mineral
Raw Agate (Rough Lake Superior Agate or Jasper-Chalcedony Nodule)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5-7 on Mohs scale; Color: reddish-orange, tan, yellow, brownish-pink; Luster: waxy to dull in unpolished form, vitreous when broken; Crystal Structure: Trigonal (microcrystalline); Cleavage: none, conchoidal fracture; Specific Gravity: ~2.58-2.64
- Hardness
- 6
- Color
- reddish-orange, tan, yellow, brownish-pink
- Luster
- waxy to dull in unpolished form, vitreous when broken
Identified More mineral →
Explore Raw Agate (Rough Lake Superior Agate or Jasper-Chalcedony Nodule) in the encyclopedia →Identify your own rocks.
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: reddish-orange, tan, yellow, brownish-pink; Luster: waxy to dull in unpolished form, vitreous when broken; Crystal Structure: Trigonal (microcrystalline); Cleavage: none, conchoidal fracture; Specific Gravity: ~2.58-2.64
Formation & geological history
Formed in cavities within ancient basaltic lava flows where silica-rich groundwater deposited successive layers of chalcedony quartz over hundreds of millions of years (Mesoproterozoic Era, ~1.1 billion years ago).
Uses & applications
Lapidary material for tumbling, polishing, slabbing, making cabochons, wire-wrapping, and general rock collecting.
Geological facts
Lake Superior Agates are Minnesota's official state gemstone, known for their distinct iron-rich red, orange, and white banding patterns created by oxidation during formation. Uncut specimens often show a rough, pitted exterior husk called 'peeling' or 'pitted skin'.
Field identification & locations
Identified in the field by its translucent properties when back-lit, waxy texture, high hardness (scratches steel), and characteristic pitted or husky exterior. Commonly found along gravel pits, riverbeds, and shores around Lake Superior and glacial till deposits across the US Midwest.
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