Ammonites and Ammolites: fossil variations on the spiral.
Wikipedia: A variety of ammonite forms, from Ernst Haeckel’s 1904 Kunstformen der Natur (Art Forms of Nature) 
Fossils of Ammonite shells found in museums and shops in Wales and Canada.
An ammonite sliced in half.
Polished ammonite fossil rock purchased as a souvenir in Morocco. The smallest ones are often used in jewelry.
Some ammonite shells originally contained a ‘nacre’, the pearly substance that causes the colour play you see on this modern close relative, the Nautilus shell.
The fossils retain these opalescence.
From Wikipedia: Ammolite is an opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of North America, made of the fossilized shells of ammonites.
On fossilized ‘ammolites’, this nacre turns brilliant green, blue, red and gold. This fossil Ammolite was found in a shop in Banff, Canada.
Ammonite Art
A collage of Ammonite in the Buxton Museum in England.
Pen & ink with watercolour sketch of fossil hunting in the slate in the Okanogan overlaid in Photoshop with spiral ammonite fossil image.
More on Cee’s Fun Foto Challenge: Two ‘M’s in the Word.
Batz Gallery 
Wow! Fantastic!
Fabulous
Oh this is a way cool post for this week’s challenge. 😀
I reckon too Cee