mineral

Lake Superior Agate

Silicon Dioxide (SiO2) with impurities

AI-generated identification · may be incorrect

Hardness: 7; Color: Banded red, orange, and white (iron stains); Luster: Vitreous to waxy; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6.

Hardness: 7
Color: Banded red, orange, and white (iron stains)
Luster: Vitreous to waxy

Identified June 30, 2026More mineral →

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Physical properties

Hardness: 7; Color: Banded red, orange, and white (iron stains); Luster: Vitreous to waxy; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6.

Formation & geological history

Formed roughly 1.1 billion years ago during the Midcontinent Rift. Gas bubbles in basaltic lava filled with mineral-rich groundwater, precipitating quartz layers in cavities.

Uses & applications

Primarily used for jewelry, lapidary art, and collection. Highly prized by rockhounds for its distinct banding and historical significance.

Geological facts

Designated as the official state gem of Minnesota in 1969. Every agate's pattern is unique, formed by the slow cooling and deposition of silica.

Field identification & locations

Identify by looking for waxy luster, pit marks/cortex (peeled appearance), and translucent concentric bands when held to light. Common on shores of Lake Superior and in glacial drift throughout the upper Midwest USA.