Rare Gem: Ammolite

Dragon

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Post n°1

Rare Gem: Ammolite

Post by Dragon Wed Nov 08, 2023 5:59 pm

Ammolite is an opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of North America.

It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral contained in nacre, with a microstructure inherited from the shell.

It is one of few biogenic gemstones; others include amber and pearl.

Ammolite is also known as aapoak (Kainah for "small, crawling stone"), gem ammonite, calcentine, and Korite.

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Rare Gem: Ammolite 334pu7m

Dragon

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Post n°2

Re: Rare Gem: Ammolite

Post by Dragon Wed Nov 08, 2023 6:02 pm

CC BY-SA 3.0

Ammolite

The ammolite itself is actually a very thin sheet, ca. 0.5–0.8 millimeters (0.02–0.03 inches) in thickness.

Rarely is ammolite without its matrix, which is typically a grey to brown shale, chalky clay, or limestone.

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Rare Gem: Ammolite 334pu7m

Dragon

Dragon: Senior Administrator; Posts : 10756
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Post n°3

Re: Rare Gem: Ammolite

Post by Dragon Wed Nov 08, 2023 6:06 pm

Rare Gem: Ammolite 448px-IridescentAmmonite

CC BY-SA 3.0

IridescentAmmonite

Ammolite comes from the fossil shells of the Upper Cretaceous disk-shaped ammonites Placenticeras meeki and Placenticeras intercalare, and (to a lesser degree) the cylindrical baculite, Baculites compressus.

Ammonites were cephalopods, that thrived in tropical seas until becoming extinct along with the dinosaurs at the end of the Mesozoic era.

The ammonites that form ammolite inhabited a prehistoric, inland subtropical sea that bordered the Rocky Mountains—this area is known today as the Cretaceous or Western Interior Seaway.

As the ammonites died, they sank to the bottom and were buried by layers of bentonitic mud that eventually became shale.

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Rare Gem: Ammolite 334pu7m

Dragon

Dragon: Senior Administrator; Posts : 10756
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Post n°4

Re: Rare Gem: Ammolite

Post by Dragon Wed Nov 08, 2023 6:09 pm

By James St. John

Ammolite (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.

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”)

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Rare Gem: Ammolite 334pu7m