Mineral

Agate (Slab)

Agate (Cryptocrystalline variety of Quartz, SiO2)

Hardness: 6.5-7 on the Mohs scale; Color: Multi-colored bands, often translucent grey or brown as seen here; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline chalcedony); Cleavage: None; Specific Gravity: 2.58–2.64.

Hardness: 6
Luster: Waxy to vitreous

Identified March 22, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily in volcanic and metamorphic rocks. It develops in cavities (vesicles) within ancient lava flows as silica-rich groundwater deposits layers of chalcedony over thousands of years. They are commonly found in formations ranging from 10 million to over 1 billion years old.

Uses & applications

Commonly used in jewelry (cabochons), interior decor (coasters, bookends, or lighting), industrial mortars/pestles, and as metaphysical or healing stones in the collector market.

Geological facts

Agate is named after the Achates River in Sicily where it was first discovered. While it looks like one solid piece, the bands are actually microscopic crystals of quartz and moganite growing in alternating rhythmic patterns.

Field identification & locations

Identify by its translucent nature when held to light and its waxy luster. In the field, look for rounded nodules with a rough, 'brain-like' or pitted exterior. Common locations include Brazil, Uruguay, Lake Superior (USA), and India.

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