mineral

Banded Agate (specifically Lake Superior Agate style)

Silicon Dioxide (SiO2) - Chalcedony variety

Hardness: 6.5-7 on Mohs scale; Color: Red, orange, white, and translucent gray; Luster: Vitreous to waxy; Crystal structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.64.

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

Identified April 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed roughly 1.1 billion years ago during the Midcontinent Rift. Volcanic eruptions released basaltic lava with gas bubbles. Silica-rich groundwater later seeped into these vesicles, depositing layers of microcrystalline quartz and iron impurities over time.

Uses & applications

Primarily used for jewelry (lapidary), as a gemstone, or as highly sought-after collector's specimens. Historically used for making burnishing tools or mortars and pestles due to hardness.

Geological facts

Lake Superior Agates are the state gemstone of Minnesota. The distinctive red color is caused by the oxidation of iron within the silica layers. They were dispersed across the Midwest by glaciers during the last Ice Age.

Field identification & locations

Identify by looking for concentric 'fortification' banding and a waxy texture. In the field, look for a translucent edge when held to light or a 'pit' on the surface of an otherwise smooth-looking river rock. Common in gravel pits and along shorelines in the Upper Midwest.

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Mineral/Rock

Banded Gneiss (River Rock/Pebble)

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