sedimentary

Chalcedony on Ironstone

Silicon Dioxide (SiO2) with Iron Oxide (Fe2O3/FeOOH)

AI-generated identification · may be incorrect

Hardness: 6.5-7. Color: Yellowish-orange, brown, and greyish-blue. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Opaque matrix with translucent mineral crusts.

Hardness: 6
Color: Yellowish-orange, brown, and greyish-blue
Luster: Waxy to vitreous

Identified July 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica from groundwater within cavities or fractures of iron-rich sedimentary rocks or volcanic host rocks. The iron minerals are likely hematite or goethite, representing an oxidative environment.

Uses & applications

Collected as mineral specimens. The ironstone matrix can be used as low-grade iron ore, while the chalcedony (agate/jasper) components are often used in jewelry or as lapidary material.

Geological facts

This specimen displays a classic vuggy texture where silica-rich fluids have partially filled a void in the host ironstone. Chalcedony often forms in botryoidal (grape-like) or druzy habits in these environments.

Field identification & locations

Identify by the high hardness of the colorless/grey sections (cannot be scratched by steel) and the characteristic rusty, earthy appearance of the iron-bearing matrix. Common in arid desert regions and weathered volcanic terrains.