Ammolite - SOLD 2.66" with Stand Gem Quality Fossil
Ammolite - SOLD 2.66" with Stand Gem Quality Fossil
Please Note: ALL ammolite specimens will exhibit multiple colors depending on the angle of the light. The color choices reflect the dominant color of each piece.
Ammonites are an extinct group of cephalopods that entered the fossil record 400 million years ago. They survived several mass extinction events, including the Permian–Triassic "Great Dying" which wiped out 96% of all marine species. They finally succumbed during the Cretaceous-Paleogene extinction event 66 million years ago, which also wiped out the dinosaurs.
As with other mollusks, the shells of ammonites had an inner layer known as the nacre or "mother of pearl". The nacre is rich in aragonite, a crystal form of calcium carbonate, which produces an iridescent sheen. Over tens of millions of years, aragonite tends to convert to calcite, the most stable form of calcium carbonate. However, in the Bearpaw Formation, the fossils have undergone a unique process of mineralization that both preserved and intensified the natural aragonite resulting in a colorful gemstone we call Ammolite.
This specimen is a 2.66" fragment of ammolite from the Bearpaw Formation of southern Alberta, Canada. The specimen ships with a stand for display as well as a small information card that also serves as the certificate of authenticity.
📸 An artist's depiction of an ammonite swimming through the prehistoric sea
MORE ABOUT AMMONITES & AMMOLITE
ESTIMATED AGE : c. 110,000,000 years old
📸 A sample Sutured Shell Ammonite
A Perfect Spiral
Ammonites are an extinct group of cephalopods which entered the fossil record 400 million years ago. They survived several mass extinction events, including the Permian–Triassic "Great Dying" which wiped out 96% of all marine species. They finally succumbed during the Cretaceous-Paleogene extinction event 66 million years ago, which also wiped out the dinosaurs.
The size of ammonite shells range from sub-centimeter dwarf species to giants nearly three meters in diameter. Most iconic shells exhibit a nearly perfect logarithmic spiral.
How these creatures lived is of intense interest to science as ammonites likely played a vital role in the food chain in the ancient seas. Evidence exists to suggest that ammonites were a prime food source for Mosasaurs and fishes, while other studies suggest the "bite marks" were created after death by limpets or even by other cephalopods.
The Late Cretaceous was a time during which the interior of North America was covered by the Western Interior Seaway which extended from the Arctic Ocean to the Gulf of Mexico. As mountains rose in the west, they were eroded, and rivers draining eastward deposited their sediments into this interior sea some 70 - 75 million years ago.
📸 A beautiful, iridescent ammolite fragment
Making a Rainbow Fossil
These waters teamed with life, particularly Cretaceous ammonites, including the most common fossils: Placenticeras meeki and P. intercalare. Both of these species are important sources of Ammolite.
Today these predominantly dark-colored marine shales form the Bearpaw Formation of southern Alberta. Interspersed between layers of shale, silt and fine sand are specific layers containing concretions. These are formed as sediment surrounding a nucleus, such as an ammonite shell, are cemented by the eventual precipitation of calcium carbonate. The vast majority of commercial Ammolite is derived from such concretions.
The Ammolite gemstone is formed as a result of alterations undergone by sediment following deposition, a process known as diagenesis. During this lengthy 70 million year process the aragonite of the ammonite shell was not converted to calcite as would be expected; the latter being the more stable form of calcium carbonate.
📸 A variety of different ammonoid shells
How these creatures lived is of intense interest to science, as ammonites likely played a vital role in the food chain in the ancient seas. Evidence exists to suggest that ammonites were a prime food source for Mosasaurs and fishes, while other studies suggest the bite marks on their remains were created after death by limpets or even by other cephalopods.
Many thousands of distinct species make up the long-lived ammonoid subclass. Though most ammonite shells are the classic spiral, there are also straight and gastropod-like shells and even some shells that are partially uncoiled. The surface of the shells also vary quite widely, from smooth to wildly thorny.
Ammonites were an incredibly diverse and plentiful group of animals that survived for hundreds of millions of years and lived all across the planet. Their rapid diversification and tough, rocky shells means there are many different and easily identifiable species in the fossil record. Because of this, scientists can use them to easily identify the age of other fossils and geologic deposits found in the same layer of the ammonites. They're a welcome sight to the eyes of any inquisitive geologist!
Aside from their complex shells, there is little direct evidence regarding the appearance of ammonites due to the absence of soft tissue fossils. However, many scientists believe ammonites had bodies similar to that of the present-day Nautilus.
📸 A logarithmic spiral in a natural ammonite fossil
Ammonite shells grew in a natural spiral and made a consistent, mathematically significant pattern. This special shape is known as a logarithmic spiral.
The main property of a logarithmic spiral is that the shape of the spiral is unaltered as it increases in size. Each turn is a pure geometrical progression of the last with a common ratio. This form is found in many natural phenomena, from the shape of galaxies to patterns on sunflower heads.
Staaf, Danna. Monarchs of the Sea: The Extraordinary 500-Million-Year History of Cephalopods. The Experiment, 2020.
Tsujita, Cameron J., and Gerd EG Westermann. "Were limpets or mosasaurs responsible for the perforations in the ammonite Placenticeras?." Palaeogeography, Palaeoclimatology, Palaeoecology 169.3 (2001): 245-270.
Moulton, D. E., A. Goriely, and R. Chirat. "The morpho-mechanical basis of ammonite form." Journal of theoretical biology 364 (2015): 220-230.
Lemanis, Robert, et al. "A new approach using high-resolution computed tomography to test the buoyant properties of chambered cephalopod shells." Paleobiology 41.02 (2015): 313-329.
Landman, Neil H., and Susan M. Klofak. "Anatomy of a concretion: life, death, and burial in the Western Interior Seaway." Palaios 27.10 (2012): 671-692.
Cochran, J. Kirk, et al. "Effect of diagenesis on the Sr, O, and C isotope composition of late Cretaceous mollusks from the Western Interior Seaway of North America." American Journal of Science 310.2 (2010): 69-88.
Mychaluk, Keith A., Alfred A. Levinson, and Russell L. Hall. "Ammolite: iridescent fossilized ammonite from southern Alberta, Canada." Gems & Gemology 37.1 (2001): 4-25.
Tsujita, Cameron J., and Gerd EG Westermann. "Ammonoid habitats and habits in the Western Interior Seaway: a case study from the Upper Cretaceous Bearpaw Formation of southern Alberta, Canada." Palaeogeography, Palaeoclimatology, Palaeoecology 144.1-2 (1998): 135-160.