mineral

Chalcedony Pebble with Jasper/Iron Oxide Cortex

Silicon Dioxide (SiO2)

Hardness 6.5-7 on Mohs scale; color ranges from tan, reddish-brown, and translucent grayish-chalcedony center; waxy to vitreous luster; microcrystalline/cryptocrystalline structure; no cleavage; specific gravity ~2.6

Identified July 26, 2026More mineral →

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Physical properties

Formation & geological history

Formed via low-temperature precipitation of silica-rich fluids within cavities, gas bubbles, or fractures of volcanic or sedimentary rocks. Over time, weathering rounds the nodules into water-worn pebbles.

Uses & applications

Commonly used as lapidary material, for tumbling, wire-wrapping, cabochon cutting, or as a decorative specimen for rockhounding enthusiasts.

Geological facts

Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. When combined with iron oxides, it produces reddish-brown jasper coatings around translucent agate or chalcedony cores.

Field identification & locations

Identified by its rounded water-worn shape, waxy luster, hardness (scratches glass), and translucent silica center exposed through a worn iron-rich rind or cortex. Commonly found in gravel bars, riverbeds, and beach deposits in volcanic terrains worldwide.

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