FINE DOUBLE GEM AMMONITE PLAQUE. ...

Description

FINE DOUBLE GEM AMMONITE PLAQUE
Placenticeras meeki
Upper Cretaceous
Bearpaw Formation, Alberta, Canada
The ammonites found in the oceans covering this small area of North America 65-100 million years ago are amongst the most sought-after of all fossils. All ammonites have a layer of nacreous mother-of-pearl (hexagonal platelets of aragonite) lining their shells, but only the Placenticeras sp., through the combination of millions of years of compression and the mineralization of iron, copper and silica which precipitated from the bentonite sediment of volcanic ash, have been transformed into this beautiful precious gem stone ammolite. It is one of several biogenic gemstones, like amber and pearl, and can be grouped with other shell-based marbles such as lumachella, or "fire marble", formed from the fossilized shells of clams or snails. It is far more striking than these other substance, however, and was accorded gemstone status by the World Jewelry Federation in 1981. This fantastic plaque boasts two examples, measuring 14¼ and 6 inches in diameter. The gray stone matrix provides the perfect ground to offset the shimmering display of iridescent green, yellow and red that flashes across the shells, enlivened by highlights of the much rarer blue and purple shades. The plaque itself measures 39½ x 31 inches and is presented on a custom metal display stand.

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