mineral

Agate (specifically Carnelian Agate or Lake Superior style Agate)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

Hardness: 6.5–7 on Mohs scale; Color: Red, orange, brown with translucent bands; Luster: Waxy to vitreous; Crystal Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64

Hardness: 6
Color: Red, orange, brown with translucent bands
Luster: Waxy to vitreous

Identified April 10, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities (vesicles) of volcanic rocks or sedimentary formations where silica-rich groundwater precipitates in layers over millions of years. This specimen likely dates back to the Mesoproterozoic era (approx. 1.1 billion years ago) if it is a Lake Superior variety.

Uses & applications

Used primarily in jewelry (cabochons, beads), decorative lapidary arts, and as high-quality collector specimens. Historically used for making precision bearings and mortars/pestles due to its hardness.

Geological facts

Agate is the state rock of Minnesota. The concentric bands are caused by rhythmic crystallization or variations in the impurities (like iron oxide) present during the cooling and deposition of silica.

Field identification & locations

Identify in the field by looking for 'peeling' layers, waxy texture, and light translucency when held to a light source. Often found in glacial till, riverbeds, or rocky shorelines in the Great Lakes region or the Pacific Northwest.

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