vuggy

Vuggy is a geological descriptor applied to rocks that contain numerous voids or cavities known as vugs. The spaces may be empty or lined with mineral crystals, producing a jagged, glittering interior when viewed in hand specimen. The term is used in mineralogy, petrology, and ore-deposit descriptions.

Vug formation occurs by dissolution of soluble minerals, as in karst processes in limestones and dolostones, or by tectonic widening of fractures. Later mineral-rich fluids precipitate crystals within the cavities, often creating drusy textures with calcite, quartz, or dolomite.

Vuggy textures are common in carbonate rocks and in some volcanic and hydrothermal rocks where secondary minerals fill cavities. They can increase porosity and permeability, influencing fluid flow in aquifers and oil-and-gas reservoirs. Well-formed crystals in vugs are also valued by collectors.

In field descriptions, a vuggy character can indicate diagenetic or hydrothermal alteration history and may guide exploration for mineralization.