mineral

Agate (specifically Waterline or Onyx-type Agate)

Silicon Dioxide (SiO2) - variety Chalcedony

Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, gray, and translucent tones; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Brown, tan, gray, and translucent tones
Luster: Waxy to vitreous

Identified May 7, 2026More mineral →

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Physical properties

Formation & geological history

Formed in volcanic rock cavities (vesicles) or sedimentary fissures. As silica-rich groundwater seeps into these cavities, layers of chalcedony precipitate. Parallel horizontal bands, known as waterline agate, suggest gravity-fed deposition during slow cooling or evaporation.

Uses & applications

Primarily used for lapidary work, jewelry making (cabochons), interior decoration, and as a popular specimen for mineral collectors.

Geological facts

The parallel, flat bands in this specimen indicate it was oriented a specific way when the silica settled, acting as a geological level or 'paleo-horizontal' indicator.

Field identification & locations

Identify in the field by its waxy luster on fractured surfaces and its superior hardness (it will scratch glass). Commonly found in areas with ancient volcanic activity like the Lake Superior region or Brazil.

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