What is Fulgurite and Types of Fulgurite

Fulgurite is a naturally occurring glassy formation created when lightning strikes a surface, such as sand, soil, rock, or other minerals. The intense heat from the lightning, which can exceed 30,000°C (54,000°F), melts the material upon impact. This molten material quickly cools and solidifies into a tubular, glass-like structure, often preserving the shape of the lightning's path. Fulgurites are sometimes referred to as "fossilized lightning."

What is Fulgurite

Fulgurite is a type of natural glass formed when lightning strikes sand or rocky soil, instantly melting the silica or other minerals present, which then cools rapidly to create a hollow, glass-lined tube or an irregular glassy structure that traces the path of the lightning through the ground.

Fulgurites resemble roots with rough surface. However, the inner surface is smooth and glassy, because of the fact that the sand cools rapidly and solidifies. Their size is based on the strength of the lightning and the thickness of the sand bed.

Lightning is more frequent during certain times of the year, so fulgurite formation also follows this pattern. They are more likely to form during the summer months when thunderstorms are more prevalent.

Fulgurites are natural glass tubes formed when lightning strikes sand. Photos: Fulgurite Lightning Portugal

Although most of those found are only a few inches in length, some have been found which are thirty feet or more in length. Small pebbles in the sand frequently cling to the fulgurites. Some fulgurites are no larger in diameter than a soda straw, and others have the diameter of a good sized carrot.

Fulgurites are fragile and should be dug out with extreme care and patience. When one is found there may be others near it, or it may be the only one present. The objective of the trip might be gemstone pebbles, or microfossils, or small crystals, or colored sand for sand bottles, but the possibility of fulgurites should be in the consciousness of the collector. 

The technical name for naturally fused sand is lechatelierite. The fulgurite will be mainly silica. It will have the same exterior color as the surrounding sands, but perhaps a little darker in appearance because of the dark fused glass interior. Sand colors vary from beige to buff to gray, charcoal, or drab muted tints of pink, yellow or green. These other colors are due to the presence of other minerals than quartz in the sand. Some of these minerals may be feldspar, hornblende, biotite, and clay and iron minerals.

The fulgurites are known since 1711 and they are appreciated for their scientific value. A fulgurite that is 250 million years old found in the Sahara, has confirmed that the desert was a fertile area where the storms were frequent.

The favorite places to look for the deposits of this mineraloid are the deserts, coastal dunes, on lake shores, sea shores, sandy hills where lightning often strikes, sandy cliffs by rivers, on islands, and in sandy fields. Fulgurites have been reported in the following states, but the list is probably only a beginning: Florida, Georgia, North Carolina, South Carolina, Texas, Illinois, Wisconsin, Indiana, Michigan, Ohio, Maine, Massachusetts, New Jersey, Nebraska, South Dakota, Colorado, Oregon, Arizona, and California.

Characteristics

Composition: Fulgurites are primarily composed of silica (SiO₂), especially when formed in quartz-rich sands. They may also contain impurities, such as metals, minerals, or organic material, depending on the composition of the surface struck by lightning.

Colors range from gray, brown, black, green, or even translucent, depending on the mineral content of the surrounding material. Fulgurites formed in iron-rich sand or soil may appear darker, while those from pure quartz sand are more translucent or light-colored.

Shape: The shape can be tubular, branching, or irregular, resembling roots or coral structures, reflecting the path the lightning took through the ground.

Hollow, Tubular Shape: Fulgurites typically have a hollow core, formed by the lightning's rapid vaporization of material during the strike. The outer surface is rough and irregular, while the inner surface is often smooth or glassy.

Branching Patterns: Some fulgurites exhibit a branching structure that resembles tree roots. This occurs when the lightning forks underground or spreads across a surface.

Size Variability: Fulgurites can vary greatly in size, from a few centimeters to several meters long, depending on the strength of the lightning and the type of material struck.

Fragility: Fulgurites are generally fragile and can break easily. This fragility makes them difficult to extract without damage.

Fulgurites specimens from Morocco

Formation of Fulgurites

Fulgurites are formed when a lightning bolt strikes the ground and melts the sand, soil, or rock. The intense heat of the lightning bolt can reach temperatures of up to 50,000 degrees Fahrenheit, which is hot enough to melt any material on Earth.

The lightning bolt also creates a shock wave that travels through the ground and shatters the surrounding rocks and minerals. The molten sand, soil, and rock then flow into the cracks and fractures created by the shock wave.

As the molten material cools, it forms a glass tube or branching structure. The shape of the fulgurite is determined by the path of the lightning bolt as it traveled through the ground.

Types of Fulgurites

There are five main types of fulgurites, classified based on the material the lightning strikes:

Sand Fulgurites: These are the most common type of fulgurite, typically found in deserts or beaches with loose, dry sand. They resemble hollow, branching tubes with a glassy interior and a rough, melted-sand exterior. Their size and shape depend on the intensity of the lightning strike and the depth of the sand.

Soil Fulgurites: These fulgurites form in various soil types, including clay-rich, silt-rich, or loess. They can have a wider range of shapes than sand fulgurites, appearing as tubes, branches, blobs, or irregular masses. They may also produce exogenic fulgurites, also known as droplet fulgurites, which are small glass beads ejected during the lightning strike.

Caliche Fulgurites: These uncommon fulgurites form in caliche-rich soil, a type of soil with a high calcium carbonate content. They are characterized by thick walls with a lower glass content compared to other fulgurites.

Rock Fulgurites: Formed when lightning strikes rocks, these fulgurites appear as glassy veins or branching channels along the rock surface or lining cracks within the rock. They are more massive and harder than other fulgurites and are commonly found on mountaintops, which are natural lightning rods.

Exogenous fulgurites: they can be spherical or drop-shaped.

Exogenic Fulgurites. Photo: WorthPoint Corporation