drusy

Drusy is a geological term used to describe a coating or crust of tiny crystals covering a rock surface, nodule, or hollow cavity. The resulting texture is glittering and can resemble a fine frost or a crust of sparkling sand. Drusy surfaces are most commonly formed by the precipitation of mineral-rich fluids in voids, on fractures, or over the surfaces of growing crystals after the main crystal framework has formed.

Commonly affected minerals include quartz and calcite, though other minerals such as chalcedony, garnet, or goethite can also form drusy coverings. The crystals are typically well-formed but very small, densely packed, and oriented in various directions, which maximizes light reflection and contributes to their sparkling appearance. Colors vary with the minerals present and impurities; drusy quartz can be colorless or tinted, and amethyst or citrine varieties may appear when incorporated.

The term drusy derives from the French druse or druse, meaning a crust of small crystals. In jewelry and decorative contexts, drusy textures may occur naturally or be enhanced by mounting a natural druse or by applying a thin layer of crystals to create a glittering surface.

Uses and care: Drusy specimens are valued by mineral collectors and used in jewelry and ornamentation. Because the surface consists of many delicate microcrystals, drusy pieces can be fragile. Cleaning is best done with a soft brush and mild water, avoiding harsh chemicals that could dissolve the surface.