Ammonites were squid-like guys who apparently ran out of time at the
end of the Cretaceous. What we call ammonite is their fossilized
Ammolite is the iridescent result of mineralization and pressure on
the fossilized ammonite. I am sure that I am not using the precise
term to describe the colorful appearance of ammolite, nor am I
knowledgeable enough to be specific about the “tectonics” involved.
The ammolite I’ve worked with is backed with something that looks
like black glass or slate, and is sealed with another smooth,
transparent material, maybe spinel. I guess you’d call it a triplet?
Ammolite is apparently found mostly in Canada (Alberta, I think),
although ammonites were everywhere there was ocean. It is primarily
red and green, with some yellowish bits.
Amy R. Karash