mineral

Agate

Agate (Microcrystalline Quartz, SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Multi-colored banding (white, tan, gray); Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Specific Gravity: 2.58–2.64

Hardness: 6
Color: Multi-colored banding (white, tan, gray)
Luster: Waxy to vitreous

Identified March 23, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily in volcanic rock cavities (vesicles) or sedimentary rocks where silica-rich groundwater deposits layers of chalcedony over time. These specimens can range from thousands to millions of years old depending on the host formation.

Uses & applications

Used widely in jewelry (cabochons, beads), ornamental carvings, industrial abrasive-resistant mortars and pestles, and as highly popular collector specimens.

Geological facts

The banding in agate is caused by the rhythmic crystallization of silica. No two agates are exactly alike, making them a favorite for lapidary artists. Historically, they were used as amulets for protection.

Field identification & locations

Identify in the field by looking for translucent banding, a waxy texture, and a conchoidal (shell-like) fracture. Commonly found in riverbeds, beaches (like the Great Lakes or Pacific Northwest), and volcanic regions. Collectors often use a flashlight to check for translucency.