Fulgurite: What is Fulgurite and Types of Fulgurite

What is Fulgurite?

Fulgurites are natural hollow glass tubes often formed during lightning strikes, in quartzose sand, silica, or soil. Sometimes they are referred to as petrified lightning. This process occurs over a timespan of around one second. The lightning bolt traveled through a thick layer of dry sand, and it heated to a temperature greater than 18000 C  (32000 F). 

Fulgurites are usually occurring beneath the surface of the sand and their shape reflects the way that makes lightning as it dispersed into 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.

Fulgurite: a Petrifying Flash of Lightning!
Fulgurite: a Petrifying Flash of Lightning. Photo: Fulgurite Lightning Portugal/Facebook

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 

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 Fulgurite

According to the composition and morphology, fulgurite can be classified into several types:

  • Sand fulgurite: It is the one that is generated when the lightning strike falls on soils that have a sandy texture.

  • Clay Fulgurite: it is usually formed when the lightning strike occurs in soils with abundant amounts of clay and generates another type of structure in this mineraloid.

  • Calcium sediment: It is another variety that has a large amount of calcium in the form of precipitated sediments.

  • Rock fulgurite: it usually forms on other rocks and one in both structures. They are usually somewhat larger in size and have a higher hardness.

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

Fulgurite: a Petrifying Flash of Lightning!. Exogenic Fulgurites
Exogenic Fulgurites. Photo: WorthPoint Corporation

Exogenic Fulgurites

Exogenic fulgurites feature an amorphous and often bubbly appearance due to the rapid manner in which the airborne, liquefied materials cool down. They are generally dark green in colour (as a result of a moderate iron oxide content), differing from traditional fulgurites, which are typically carrot, brown or tan.

See also:
Rainbow Obsidian
Rare Blue Skarn

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