mineral

Chalcedony (Agate/Jasper mix in host rock)

Chalcedony (cryptocrystalline Silicon Dioxide, SiO2)

Hardness: 6.5–7 (Mohs scale); Color: Blue-grey translucent centers with reddish-brown opaque (iron-stained) outer edges; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (microscopic); Cleavage: None (conchoidal fracture).

Hardness: 6
Luster: Waxy to vitreous

Identified February 15, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of igneous rocks or sedimentary layers. This specifically appears to be a small nodule or seam filling likely from a volcanic environment, formed when silica-rich fluids cooled and crystallized over thousands of years.

Uses & applications

Used primarily for semi-precious jewelry (lapidary), decorative carvings, and as collectible mineral specimens. Industrially used for mortar and pestles due to its hardness and resistance to chemicals.

Geological facts

Chalcedony was highly prized in the ancient world; it was used for making seals in Bronze Age Crete. The blue-grey hue is often caused by the Tyndall effect, where light scatters off microscopic particles within the stone.

Field identification & locations

Identify in the field by its waxy luster, conchoidal (shell-like) fracture, and inability to be scratched by a steel knife. It is frequently found in basaltic lava flows or in desert regions as 'float' rocks. Common locations include Oregon and Arizona in the USA, Brazil, and India.

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