As about half of you correctly guessed over the weekend, Friday’s mystery object is a fulgurite – lightning-produced glass usually formed when a bolt hits quartz sand, and heats it up to several thousand degrees along the path followed by the current as it earths itself (Jim has a more detailed explanation). Those of you who were thinking it looked like a trace fossil shouldn’t feel too bad, though because I deliberately looked around for an example which looked a bit unusual (although I really should have flipped through a few more results pages on Google, by the looks of it). Here’s a possibly more typical example (source):
And here’s (allegedly) the largest one ever discovered – 17 feet, or almost 6 metres, long – just prior to being excavated (source).
It was found in 1996 at the The International Center for Lightning Research and Testing (ICLRT) at Camp Blanding in Florida, where they actually trigger lightning (by firing rockets up into the clouds) for research purposes. Because of that, they generally know where the bolt hit*.
Sadly, I don’t actually have any fulgurite in my collection, but I saw one or two in situ on the Isle of Arran, the location of the first real field trip I ever went on (as it is for so many UK Geology students). There’s a coastal exposure of a Permian aeolian sandstone where you can find them.
A lot of that particular field trip is a bit of a blur – I mostly remember a sense of being completely overwhelmed, as all the lectures on rock types and structures proved to be completely inadequate preparation for actually recognising and interpreting them in the field. But for some reason, the fulgurite has always stuck in my mind. Visually, this round glassy circle, standing slightly proud from the outcrop, was not particularly impressive. But that something so fleeting and ephemeral as a bolt of lightning could be caught and preserved – a 250 million year-old microsecond, frozen in glass – struck me as pretty darned cool. Even if lightning is my mortal enemy nowadays, it still does.
*I have this memory that I can’t place of seeing a film or TV programme where someone was deliberately creating fulgurites by sticking steel poles into the beach during a lightning storm. Anyone else remember anything like this?
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