AMMOLITE
Ammolite
is biogenic gem material from Alberta, Canada.
It has stunningly intense, iridescent rainbow colors. Ammolite is fossil shell material from Placenticeras ammonites. Ammonites are an extinct
group of swimming squid-like organisms with planispirally coiled shells (the chambered
nautilus in modern oceans is a distant relative of ammonites, but has a
similar body plan). Ammonite shells were
originally nacreous aragonite (“mother of pearl”) (CaCO3). Geologic studies have shown that ammolite gem
material formed from slight diagenetic alteration of the original ammonite
nacreous aragonite shell. Diagenesis has
significantly intensified and brightened the play of colors from the nacreous
aragonite.
Ammolite
is mined, polished, and treated by resin- or epoxy-impregnation to stabilize it. Very rarely, complete specimens of Placenticeras ammonite shells preserved
in ammolite are recovered - such specimens are exceedingly valuable (for
example, see figure 2 of Mychaluk et al., 2001).
Name & classification: Placenticeras meeki or Placenticeras
intercalare (Animalia, Mollusca, Cephalopoda, Ammonoidea, Ammonitina)
Stratigraphy & age: Bearpaw Formation,
Campanian Stage, upper Upper Cretaceous, ~70-75 Ma.
Locality: mine in the St. Mary River Valley west
or northwest of Welling and south-southwest of Lethbridge, southern Alberta,
southwestern Canada.
Ammolite (above & below) (5.5 cm across at its
widest) - diagenetically altered, iridescent Placenticeras ammonite shell material (nacreous aragonite, CaCO3)
from the Upper Cretaceous Bearpaw Formation of the St. Mary River Valley,
Alberta, Canada.
Reference cited:
Mychaluk, K.A., A.A. Levinson & R.L.
Hall. 2001. Ammolite: iridescent fossilized ammonite from
southern Alberta, Canada. Gems & Gemology 37(1): 4-25.