What is a druse?

A druse is a mineral formation consisting of a cavity or void within a rock that is lined with crystals. These crystals, which can be of various minerals, typically grow outward from the walls of the cavity. Druses are often found in geodes or as part of larger mineral deposits and are valued for their aesthetic appeal in the collection of minerals. The term can also refer to a specific type of quartz formation, where small quartz crystals cover a surface.