applications

Used extensively in jewelry (cabochons), interior decor (coasters, bookends), precision pendulums, and industrial mortar and pestles due to its hardness and chemical resistance.

Geological Facts

The concentric banding is caused by the periodic precipitation of silica. Many bright pink or neon-colored slices in the market are artificially dyed to enhance the natural banding visibility.

Field Identification & Locations

Identify in the field by its waxy luster, conchoidal fracture, and concentric banding visible when sliced. Common in locations like Brazil, Uruguay, and the Lake Superior region of the US.

Identified on: 5/5/2026

Mode: Standard