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Collecting larger iron pyrite ammonites (1/2 to 1 inch
diameter), is best
carried out on the beach under Stonebarrow Hill, as the tide goes out.
BUT...
what should you look for?
Can you see it? There is a 15mm diameter pyrite ammonite on the sand directly in front of me! There is a hint here!
Collecting very small iron pyrite ammonites (1/4 inch
diameter), is best
carried out between the boulders on the beach at The Spittles, under Black Ven,
as the tide goes out.
The best way to learn about collecting fossils, is with a
guided tour from the
Charmouth heritage Center.
also known as Fool's Gold. The reducing (anoxic) conditions in the sea-floor sediments, (and sometimes in the lower water column near the sea-floor), were produced by the large supply of organic matter from dead sea creatures. Sulphate-reducing bacteria reduced the sulphate ions in seawater to sulphide, producing the unpleasant gas hydrogen sulphide (rotten eggs) in solution. This would then have reacted with any iron available to produce the brassy-looking ferrous (Iron) Sulphide, known as Iron Pyrite or Fool's Gold. Pyrite is easily formed by decomposing organic matter when in the presence of iron.
A handful of pyrite ammonites, collected in a 2 hour period
from the beach
under Stonebarrow Hill.
If the pyritisation process goes on for too long, the ammonite
shape eventually disappears completely.
Sometimes the pyrite forms on the clay and shale to
produces 'nodules of gold'....
Depending on how 'fresh' the pyrite fossils are, they can range from either a dull-brown to a shiny-gold in colour. Unless properly treated after they have been collected, they will eventually corrode into a pile of rust, (actually into a mineral known as Melanterite, with the chemical formula FeSO4.7H2O).
The pyritised fossils should be soaked in water to remove any salt or acid, dried slowly and then coated in polyethylene glycol (PEG), or varnish, in order to preserve them. In older days, shellac dissolved in alcohol, was used.
This was the route of the Charmouth to Black Ven to Lyme Regis
coastal path. As well as the path, several gardens were also lost.
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All images copyright © Graeme Caselton
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