mineral

Agate (specifically Oco or Banded Agate)

Agate (a variety of Chalcedony), SiO2 (Silicon Dioxide)

Hardness: 6.5–7 on the Mohs scale; Color: Multi-colored (beige, brown, white, grey); Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Multi-colored (beige, brown, white, grey)
Luster: Waxy to vitreous

Identified March 23, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities within volcanic rocks or ancient lavas through the deposition of silica from groundwater. Usually Cretaceous to Tertiary in age, formed over millions of years as layers of silica cool and crystallize.

Uses & applications

Used in gemstone carvings, jewelry (cabochons), interior decoration (coasters/bookends), and industrial burnishing tools because of its hardness.

Geological facts

Agate is known for its concentric banding. The name 'Agate' comes from the Achates River in Sicily, where it was first discovered by ancient Greeks. It is often referred to as the 'Earth Rainbow' because of its varied color patterns.

Field identification & locations

Identify by its waxy luster and translucent to opaque banded patterns. Commonly found in riverbeds, volcanic fields, and the beaches of the Great Lakes (especially the Lake Superior Agate variety). Look for a conchoidal fracture when broken.

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Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

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