Most people who have an interest in gemstones or nature have seen petrified wood, but fewer are aware of the many other types of fossilized organisms that can be fashioned into beautiful gems. Sometimes the whole organism is preserved as with Turitella snails, Starburst Algae, or Sea Lilies. More often, though, various parts or products are all that are preserved, such as bone, shell, eggshell, footprints, tunnels, or even dung.
Most often, the preservation occurs as the organic materials are replaced ever so slowly with mineral solutions, such as silica, which harden and take the original shape. In other cases, mud in which the structure lies is compacted and compressed over time into shale that now holds the fossil.
Particularly beautiful are the ammolites, which are the result of replacement of the thin layers of the shell of an ammonite, (an extinct, snail-like organism,) with mineral layers, which then create the phenomenon of iridescence.
There are no accepted price ranges for fossilized organisms, other than the general considerations that apply to all gems. Common items, like shark’s teeth are generally inexpensive while rarer items like fossilized ivory or dinosaur eggshell command higher prices. In any given case, specimens that have the best patterns or most complete preservation of the organism in question are most valued.