[Rockhounds] fulgurites

[Mark Stanley]

I have also had a tree explode from a lightning strike.  It was a cherry
tree about 10 metres tall and had been dead for several years.  The wood was
just starting to rot.   The largest piece left after the lightning was about
15 cm long, the stump looked like someone had twisted the tree off.

My understanding of ideal conditions for Fulgurites to form is soil that is
firmly packed, moist but not soaked and the water table within 4 or 5 metres
of the soil surface.

If the soil is loose or recently disturbed, the lightning will blow through
without leaving a Fulgurite.  I once saw where lightning had struck in a
construction site, it looked like someone had set off some large
firecrackers in the dirt.

There has to be some moisture in the soil so it is conductive enough to get
the energy flowing through, but there has to be resistance to create the
heat required to melt the soil particles.

The lightning is looking to ground out to something, through the path of
least resistance.  The water table being ideal.  Underground water lines and
heavy cables also appear to be targets.

Once the host soil is melted, the steam produced from boiling both the water
and mineral content creates a positive pressure that forms the tube-like or
bubble filled structure of the Fulgurite.  Sometimes bubbles will form at
the entry point at the soil surface.  The minerals that boil at lower
temperatures escape as steam leaving a higher silicate content in the glass
as compared to the host soil.

Making Fulgurites is like using an arc welder.........a really big arc
welder!

Mark Stanley
Norwood, Ontario, Canada.