mineral

Raw Agate (Rough Lake Superior Agate or Jasper-Chalcedony Nodule)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

AI-generated identification · may be incorrect

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 July 26, 2026More mineral →

Explore Raw Agate (Rough Lake Superior Agate or Jasper-Chalcedony Nodule) in the encyclopedia →

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Physical properties

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.