sand fulgurite

A sand fulgurite is a glassy silica mineral formed when lightning strikes sand. These are typically tubular, branching structures, often less than 3 meters long but sometimes reaching up to 20 meters. The interior of a sand fulgurite is usually lined with glass, and sand grains from the surrounding area adhere to its exterior. They are commonly found on sandy shores, such as those of Lake Michigan and the Atlantic coast. Another variety, rock fulgurites, appear as thin, glassy crusts on rocks, often found on mountain summits. The term "fulgurite" comes from the Latin word for lightning.12