mineral

Agate (specifically a Blue Agate Geode Slice)

Chalcedony (cryptocrystalline variety of Quartz); SiO2

Hardness: 6.5–7 on the Mohs scale; Color: Translucent light blue to greyish-white with concentric banding; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.64.

Hardness: 6
Luster: Vitreous to waxy

Identified March 18, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities (vesicles) of volcanic igneous rocks or certain sedimentary rocks. Silicon-rich groundwater seeps into these cavities, depositing layers of silica over millions of years. This specific specimen likely originated in the Tertiary or Cretaceous periods.

Uses & applications

Commonly used in jewelry (cabochons), lapidary art, internal decor (bookends, coasters), and as a popular specimen for mineral collectors. Some industrial use in burnishing tools due to its hardness.

Geological facts

Agates were used by Neolithic people as early as 3,000 BCE for ornaments and amulets. The distinct banding is caused by rhythmic crystallization patterns and periodic changes in the supply of silica or trace impurities like iron or manganese.

Field identification & locations

Identify by its waxy luster on fractured surfaces and the presence of concentric, translucent bands. In the field, look for a rough, cauliflower-like exterior on nodules. Found globally, with major deposits in Brazil, Uruguay, and the United States (Oregon/Washington).

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