mineral

Agate (Polished Nodule)

Agate (Silicon Dioxide, SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Grayish-blue, translucent white; Luster: Vitreous to waxy; Crystal structure: Trigonal (cryptocrystalline); Cleavage: None; Specific gravity: 2.58-2.64

Hardness: 6
Color: Grayish-blue, translucent white
Luster: Vitreous to waxy

Identified April 11, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Grayish-blue, translucent white; Luster: Vitreous to waxy; Crystal structure: Trigonal (cryptocrystalline); Cleavage: None; Specific gravity: 2.58-2.64

Formation & geological history

Formed in cavities (vesicles) of volcanic rocks or ancient hydrothermal veins. Silica-rich fluids deposit layers of chalcedony over time, often beginning from the outer walls inward.

Uses & applications

Used primarily for ornamental purposes, jewelry (pendants, beads), gemstone collecting, and historically for precision instruments like mortars and pestles due to its hardness.

Geological facts

Agate is a variety of chalcedony. This specific specimen appears to be a 'nodule' which has been cut and polished on one face to reveal the inner crystalline structure which can sometimes lead to a hollow geode center.

Field identification & locations

Identify in the field by its waxy luster on broken surfaces and concentric banding. Commonly found in areas with ancient volcanic activity like the Lake Superior region, Brazil, or Germany. Collectors look for unique patterns or 'fortification' banding.

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