Other types of fulgurites are usually vesicular, and may lack an open central tube their exteriors can be porous or smooth. The interior of Type I (sand) fulgurites normally is smooth or lined with fine bubbles, while their exteriors are coated with rough sedimentary particles or small rocks. However, lightning can strike man-made objects, resulting in colored fulgurites. Brightly colored lechatelierites resembling fulgurites are usually synthetic and reflect the incorporation of synthetic materials. Downed high voltage power lines have produced brightly colored lechatelierites, due to the incorporation of copper or other materials from the power lines themselves. Lechatelierite similar to fulgurites can also be produced via controlled (or uncontrolled) arcing of artificial electricity into a medium. Iron is a common impurity that can result in a deep brownish-green coloration. Most natural fulgurites fall on a spectrum from white to black. Material properties (size, color, texture) of fulgurites vary widely, depending on the size of the lightning bolt and composition and moisture content of the surface struck by lightning. Because fulgurites are generally amorphous in structure, fulgurites are classified as mineraloids. Many fulgurites show some evidence of crystallization: in addition to glasses, many are partially protocrystalline or microcrystalline.
The primary SiO 2 phase in common tube fulgurites is lechatelierite, an amorphous silica glass. Description įulgurites are formed when lightning strikes the ground, fusing and vitrifying mineral grains.
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.įulgurites are structurally similar to Lichtenberg figures, which are the branching patterns produced on surfaces of insulators during dielectric breakdown by high-voltage discharges, such as lightning. This results in the formation of generally hollow and/or vesicular, branching assemblages of glassy tubes, crusts, and clumped masses. Such current may propagate into silica-rich quartzose sand, mixed soil, clay, or other sediments, rapidly vaporizing and melting resistant materials within such a common dissipation regime. When ordinary negative polarity cloud-ground lightning discharges into a grounding substrate, greater than 100 million volts (100 MV) of potential difference may be bridged. When composed of silica, fulgurites are classified as a variety of the mineraloid lechatelierite. In a planar view the specimen on the right has a blade-like morphology, but its tubular nature is dramatically shown in a stereo view.įulgurites (from Latin fulgur 'lightning', and -ite), commonly called " fossilized 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. Two small Type I Saharan Desert fulgurites.
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