PRECIOUS GEM AMMONITE. ...

Description

PRECIOUS GEM AMMONITE
Placenticeras meeki
Upper Cretaceous
Bearpaw formation, Alberta, Canada
Ammonites that lived in the oceans covering this small area of North America 65-100 million years ago are among 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 was accorded gemstone status by the World Jewelry Federation in 1981 and is one of several biogenic gemstones, like amber and pearl, grouped with other shell-based marbles such as lumachella, or "fire marble", which is formed from the fossilized shells of clams or snails. This exquisite example, of elegant size, is presented on its natural grey stone matrix, a perfect ground to offset the amazing shimmering display of iridescent orange, green, yellow and red that flashes across the fossil shell, enlivened by highlights of the much rarer blue and purple shades. The ammonite itself measures 12 5/8 inches across and the matrix is 18 x 16½ inches, displayed on a metal stand.

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