A Cleoniceras ammonite Pair conserved from Madagascar. These have been prepared, cut in half and polished revealing the wonders of mineralisation which takes place over millions of years. Each chamber has been replaced with calcite, quartz and sedimentary muds which have hardened into limestone, in the process absorbing rich mineral nutrients which colour to form in most cases various exotic brightly coloured jaspers, a semi-precious stone.
A few years ago off the Great Barrier reef at depths between 200 to 400 meters, sightings of the Nautilus Pompilius were made, showing the pressures these Cephalopods can attain. The Ammonites extinction is dated around 74 million years, pre the great mass extinction of around 65 million years. Ammonites are important Index Fossils, it is often possible to link the sediment layer in which they are found to specific geological time periods. The largest ammonite to date is around 2.5 meters in diameter from Germany.