mineral

Banded Agate (Onyx variety)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 6.5 - 7 on Mohs scale; Color: Concentric or parallel bands of grey, white, tan, and brown; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Concentric or parallel bands of grey, white, tan, and brown
Luster: Waxy to vitreous

Identified March 20, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica-rich fluids in volcanic cavities (vesicles) or sedimentary rock veins. The banding represents rhythmic precipitation over thousands of years. Age varies by site, often millions of years old (Cretaceous to Cenozoic).

Uses & applications

Used primarily in lapidary arts for jewelry, beads, and cabochons. Historically used for making mortar and pestles due to its hardness and resistance to chemicals. Highly collected as tumbled stones or 'worry stones'.

Geological facts

The parallel banding seen in this specimen is often specifically referred to as 'onyx' when the bands are straight rather than curved. Agate was a highly valued gemstone in ancient times and was used as amulets to protect against fever.

Field identification & locations

Identify by its translucency (light passes through the edges), smooth waxy feel, and distinct layering. Common in basaltic areas and river beds in Brazil, India, and the United States (Lake Superior/Oregon). To collect, look for stones that appear glass-like when wet with visible internal layers.

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