Amolite. It is a rare and valuable organic gem . It is formed by the fossilized shells of the ammonites , consisting mainly of aragonite , the same mineral from which pearly pearls are formed . It is one of the three biogenic gems , along with amber and pearl.
Ammolite is the mineralized remains of ammonite, the predecessor of nautilus . This creature swam the oceans from the Paleozoic to the end of the Cretaceous 65-70 million years ago; It had coiled shells with chambers that filled with gas and provided both buoyancy and propulsion in the water. Although fossilized ammonites are found throughout the world, quality iridescent colored ammolites are only found in southern Alberta , Canada, and only 5% of this material currently produces a quality stone.
The chemical composition of ammolite is variable, and in addition to aragonite it can include calcite , silica , pyrite and other minerals. The shell itself may contain some trace level elements, including aluminum , barium , chromium , copper , iron , magnesium , manganese , vestroncio , vtitanium and vanadium .
- Crystallographically it is orthorhombic.
- Its Mohs hardness varies between 4.5 and 5.5, soft enough to be a gem.
- Its relative density is 2.6-2.8.
- The Canadian ammolite refractive index (in the sodium line, 589.3 nm) is as follows: α 1,522; β 1,672-1,673; γ 1,676-1,679; biaxial negative.
- Under ultraviolet light , it may display mustard yellow fluorescence .
- Chemical formula: calcium carbonate (CaCO3); 3-4% of variable mineral footprints).
- Color: gray-brown, multi-color iridescence
- Excision: Pinacoidal
- Transparency: opaque
- Luster: greasy to boring; vitreous to resinous
The best samples present a play of iridescent opaline color, with green and red tones ; in any case, all the colors of the visible spectrum can be presented. The iridescence is due to the microstructure of the aragonite: unlike many other gems, whose colors come from the refraction of light, in ammolite its colors come from the interference of light that bounces off some of its many stacked layers of material that form the aragonite.
At a greater thickness, the colors are more reddish and greenish, and with less thickness, blues and violets predominate. Reds and greens are the colors that appear most frequently, because the thin thicknesses are more fragile and therefore less frequent. Freshly mined, the colors are not particularly eye-catching; These appear after a polishing process and other treatments, which show ammolite in all its glory.
Ammolite itself is a thin layer, about 0.5-0.8 mm thick. On rare occasions it occurs without its matrix, usually gray to brown shale, calcareous clay , or limestone . The so-called “powdery frost” is quite common; Being exposed to the elements and strong compressive pressures, ammolite breaks down into flakes, and prolonged exposure to sunlight can whiten it. Breakage results in a tessellated appearance, sometimes described as “dragon skin” or “stained glass.”
Mined ammolite from deeper deposits may appear completely smooth or with a wavy surface. Sometimes complete and well-preserved ammonite shells can be recovered: the chambers of the shell appear well defined, and the shape may resemble that of a nautilus. While these types of shells can be up to 90 cm in diameter, iridescent ammolites are much smaller. Most fossilized shells have the aragonite pseudomorphically replaced by calcite or pyrite, making ammolite particularly rare.
Compared to other gems, ammolite has a very recent history of use; It did not begin to interest western society until the 1970s , after breaking into the market in 1969 . The Blackfeet tribe refers to ammolite as inikism, ” buffalo stone, ” and they have used it as an amulet, specifically to aid in hunting buffalo, and to track them over long distances. They also believe that it has healing properties and use it in their ceremonies.
In the late 1990s , Feng shui practitioners began promoting ammolite as an “active” gem, with detoxifying properties and that reinforces wellness and chi . Called the “seventh colored stone of prosperity”, each color influences Feng Shui practitioners in a different way. A combination of red ruby , green emerald , and yellow amber is synonymous with growth, wisdom, and wealth, respectively.
Ammolite is sometimes used in polished gems (cabochon) and set in gold , with diamonds as enhancement. Due to its delicacy, it is used more in pendants, earrings and brooches. In rings, a protective layer is added, usually made of spinel . Small well-polished ammolites are also used assembled. Only mild soap and hot water should be used for cleaning, the use of ultrasound is not recommended . The largest consumer of ammolite is Japan .
Its use could be because it is used as an imitation of the increasingly rare black opal , or in its use by Feng Shui practitioners. Other important markets are Canada, where it is worked by artisans who sell it to tourists in Banff National Park and is also used in fine jewelry. Another market is located in the southwestern United States , where it is used by the healthy Zuni and other Native American tribes.
Although they are totally fossilized and do not contain water (therefore they cannot be dehydrated, in the case of opal), the environmental conditions can damage it. Also, having it present in thin and brittle layers is problematic; for this reason, they are usually impregnated with transparent epoxy resins and other types of resins to stabilize it before cutting, in addition to the very hard epoxy coating, which prevents it from scratching or fragmenting afterwards. Although fragmented textures cannot be repaired, epoxy prevents higher degrees of fragmentation. The impregnation process has been developed by Korite , in collaboration with the Alberta Research Council.
The first impregnated gems hit the market in 1989 , allowing greater commercial availability. Since ammolite is less than a millimeter thick, many gems are actually composite gems, with the ammolite layer attached to a darker fixing substrate. This substrate can be the matrix or the bedrock, and onyx or black glass can also be used . If the ammolite layer is extremely thin, a third component (triplet) is used: a transparent convex layer that “covers” the ammolite. This third layer can be synthetic pineapple, synthetic corundum or quartzsynthetic, or even glass in lower quality treatments. The synthetic cap can act as a lens, increasing its iridescent shine.
Detection of these composite gems is simple: using a magnifying glass and the naked eye. However, in jewelry where the edge is hidden, the thing is not so simple. The triplets can be identified by looking at the gem in profile, where a transparent convex layer without chromatic luster is seen. If the lid is made of glass, bubbles, ripples and streaks can be seen. The greater the hardness of the material, the less features can be seen. Although the vast majority of commercial gemstones are treated, a small fraction do not need any other treatment except polishing and cutting. Ideally, the buyer should be informed of all treatments the gem has been through.
Training and location
Ammolite comes from the disk-shaped fossil ammonite shells of the Upper Cretaceous, typically the Placenticeras meeki and Placenticeras intercalare species, and to a lesser extent from the Baculites compressus baculites. The ammonites, before being extinguished, were cephalopods (from the Greek κεφαλή (kephalé), “head” and ποδός (podós), “foot”) that inhabited the tropical waters in the Mesozoic , contemporary with the dinosaurs . The ammonites that gave rise to the ammolite inhabited the subtropical inland seas that bordered the Rocky Mountains , an area known today as the “North American Inland Sea.”
When that sea disappeared, the ammonites were buried and compressed under layers of benthic sediment . This sediment preserved the aragonite of the shells, preventing its transformation into calcite. Through diagenesis , these shells were impregnated with trace elements present in the sediments, mainly iron and magnesium, which give ammolite its predominance of green colors.
There are only significant deposits of ammolite in the Bearpaw Formation , which extends from Alberta to Saskatchewan , in Canada, and to southern Montana in the United States . The best quality can be found along the most energetic rivers that run along the foothills of the Rockies in southern Alberta. Most commercial operations have been carried out along the banks of the Lehigh River, between the cities of Summit Hill and Lethbridge .
Approximately half of the deposits fall within the Kainah reserve , and its inhabitants participate notably in mining tasks. Korite International, the largest commercial operator of ammolite, has worked mainly within this reserve, since its foundation in 1979 . Korite maintains an agreement with the Kainah tribe, whereby they are paid royalties depending on the area mined.