mineral
Lake Superior Agate
Silicon Dioxide (SiO2) with impurities
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
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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.
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Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Schist
Schist
Metamorphic
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock
Banded Gneiss (River Rock/Pebble)
Gneiss (specifically a banded variety often found as a river rock)
Metamorphic Rock