mineral

Banded Agate (specifically Lake Superior Agate style)

Agate (Cryptocrystalline Quartz), SiO2

Hardness: 6.5–7 on Mohs scale; Color: Red, orange, white, and translucent; Luster: Vitreous to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 6
Color: Red, orange, white, and translucent
Luster: Vitreous to waxy

Identified March 9, 2026More mineral →

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Physical properties

Hardness: 6.5–7 on Mohs scale; Color: Red, orange, white, and translucent; Luster: Vitreous to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed in gas bubbles (vesicles) within ancient basaltic lava flows. Silica-rich groundwater seeped into these cavities over millions of years, depositing layers of minerals. These specific types are often associated with the Midcontinent Rift System, approximately 1 billion years old.

Uses & applications

Primarily used in jewelry (pendants, beads), lapidary arts, and as highly collectible specimens for rockhounds.

Geological facts

The distinct red and orange coloring in these agates is caused by the oxidation of iron. Agate is the state gemstone of Minnesota and is prized for its high-contrast banding which remains sharp even when tumbled.

Field identification & locations

Identify in the field by looking for 'fortification' banding (concentric lines), a waxy texture when wet, and a translucent quality when held up to the light. Commonly found in glacial till, gravel pits, and along the shores of the Great Lakes.

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