mineral

Polished plume agate slice

Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent to opaque, white-gray chalcedony with brown-orange plume-like iron staining; vitreous to waxy luster, cryptocrystalline structure, no cleavage, specific gravity about 2.6. The specimen is cut and highly polished.

Identified September 15, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater filled cavities in volcanic lava, later crystallizing as chalcedony and forming plume patterns from iron oxides. Most agates formed during the Cenozoic to Mesozoic eras, depending on locality.

Uses & applications

Used for cabochons, jewelry, bookends, display slices, and ornamental objects; valued mainly for attractive pattern, translucency, polish, and size.

Geological facts

Agate is a variety of chalcedony, and its internal banding or plume structures often reveal changing chemistry during cavity filling. Brown coloration commonly comes from hematite or goethite.

Field identification & locations

Identify by its waxy translucency, very fine quartz texture, conchoidal fracture, and resistance to scratching by steel; it commonly occurs in volcanic regions of Brazil, Uruguay, Mexico, the United States, and Madagascar.