mineral

Agate (Polished Slice)

Banded Chalcedony (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Purple, white, and brown (this specimen appears dyed purple); Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Purple, white, and brown (this specimen appears dyed purple)
Luster: Waxy to vitreous

Identified April 10, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities of volcanic rocks or ancient lavas, where silica-rich groundwater deposited layers of chalcedony over millions of years. This specimen shows a 'geode' or 'nodule' cross-section.

Uses & applications

Used primarily for ornamental purposes, jewelry (pendants, cameos), coasters, bookends, and collection displays. Also used in precision scales and mortars due to its hardness.

Geological facts

Agates are often artificially dyed to enhance their natural banding, which is likely the case for the vibrant purple hues in this slice. Real agate banding is extremely fine and can contain thousands of layers per inch.

Field identification & locations

Identify in the field by its waxy luster on broken surfaces, translucency when held to light, and concentric banding. Commonly found in Brazil, Uruguay, and the Lake Superior region of the USA.