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Ammolite

During the great 300-million-year flowering of marine life called the Paleozoic era, a squid-like animal known as the ammonite thrived in every ocean. This mollusk made its home in giant coiled shells similar to those of the chambered nautilus that we see today. Just like the dinosaurs that emerged later in this geologic age that began 500 million years ago, the ammonite eventually suffered a species wipeout.

Today, ammonites are found fragilely fossilized in various shales all over the world. Usually what remains are dull-colored agatized shell imprints in a host material. This imprint shows the increasingly larger quarters the growing animal built for itself in spiral fashion, walling off each new dwelling space from the previous one. Occasionally, when these aragonite shell molds are lined with nacre, they exhibit a pearly iridescence. The most iridescent and best preserved of these fossils go to museums, but some are used as pendants and brooches.

Now wouldn’t you think that the nacre-coated mollusk remains found on every former sea floor from South Dakota to Tibet would have become prime gem material sometime during the 200 million years since the Paleozoic era? After all, dinosaur bones are found in a gemmy petrified state. Why not gemmified ammonite?

Well, there is at least one place where ammonite shell metamorphosed into a bona fide gem material. Called, appropriately enough, “ammolite,” it is retrieved from shale found 20 feet or so below the ground at various spots throughout Alberta, Canada. The richest of these sites, located at Lethbridge, Alberta, was discovered in 1979 and ever since has been owned and operated by Korite Minerals Ltd., headquartered in Calgary, Canada. Since the Lethbridge deposit produces at least 90 percent of the world’s ammolite, Korite could be considered a De Beers for this gem, albeit a thimble-sized version that controls the market by default rather than design.

From Shell to Shellac

Unlike most ammonites, which died and left aragonite impressions of their outer casings in the sediment at the bottom of the ocean, ammolite was transformed from shell to gem altogether. Korite’s Pierre Pare explains how:

“The empty shell fell to the bottom of the ocean. Over millions of years, a concretion formed around the shell and it became a nucleus that was sealed off from the destructive effects of water and oxygen. As this nodule grew in size, it acted like a pressure cooker to re-mineralize and re-crystallize the ammonite.”

In a superb essay on ammolite published in the January 1986 Lapidary Journal, gemologist Fred Pough described the gem’s creation as a 70-million-year makeover, during which “the deeply buried [ammonite-shell] fragments have been squeezed, compacted and marinated” in a mineral-rich mudpack. Evidently, Alberta’s mudpack formula was unique because ammonites turned to ammolite aren’t as yet found elsewhere. Too bad. This shell-reborn-as-rough is glazed with a mother-of-pearl finish so superior to any latter-day variety Pough calls it “grandmother-of-pearl.”

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Ammolite