gemstone

Lake Superior Agate

Silicon Dioxide (Chalcedony / Quartz), SiO2

Hardness of 7 on the Mohs scale; colors range from red, orange, and brown due to iron oxide staining; waxy to vitreous luster; microcrystalline (cryptocrystalline) crystal structure; no true cleavage, exhibits conchoidal fracture; specific gravity around 2.60 to 2.65.

Identified July 30, 2026More gemstone →

Explore Lake Superior Agate in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed roughly 1.1 billion years ago during the Keweenawan rifting event in the Midcontinent Rift System. Silica-rich hydrothermal solutions filled gas cavities in basaltic lava flows, precipitating concentric layers of chalcedony over time.

Uses & applications

Prized by lapidaries and collectors for cutting, polishing, jewelry making, and display specimens.

Geological facts

Lake Superior agates are the official state gemstone of Minnesota and are famous for their rich red and orange banding, which is caused by the oxidation of iron trapped within the original volcanic host rock.

Field identification & locations

Found primarily in glaciated gravel deposits, riverbeds, and fields throughout the Upper Midwest of the United States (Minnesota, Wisconsin, Michigan, Iowa). Key identifiers include waxy luster, conchoidal fracture, and distinct concentric banding.

Other gemstone specimens

See all

Diamond and Gold Jewelry

Carbon (Diamond) / Au (Gold)

gemstone

Ammolite

Ammolite (Biogenic Aragonite with trace elements; fossils of Placenticeras meeki and Placenticeras intercalare)

mineral

Cubic Zirconia (simulant) or Diamond

ZrO2 (Cubic Zirconia) or C (Diamond)

gemstone

Black Opal Ring (Carved Opal)

Hydrated Silicon Dioxide (SiO2·nH2O)

gemstone

Red Jasper

Silicon Dioxide (SiO2) with Hematite inclusions

sedimentary

Cubic Zirconia (or possibly Diamond)

Zirconium dioxide (or Carbon)

gemstone