Avug, vugh, or vugg (/vʌɡ/)[1] is a small- to medium-sized[quantify] cavity inside rock. It may be formed through a variety of processes. Most commonly, cracks and fissures opened by tectonic activity (folding and faulting) are partially filled by quartz, calcite, and other secondary minerals. Open spaces within breccias formed by an ancient collapse are another important source of vugs.[citation needed]
Vugs may also form when mineral crystalsorfossils inside a rock matrix are later removed through erosionordissolution processes, leaving behind irregular voids. The inner surfaces of such vugs are often coated with a crystal druse. Fine crystals are often found in vugs where the open space allows the free development of external crystal form.
I don't know about you people but I would do anything for a crystal or gemstone