Brilliant Polished Pyrite Fossil Ammonite Pendant + Brass and Gemstone Bead Necklace. by Dawn Wilson-Enoch -- DesertTalismans on Etsy -The string part would make a good base for eye glass or work badge necklace.
Ammonites were free-swimming molluscs that occupied the ancient oceans. 400 - 65 million years ago
In precious Opal, larger silica spheres of about 350 µm (micro meters) in diameter give off red flashes with changes in viewing angles. The smaller spheres result in green, blue or purple flashes which cannot increase in wavelength to give a red flash. Therefore, the sizes of the 'gaps', or 'voids', determine which color is seen.