mineral

Banded Agate (specifically Red Agate or Sardonyx variety)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

Hardness: 6.5-7 (Mohs scale), Color: Red, brown, and translucent white banding, Luster: Vitreous to waxy, Crystal Structure: Trigonal (microscopic), Cleavage: None (conchoidal fracture), Specific Gravity: 2.58-2.64

Hardness: 6

Identified March 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities (vesicles) of volcanic rocks or ancient lavas. Silica-rich groundwater deposits layers over time, creating the distinct banding seen here. Typical age ranges from millions to hundreds of millions of years (often Tertiary or older).

Uses & applications

Primarily used in jewelry (as pendants, cabochons, and beads), lapidary art, and ornamental carvings. Historically used for making signet rings and cameos due to the distinct color layering.

Geological facts

Ancient Greeks and Romans used these stones as protective amulets. Red agate is often called the 'Warriors' Stone' in folklore. The color in this specimen is likely due to iron oxide impurities (Hematite) within the silica layers.

Field identification & locations

Identify in the field by looking for translucent edges, ultra-fine parallel banding (fortification patterns), and a hardness that can scratch glass. Common locations include Brazil, India, Germany, and the Lake Superior region of the USA.

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