mineral

Lake Superior Agate

Banded Chalcedony / Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Red, orange, white, tan, and gray bands; Luster: Waxy to vitreous; Crystal Structure: Trigonal/Microcrystalline; Cleavage: None, conchoidal fracture; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Red, orange, white, tan, and gray bands
Luster: Waxy to vitreous

Identified July 23, 2026More mineral →

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Physical properties

Formation & geological history

Formed during the Mesoproterozoic era about 1.1 billion years ago in the North American Midcontinent Rift System. Silica-rich fluids deposited layers of microcrystalline quartz within gas cavities (vesicles) of volcanic basalt lava flows.

Uses & applications

Popular as a lapidary gemstone, used for jewelry, cabs, carvings, and highly sought after by rock collectors.

Geological facts

The Lake Superior Agate is the official state gemstone of Minnesota, designated in 1969. It is characterized by rich iron-stained color variations and fine, distinct fortification banding.

Field identification & locations

Identified by intricate fortification banding, waxy texture, and iron oxide color accents. Found around Lake Superior, particularly along beaches and gravel pits in Minnesota, Wisconsin, Michigan, and Iowa.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Sandstone with Mineral Veining or Crust

Sedimentary Sandstone (mostly SiO2 with Fe2O3 tinting)

sedimentary

Potassium Feldspar (Orthoclase)

Orthoclase (KAlSi3O8)

mineral

Gypsum (variety Selenite or Alabaster)

Calcium sulfate dihydrate (CaSO4·2H2O)

Mineral

Nephrite Jade

Nephrite

Mineral/Rock