sedimentary

Agate Nodule / Weathered Agate

Silicon Dioxide (Chalcedony / Quartz, SiO2)

Hardness of 6.5 to 7 on the Mohs scale, colors ranging from gray, brown, white, and translucent blue-gray, waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz structure, conchoidal fracture with no true cleavage, and specific gravity of approximately 2.58 to 2.64.

Identified August 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by the deposition of silica from groundwater or hydrothermal fluids in cavities of ancient volcanic or sedimentary rocks, often developing concentric banding over millions of years.

Uses & applications

Used primarily in lapidary arts, ornamental carvings, making jewelry, and highly prized by rockhounds and mineral collectors.

Geological facts

Agate is a variety of chalcedony that often forms in gas cavities in volcanic rocks, known as amygdales. The concentric bands reflect successive stages of silica deposition.

Field identification & locations

Can be identified in the field by its waxy luster, microcrystalline texture, hardness that scratches glass, and characteristic conchoidal fracture or weathering patterns on the exterior rind. Commonly found in riverbeds, glacial tills, and volcanic regions worldwide.

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Sedimentary limestone with invertebrate fossil imprint

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Sandstone or Siltstone

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Septarian Concretion containing Brachiopods/Crinoids

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Quartz pebble

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Generic Pebble / Rock Fragment

Lithic fragment / Weathered rock

sedimentary

Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

sedimentary