Ammolite

Ammolite is the fossilized nacre or Mother of Pearl of the once living ammonite.  It is a very unique natural phenomenon that results in firey colors similar to opal.  Fossil ammolite is also know as aapoak, calcentine, korite, ammonite shell, gem ammolite, or gem ammonite.  Ammonites, once the main predators of the ocean became extinct 60-70 million years ago.  Their closest living relative is the modern nautilus.  Over millions of years the shell of the ammonite has been transformed into amazing colors of ammolite that dazzle the beholder.  Similar to firey opal, the iridescent colors flash and change colors with the slightest change of viewing angle.  It is considered to be the rarest gemstone on earth and only one of three organic gemstones; the others are pearls and amber.  Never having been successfully created in the lab, it is one of the very few gemstones that is not ever man made.

The colors in ammolite are not caused by refraction, like most gemstones, but they result from interference with the light reflected back to the viewer from the stacked layers of thin platelets in the aragonite.  These layers that make up ammolite are very thin.  I have seen it from 1-2 millimeters thick to 0.5 - 0.8 millimeter, and it can actually be one a few hundreds of millimeter after polishing.  The thicker layers of aragonite produce red colors, while thinner layers are green, then blue, and purple.  Blues and purples are very rare and more valuable.  The thin delicate sheets in which ammolite occurs can flake and chip in their natural state, and for these reasons, many times the material is impregnated with a clear epoxy or other synthetic resin to stabilize ammolite prior to cutting.

The way the colors play when ammolite is held in your hand and rotated slightly is very dramatic.  It is absolutely stunning to see the colors change from red to green and back again.  This is called chromatic shift and rotational range.

Chromatic shift describes how the colors change when the angle of the light hitting the gem varies, or with a slight difference in the viewing angle.  The higher the grade material, the more change in color you will see.

Rotational range relates to how far the gem or fossil (yes, whole fossils can be covered with this gemstone!) can be turned while still maintaining its play of color; the best gems will rotate 360 degrees and still show color.

The brightness of colors and iridescence depends on the preservation of the nacreous shell, and how fine and orderly the layers of aragonite are.  Of course, the quality of polish and any impurities are also factors.  Cracking and flaking  reduces the value, and the most sought after ammolite has large areas of colors.  Multiple bright colors being most valued.

In cut gemstones, ammolite is sometimes treated similarly to precious opal and bonded to a backing stone or matrix.  This is termed a doublet.. Also, it can be made into a triplet with three layers:  the backing stone, then the ammolite, and then a cap of either synthetic or natural stone, including:  spinel, corundum, quartz, or glass.  The cap act as a lens and has the effect of enhancing the ammolite's iridescent display. 

I hope that you have the opportunity to see ammolite in person.  It is one of the most beautiful things on earth.  Please visit our eBay store:  Cerelles-fossils-collectables or fossilsrare, which is also our eBay store.  Ammonites