Ammolite

Ammolite is a rare opalescent gemstone. It is mainly found on the eastern slopes of the Rocky Mountains, and consists of the fossilized remains of ammonites. Ammolite is also available under the trade names Calcentin or Korit. In the languages ​​of the indigenous there Blackfoot tribes of the stone Aapoak is called (small, crawling stone in the language of Kainah due to the play of color ) or Iniskim ( buffalo stone).

Formation

During the Cretaceous period in North America was a large subtropical inland sea, the Western Interior Seaway. Due to continental drift, the younger part of the Rocky Mountains unfolded, while the sea gradually disappeared. In this warm sea lived under other the Ammonites Placenticeras meeki and Placenticeras intercalare and rare Baculites compressus.

Their shells fell after the death from the sea floor and were covered by clay (bentonite ). In these bentonite sediment layers, the Ammonites were largely crushed, but the shells were preserved. These shells were partially made ​​of nacre, so fine plate-like aragonite crystals that are embedded in a protein matrix.

Most fossilized shells of aragonite was removed because it is more soluble than calcite, for example in the surrounding rock. The resulting voids were later often filled by other materials such as calcite or pyrite rare or remained hollow. At temperatures above 400 ° C, the unstable aragonite transformed to the more stable calcite. Therefore fossils with preserved aragonite are particularly rare.

When the Ammonites enclosures from which Ammolite arose, the process was somewhat different. The aragonite was retained, this was mainly due to the coverage by impermeable volcanic ash that came from eruptions of volcanoes forming the Rocky Mountains. Simultaneously, the ammonites containing layers came in not to great depths, so that they are not heated above 400 ° C. During diagenesis, trace elements such as iron and magnesium wandered into the shells.

Only rarely completely well-preserved ammonites are found in which the suture patterns can still be seen. Up to 90 cm large ammonites have been found, but usually the opalescent ammonites are much smaller.

Properties

Ammolite is composed mainly of aragonite, which is derived directly from the original mother of pearl in the shells of ammonites. In addition to aragonite occur calcite, quartzite, pyrite and other minerals in varying proportions. In the shell itself are a number of trace elements before (aluminum, barium, chromium, copper, iron, magnesium, manganese, strontium, titanium, and vanadium).

Ammolite located ( such as aragonite ) in front of the rhombic crystal system, but shows a slightly greater hardness 4.5 to 5.5 and density of from 2.60 to 2.85 g / cm ³ when the latter. Ammolite is optically biaxial, the refractive indices of the Canadian material ( at 589.3 nm, yellow sodium light ) are: α 1.522; β from 1.672 to 1.673; γ from 1.676 to 1.679, and optically negative. Under UV light, show some Ammolite a mustard-yellow fluorescence.

Based on the obtained from the original mother of pearl layer structure of aragonite shows opalescence. Caused by the interference in thin layers, such as soap or oil in spots, not by a natural color or light refraction. The color is dependent on the layer thickness: thick layers provide red and green interference colors, thin layers also supply blue and yellow tones.

Like the original shell is the Ammolite only in a very thin ( 0.5-0.8 mm) layer before, this is usually located on a gray - brown matrix of slate, calcareous marl, or limestone. The rock was compressed by lying sedimentary layers, so the Ammonites are usually crushed, so as to form numerous cracks in the thin layer. This crack texture is sometimes described as dragon hide or church glass window-like. Ammolite from deeper layers may be completely smooth, or even show a ripple- like surface.

Locations

Ammolite is found mainly in the Bearpaw formation that extends from the Canadian provinces of Alberta and Saskatchewan to Montana in the USA. The best gemstone qualities can be found here on the eastern slopes of the Rocky Mountains in southern Alberta.

A similar material is Lumachella, a marble from fossilized shells and snails, which is found in Italy and Austria. Lumachella opalesziert only partially and is not as brilliant as Ammolite due to the bright substrate. The marble is therefore not or very rarely used for jewelry purposes. Like other marble used in mosaics or as cladding panels.

Most commercial mining operations for Ammolite are located on the banks of the river St. Mary, a tributary of the Saskatchewan River, in the area of ​​the cities Cardston and Lethbridge. Of great significance is the reserve of Kainah Indians, where about half of all Ammolitablagerungen be found.

Even in Madagascar, Russia and Somerset / England Ammolite can be found.

Extraction in Kainah Reserve

The most important company for the commercial extraction of Ammolite is Korite International, which operates mainly in the reserve of Kainah since its founding in 1979. The Company will pay the tribe a usage fee for the degraded of their areas.

The extraction is done on flat surface mines, which are dug with excavators. The extracted material is screened for its possible Ammolitgehalt. The pits are scanned directly from non- employees on lying on the surface Ammoliten, which are then sold to Korite International. Approximately five percent of the degraded Ammolits are suitable for processing into jewelry.

The Ammolitablagerungen are layered: called the top of these layers, K - zone, about 15 m below the surface and extends 30 m in depth. The ammolite within this layer is surrounded by siderite concretions and is usually broken with a lot Committee. It is the most common and generally the least valuable Ammolite.

Twenty feet below can be found then the Blue Zone. In this 65 m thick layer of Ammolite is usually surrounded by a thin layer of pyrite rather than siderite. Ammolite this is something of flat layers which are less broken. Because of this better quality and rarer because of the great depth recovery of these Ammolite is the most valuable.

By 2003, Korite International is only 30 acres ( about 12 ha) had reduced the Kainah deposit. As part of its agreement with the parent company must fill the exploited areas, and ensure that the environment is not affected permanently disadvantageous. The company employs about 60 people, most of them are Kainah, falls for the tribe per year from a net profit of about 150,000 200,000 CAD $ to. About 90 percent of the world annual production of Ammolite jewelery stones mined there.

Use as a gemstone

Ammolite is one with amber and pearls in the biogenic gemstones. In 1981, along with a launch of the then relatively unknown stone engaging in a larger open pit by the mining company Korite International. In 2004, ammolite was named official gemstone of the Province of Alberta.

Ammolite is considered the rarest organic gem. In its raw state it is traded at prices from 30 to 65 USD per carat ( $ 150-325 / g). Because it is soft and sensitive, it requires a special processing, which is only a few experts precisely known. This processing makes the stone more resistant and stronger in color. In addition to the cutting in the desired shapes of the stone to be polished, since a very rough surface which scatters light and thus shows only duller colors. A coating with a resin provides for a stabilization of thin leaves, where Ammolite is present.

History

Compared with most other gemstones, Ammolite has a short history: Greater interest only achieved the stones in the seventies, after they had come in 1969 in small quantities on the market. The Kainah tribe knew the stone as Iniskim ( buffalo stone) and believed for a long time that the stone has magical powers that help in the hunt for buffalo and attract buffalo. In addition, the stone should possess healing powers, so that the stones were used in ceremonies of medicine men.

In the late nineties, practitioners of Feng Shui began to apply Ammoliten as influential. The stone is said to have the power to increase by improving the flow of chi energy well-being and detoxify the body. The so-called Dragonscale (English Seven Color Prosperity Stone) should with any color affect the carrier in various positive ways: a combination of ruby red, emerald green and amber is therefore highly sought which colors are to promote growth, wisdom and health.

Japan is the largest market for ammolite. One reason for this is replacement function for the to rare black opal, the other is the use in Feng Shui. The second largest market is Canada: Ammolite is used by both artists, who sell their creations to tourists in Banff National Park, as well as jewelers. In the southwestern United States, it is used by the Zuni and other Native American artisans.

Processing

Unlike opals Ammolite is completely mineralized and contains no water. Therefore, it can not dry out like the opal and cracking. Nevertheless, Ammolite can be damaged by the environment. This is mainly due to its low hardness. Even with the usual dust contained in tiny grains of sand ( quartz with the Mohs hardness = 7) can cause scratches. The fact that the Ammolite is present only in thin, delicate leaves, increases the risk of damage from flaking of the leaflets.

Only a small proportion of Ammolite has such a high quality that they would not be treated except for the cutting and polishing. Most stones are impregnated with epoxy resin to stabilize or other synthetic resins prior to cutting to ensure that the sensitive Ammolitschicht does not flake off. Thus, formation of new cracks can be prevented, however, existing tears can no longer be cured. In addition, the coating is a protection against scratching. This impregnation technique was developed over several years by Korite International in collaboration with the Alberta Research Council and was first introduced in 1989 in the market, allowing considerably more Ammolite are available as semi-precious stones.

After polishing, the Ammolitschicht is only 0.1 to 0.3 mm thick. Only very rare and valuable Ammolite are still thick enough to together with a thin layer (less than 1.5 mm) of the original matrix to be to be sufficiently stable and thus used as a gemstone. Most, however, stones must still be stabilized by being assembled into doublets. The thin Ammolitschicht is placed on a dark, stable support. The carrier can be either a dark matrix in which the Ammolite is usually embedded as well as black onyx or glass. For especially thin Ammolitschichten the duplicates to be expanded: a hard transparent cover is still stuck on the Ammolite. This usually convex cap can be made of synthetic spinel, corundum or quartz or even glass. A convex cap acts as a lens, and increases the angular range in which the play of colors can be observed.

Ammolite is usually designed in free-form cabochons and set in gold, diamond accents form. Because of the sensitivity Ammolite is ideally used in pendants, earrings and brooches. As Ammolite Ring Stone should only triplettiert be used with a fixed cap (eg, spinel). But enough small, fully-polished Ammoliten be used as jewelry. To care only warm water should be used with a mild soap, ultrasonic baths can destroy the stone.

Quality designations

The quality of Ammoliten that are used as gemstones, is A- rated on a letter system of good AA over A , A to bad. This system is not yet standardized and some vendors use their own systems. This classification and hence the value of an ammolite gemstone is determined by the following criteria:

Imitations

Ammolite can not be easily imitated yet often this happens. However, he is even offered as an imitation of the more valuable black opal. However, similarities show some other substances. So the labradorite shows a bluish opalescent. The blue and violet, however, is more intense than that in Ammoliten. Opal imitations like the Slocum Stone show a play of color in smaller spangles. A further distinction is that ammolite itself is opaque, in the possible imitations, the material is more translucent.

A possible imitation is through the nacre of abalone. These preferably green blue opalescent snail is beneficial because it is massively collected for consumption. The shell structure is however striking: curved, blue, green and pink opalescent bands are separated by dark brown lines from Conchiolin. The splendor of this nacre is rather silky compared with the more glassy gloss polished Ammolits. The colors do not match. Nevertheless, there are Ammolite imitations of colored abalone nacre dublettiert with a cap made ​​of synthetic quartz. These imitations are the most deceptive imitations and are also manufactured as opal imitations. Under the microscope, but accumulations of the colorant and air bubbles between quartz and mother of pearl can be seen.