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Arnioceras Semicostatum Ammonites 190mm


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A Good British Ammonite commune, the ammonite boulder containing twenty-two fossils conserved by many hours of highly skilled and technical preparing. The ammonoid shells sympathetically cleaned out of the surrounding matrix (fossil limestone seabed), this has produced a unique and aesthetically pleasing naturally formed prehistoric curiosity. Read the fuller report below...

Genus: Arnioceras semicostatum ammonite commune block.
Origin: Robin Hoods Bay, Whitby, North Yorkshire, England.
Geological location: Lower Sinemurian Lias, semicostatum zone, (described by Young and Bird)
Geological Age: Mesozoic era, early Jurassic, approximately 199 to 191 million years ago.

Commune Block measurements.
Height: 19.0 cm
Width: 14.5 cm
Depth: 6.5 cm

In mount measurements.
Height: 24.8 cm
Width: 14.5 cm
Depth: 7.5 cm

Arnioceras (largest) measurement.
Diameter: 3.5 cm
Depth: 0.8 cm

Approximate commune block weight: 1.657 Kg

Approximate overall weight: 1.942 Kg

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The ammonite block is a fascinating study specimen while also having much aesthetic charm. The naturalistically positioned ammonites contained in the original limestone boulder, the boulder or nodule polished verso, with a smooth, tactile finish. The ancient boulder was once part of the fine silts of a Jurassic seabed, transformed into solid limestone by pressure and time.

Discovering an ammonite block of such rarity and preserved quality, completeness and size is an uncommon event. Add to this the excellence of the preparation and you have a highly collectable British fossil commune block. Exhibiting excellent preservation to each specimen ammonoid shell, along with attractive colour, with calcite variations which have developed within the cephalopods shell and fossilised over millions of years. Providing an interesting insight into the internal morphology of the species. All these factors put this ammonite block in the upper bracket of British discoveries of this type.

Revitalising these fascinating, extinct marine animals, the phragmacones (exoskeleton-shell) and presenting them in a dramatic way, makes them perfect for collectors or interior designers. Ammonites are becoming increasingly more difficult to gain, particularly the best of the best, from the fossiliferous coasts of the United Kingdom. Our shores may crumble inexorably towards the sea, creating landfalls and new opportunities for collecting, however, the types here of such rarity and quality remain in short supply. Laborious collecting and preparation techniques make the extraction arduous and time-consuming, an all too common fact of fossil collection today in the ever developing and changing environment of coastal Britain.