Agate (specifically Lake Superior Agate style or Banded Chalcedony)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Multi-colored bands of white, orange, and red; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.58-2.64

Formation & Geological History

Formed as secondary deposits in cavities (vesicles) of basaltic or volcanic rocks. Silica-rich groundwater permeates these pockets, depositing layers of chalcedony over millions of years. This piece specifically shows orbital or concentric banding characteristic of high-quality agates.

Uses & Applications

Used primarily in lapidary arts for jewelry, gemstones, and carvings. Also used historically for precision mechanical parts like scale bearings and mortars/pestles due to its high hardness and chemical resistance.

Geological Facts

Agate was named by the Greek philosopher Theophrastus, who discovered the stone along the shore line of the river Achates in present-day Sicily. It was one of the first materials used by humans for hardstone carving and seals.

Field Identification & Locations

Identify in the field by looking for translucent edges, concentric banding, and a waxy texture. Commonly found in riverbeds, lake shores (especially Lake Superior), and volcanic gravel pits worldwide.

Identified on: 5/20/2026

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