5.2" reddish tan melted sand tube fulgurite - Sahara Desert in Boujdour Province, Laayoune-Sakia El Hamra, Morocco
When a lightning bolt strikes the ground in a sandy area, it can deliver over a gigajoule of energy, which is enough to provide power to an all-electric house for a week. Grains of sand are fused in less than a second by the intense heat and energy. Glass is formed at temperatures between 1600º and 2000º Celsius, but the temperature in a bolt of lighting can reach 30,000 kelvins (53,540º Fahrenheit). Amazingly, this is more than five times the temperature on the surface of the sun at 6,000 kelvins (10,340 degrees Fahrenheit). If conditions are right, branching hollow tubes with a sandy outside are formed. The Guinness Book of Records reports that the longest fulgurite known was 17 feet long. The diameter of fulgurite can be as little as one-quarter of an inch, or up to three inches. The thickness of the walls is usually about 2 mm, but can be much thicker depending on how much sand adheres to the glass lining. The exterior of fulgurites is typically coated with porous sand particles which adhered to the molten glass as it cooled. Because glass has a hardness of 5.5, it can withstand wind-blown sand erosion for centuries.
6.5" Twisty hollow sand coated glass tube fulgurite - Sahara Desert in Boujdour Province, Laayoune-Sakia El Hamra, Morocco
Close up of the hollow opening on the previous specimen
Fulgurites come in a variety of colors, depending on what elements are present in the material they are formed from. Colors range from translucent white to tan to gray to green and even black. The tubes are usually relatively smooth on the inside, sometimes with small bubbles. The gas in these bubbles has been analyzed and used to determine the climate of ancient deserts, to investigate paleoecology, and to study the creation of nitric oxide, a fundamental building block of life in ancient geological times. Scientific studies show that fulgurites from the Sahara Desert, where there is almost no lightning activity today, are up to 250 million years old.
1.6" fulgurite with a hollow tube all the way through - Sahara Desert, Grand Erg Occidental, Algeria
Another form of fulgurite is created when an electrical line breaks and the two ends fall on sand so the energy flows from one wire to the other through the sandy soil. Fulgurites may also form when lighting strikes solid rock, forming a coating or crust of glass. These are usually found near the tops of mountains, and are called rock fulgurites, or exogenic fulgurite. Similar rocks include trinitite, which is melted glass formed by the first atomic bomb test in New Mexico, and tektites, which are created by the extreme heat and pressure resulting from the impact of a meteorite.
5.2" Desert reddish tan fulgurite from 300 million year old lightning strike in Sedona, Yavapai County, Arizona
4" fulgurite created by downed power lines that were struck hit by lightning - Northfield, Franklin Co., Massachusetts
8.5" Fulgurite found in the Sahara Desert in Boujdour Province, Laayoune-Sakia El Hamra, Morocco
2.4" Gray and tan fused sand fulgurite - Sahara Desert, Grand Erg Occidental, Algeria
4.5" Lightning fused sand fulgurite - Great Sand Sea, Egypt
1.4" 5.7 gram jade green bubbled trinitite from the 1943 A-Bomb Test at Trinity Site, White Sands, New Mexico
2.3" 20.4g Gem olive green tektite (moldavite) glass formed by the impact of a meteorite - Czech Republic