Banded Agate

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Red, brown, and cream bands; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64.

Formation & Geological History

Formed in cavities within volcanic or metamorphic rocks where silica-rich groundwater deposits layers of chalcedony over time. These layers often follow the contours of the cavity, creating distinct banding patterns.

Uses & Applications

Used extensively in jewelry (cabochons, beads), decorative carvings, paperweights, and as 'worry stones'. Also used in precision instruments like mortar and pestles due to hardness.

Geological Facts

The name 'Agate' comes from the Achates River in Sicily where the stones were first discovered. Agates are known for their distinct concentric banding which is actually a record of the changing mineral chemistry in the groundwater during formation.

Field Identification & Locations

Identify by looking for waxy luster on fractured surfaces and rhythmic color banding. Commonly found in riverbeds and on beaches in volcanic regions like Brazil, India, and the Lake Superior region of the USA.

Identified on: 4/29/2026

Mode: Standard