This is the vitreous fulgurite specimen. Dimensions: 4.1 x 1.3 x 0.7″ (10.5 x 3.3 x 1.7cm). Weight — 1.6oz (44 grams). Origin: Russia, Kalmykia.
Some information about fulgurite:
Fulgurites (from the Latin fulgur, meaning «lightning») are natural tubes, clumps, or masses of sintered, vitrified, and/or fused soil, sand, rock, organic debris and other sediments that sometimes form when lightning discharges into ground.
Fulgurites are classified as a variety of the mineraloid lechatelierite. When lightning strikes a grounding substrate, upwards of 100 million volts (100 MV) are rapidly discharged into the ground. This charge propagates into and rapidly vaporizes and melts silica-rich quartzose sand, mixed soil, clay, or other sediments. This results in the formation of hollow, branching assemblages of glassy, tubes, crusts, and vesicular masses. Because of the high temperature differential between the core of a fulgurite and the surrounding soil, many fulgurites show evidence of progressive crystallization: in addition to glasses, many are partially protocrystalline or microcrystalline.
Fulgurites have no fixed composition because their chemical composition is determined by the physical and chemical properties of whatever material is being struck by lightning.