This specimen is an example of a mineral that formed in a volcanic environment.
Volcanic: General Collection
Many kinds of minerals can develop in a cooling lava flow, or around volcano crater walls and fissures. Sulfur is perhaps the best-known mineral to form in this way. The mineral crystallizes from some of the gases escaping from the volcano, particularly sulfur dioxide and hydrogen sulfide. Other minerals, such as copper and silver, are also found associated with volcanic activity.
Mount Vesuvius, Italy