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 Post subject: Fossil lightning.
PostPosted: Sun Aug 17, 2014 7:26 am 
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Joined: Sat Jul 14, 2012 5:11 pm
Posts: 657
Not quite a gem, but very interesting.
Fraser Island, on the Queensland coast, is made of pure silica.
It has desert-like sand-dunes, rising up to 220m above sea level.
During intense thunder storms, lightning strikes these dunes, and produces Fulgarites, sometimes called "fossil lightning".
A friend gave me an example today, and here it is.
Barry.
Attachment:
fraser after storm, and fulgarite 018.jpg
fraser after storm, and fulgarite 018.jpg [ 107.95 KiB | Viewed 1443 times ]
Attachment:
fraser after storm, and fulgarite 019.jpg
fraser after storm, and fulgarite 019.jpg [ 104.25 KiB | Viewed 1443 times ]
Attachment:
fraser after storm, and fulgarite 020.jpg
fraser after storm, and fulgarite 020.jpg [ 126.17 KiB | Viewed 1443 times ]


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 Post subject: Re: Fossil lightning.
PostPosted: Sun Aug 17, 2014 11:55 am 
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Location: San Francisco
Barry! Those are gems to me.
I searched for more explanation and got this from wikipedia
Wiki wrote:
Fulgurites 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 mineral grains together; the fulgurite tube is the cooled product. This process occurs over a timespan of around one second, and leaves evidence of the lightning path and its dispersion over the surface or into the earth.
Fulgurites can also be produced when the cables of a high voltage electrical distribution network break, and the wires fall onto a conductive surface beneath, in the presence of loose sand.
Fulgurites may be up to several centimeters in diameter and can penetrate deep into the soil, sometimes occurring as far as 15 m (49 ft) below the surface that was struck. One of the longest fulgurites to have been found in modern times was a little over 4.9 m (16 ft) in length, and was found in northern Florida, US.
The Yale University Peabody Museum of Natural History displays the longest known preserved fulgurite, approximately 4 m (13 ft) in length.

The color varies depending on the composition of the sand in which they formed, ranging from black or tan, to green or a translucent white. The interior normally is very smooth or lined with fine bubbles; the exterior generally is coated with rough sand particles and is porous. Fulgurites are rootlike in appearance and often show branching or small holes. Fulgurites formed in sand or loose soil are mechanically fragile, making the field collection of large specimens difficult.


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 Post subject: Re: Fossil lightning.
PostPosted: Sun Aug 17, 2014 11:56 am 
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Joined: Fri Jul 04, 2014 8:17 pm
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Location: Halifax, Nova Scotia, Canada
Very cool :D


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 Post subject: Re: Fossil lightning.
PostPosted: Fri Aug 22, 2014 2:15 am 
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Joined: Wed Jul 30, 2014 7:05 am
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Very Nice specimen! :D


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