Tuesday, March 27, 2012
Fulgurite - The Thunderbolt Stone
The word Fulgurite comes from the Latin word fulgur meaning thunderbolt and are natural hollow glass tubes formed by lightning strikes. They are formed when lightning with a temperature of at least 1,800 °C (3,270 °F) instantaneously melts silica on a conductive surface and fuses grains together; the fulgurite’ tube is the cooled product.
Because it is amorphous, meaning it has no internal crystalline structure, fulgurite is classified as a mineraloid.
The entire process happens over a period of around one second, and leaves evidence of the lightning path and its dispersion over the surface in the form of what looks like a hardened, and usually hollow, plant roots.
Fulgurites can also be produced when a high voltage electrical distribution network breaks and the lines fall onto a conductive surface with sand beneath.
Fulgurites are sometimes referred to as petrified lightning, which is a misnomer as nothing is being replaced or is organic. The glass formed is called lechatelierite and may also be formed by meteorite impacts and volcanic explosions.
Their color varies depending on the composition of the sand they formed in, ranging from black (from basaltic sand) or tan (from quartz sand) to green or a translucent white (from rhyolitic sand) and other varieties are known. Fulgurites can form in solid rock but they are impossible to extract and often look like a round spot of a different color on the host rock.
The interior is normally very smooth or lined with fine bubbles and the exterior is generally coated with rough sand particles and is porous or very textured. They are root-like in appearance and often show branching.