Yogo sapphire

46.845833333333 - 110.31055555556Koordinaten: 46 ° 50 ' 45 "N, 110 ° 18' 38 " W

Yogo sapphires (short Yogos ) are sapphires from Yogo Gulch canyon in Montana. The canyon is located in the Little Belt Mountains in the Rocky Mountains, in Judith Basin County. The land was formerly part of the Piegan ( Blackfeet ).

Sapphires are varieties of the mineral corundum. Most Yogos have the desired for sapphires deep blue color that they owe their geological formation. In the opinion of many gemologists, who describe this color associatively as " cornflower- blue " ( " cornflower blue" ), they are among the finest sapphires in the world. They are characterized by uniform transparency and shine even in artificial light.

Since the Yogo Gulch sapphires occur in a vertically inclined magmatic Dyke, their degradation was sporadic and rarely profitable. It is estimated that at least 28 million carats are found in the soil ( 5.6 t ) Yogos. Jewelry that contain Yogos were the First Ladies Florence Harding and Bess Truman paid. Several Yogo sapphires are part of the collections of the Smithsonian Institution.

Location

The sapphires are mined in Yogo Gulch in Montana, which was at the time of discovery in Fergus County, but since 1920 by shifting the County boundaries is part of the new Judith Basin County.

Yogo Gulch and the environment, Yogo Peak, Yogo Yogo Creek and Dyke are located in the Little Belt Mountains. The gorge is located on the lower reaches of Yogo Creek, west of the Judith River. The Yogo Dyke lies west of Yogo Creek.

Etymology

The meaning of the word Yogo is unclear. Since Yogo Gulch is located in an area that was inhabited by the Piegan Blackfeet, alleged dealer, that the word " Yogo " in their language, " love" or " blue sky " mean, although there is little evidence. In modern dictionaries of the languages ​​of the Blackfeet, there is no word that " Yogo " is similar in meaning, as it is called by the merchants. The word for love is advertising " isawaanopaat ", the word for the color is blue " ótssko ", and the word for " skyward " is " sspóóhtsi ". Other meanings of the word " Yogo " has been proposed, including " Unauthorized removal ". The meaning of the word was already lost when placer gold was found in 1878 in Yogo Creek.

Mineralogy

Sapphires are a colored variety of corundum, a crystalline form of aluminum oxide, which is one of the hardest minerals. Corundum is with a Mohs hardness of 9 on the diamond, the second hardest mineral, and thus a reference mineral on the Mohs hardness scale. Corundum in most colors is known as sapphire, only red corundum is called ruby. The term " Yogo sapphire" refers only to sapphires from the Yogo Gulch.

The blue color is due to the Yogos traces of iron and titanium. Yogos are almost always blue, about two percent of Yogos are "purple" ( purple ) due to traces of chromium. Unique properties of these sapphires are that they are free and clear of uniform cavities and inclusions. They do not require heat treatment, which is often used in other sapphires, to achieve the desired blue color. Unlike Asian sapphires they show their luster even in artificial light.

The special properties due to their geological history. Most sapphires originated at low pressure and moderate temperature in geologically short period of time and therefore exhibit irregularities and uneven color. Yogos crystallized, however, under very high temperature and high pressure in geologically long time. Since Yogos occur as minerals in igneous rocks and not, as most other Sapphires, in alluvial soil, they get a perfect or nearly perfect crystal structure without inclusions or layers of paint. Point at the base of a pattern of triangles with thin rhombohedral facets that are missing from Montana in other sapphires.

The United States Geological Survey and many experts rate Yogos as " among the world's finest sapphires " ( sapphires among the finest in the world). The blanks are usually small and flat, so are stones over 2 carats rare. Approximately 10% of the cut stones are more than 1 carat. The largest blank, which was found in 1910, had 19 carats and was made into an 8 -carat stone. The largest cut Yogo has 10.2 carats.

Geology

The Yogo Dyke, containing the sapphires, consists of dark gray to green intrusive, which is known as lamprophyre. Lamprophyre is an unusual igneous rock, which has a low proportion of quartz. The rock has an irregular porphyritic structure, built into the large crystals of pyroxene and phlogopite in a fine-grained matrix. The phlogopite - crystals were used to determine the age of the Dyke and its crystallization temperature of 900 ° C. The Dyke also contains inclusions of other rock types, including sandstone, clastic sediments and gneiss. In some places the Dyke appears because of a lot of inclusions as a breccia of sandstone in an igneous matrix. A gneiss fragment as inclusion contains corundum. The sapphires are in turn surrounded by a layer of spinel, its surface is etched, pitted and rounded ( etched, pitted, and rounded ), indicating that they were not in chemical equilibrium with the surrounding lamprophyre magma. It can be concluded that the sapphire crystals developed in a previous rock, for example, in the gneisses, which was " assimilated " later by the lamprophyre magma at depth. Previous researchers had assumed that the sapphire crystallized from the magma by a necessary high aluminum content, which was made ​​possible by the assimilation of " shale " from the Proterozoic Belt Supergroup in the. These sediments occur in depth in the region.

The Yogo Dyke is a narrow strip of igneous rock lying subvertical. Its thickness varies from 0.61 to 7.9 m and extends over 8 km. The Dyke is broken into three segments and is dated to 46.8 million years after the argon dating of phlogopite. The Dyke is enclosed by sandstone of the Mississippian, which is 325-360 million years old, and other sedimentary rocks of the Madison Group and Big Snowy Group.

Reduction

At Yogo Creek in 1866 gold was found. Prospector found blue stones from 1878 in the river bed below the Yogo Dyke, but the "blue pebbles " (blue pebbles ) were detected only in 1894 as sapphires. It was discovered that they came from the rock upstream. The degradation of the sapphires started in 1895 after a rancher named Jake Hoover sent a cigar box of stones to a valuer, who gave it to Tiffany & Co. in New York. There they rated Dr. George Frederick Kunz, the leading American gemologist his time, as "the finest precious gemstones ever found in the United States " ( the choicest gems that were ever found in the United States). Hoover was bought by the main vein of a shepherd and later sold them to other investors. This results in the 1899-1920 very profitable " English mine " developed ( English mine ). Another company, the "American Mine" (American Mine) in the western portion of the Yogo Dyke, belonged successively to a number of investors, but it was less profitable and was bought by the owners of the English mine. In 1984, the reduction in a third section, the Vortex Mine.

Since most Yogos are in igneous rocks and not in alluvial soap, their degradation is difficult. High American wages increase the cost of mining in addition. It is estimated that at least 28 million carats are found in the soil ( 5.6 t ) Yogos. The Yogo Dyke is the only igneous rock be removed out of the sapphires.

Special jewelry

Several Yogo sapphires are kept in the Smithsonian Institution, Washington, DC. The earliest transfer is recorded in the annual report of the Museum of 30 June 1899, when LT Chamberlain bequeathed to the Isaac Lea gem and mineral collection two ground Yogos and 21 other sapphires. A record holder, a 10.2 carat polished Yogo is also part of the Smithsonian.

2006 bequeathed to the gemologist Robert Kane of Fine Gems International in Helena, which offers the largest selection of sapphires from Montana, 333 sapphires totaling 27.07 carats to the gem and mineral collection of the National Museum of Natural History, along with 98.48 g of 18 - karat yellow gold for making a piece of jewelry.

A representative of the Smithsonian commissioned Paula Crevoshay, to create a goldsmith from Albuquerque, New Mexico from these stones a piece of jewelry. Crevoshay chose a butterfly motif to match the natural beauty of America to honor her mother's love for butterflies and highlight the variety of colors of sapphires from Montana. She called the brooch for her mother Conchita Sapphire Butterfly Brooch known as ( Sapphire Butterfly Brooch), Conchita Sapphire Butterfly Brooch Butterfly or Montana. Most stones are from the Rock Creek, but the largest is a blue Yogo as the head of the butterfly. Other sapphires are yellow, purple, pink and orange. Crevoshay created the brooch in 2007 and put them together with Kane the curator of the Smithsonian, Jeffrey Post, May 7, 2007.

Paulding Farnham (1859-1927) of Tiffany & Co. Yogos used in some jewelry pieces that he designed for the 1900 Universal Exhibition in Paris, where Yogo sapphires received a silver medal for color and shine among all presented stones. On the Louisiana Purchase Exposition in 1904 in St. Louis, Missouri uncut Yogo sapphires received the bronze medal.

For the world exhibition Farnham also created a brooch in the shape of an iris in natural size, the Tiffany Iris Brooch, used for which he sapphires 120 Yogo and which he sold on March 17, 1900 for $ 6,906.84. In 1923, the First Lady Florence Harding was handed a ring of Montana, which was designed from Yogo sapphires and gold from Montana. 1952 gave Charles Gadsden, the person in charge of the English mine, polished Yogos to President Harry Truman, his wife Bess and their daughter Margaret.

Since the degradation of Yogos was partially operated by British companies, many Yogos were sold in Europe. Yogos may have been in the 1910s in personal collections of some members of the British Royal Family, but claims that Yogos are part of the English Crown Jewels, can be neither proved nor disproved. The claim that the stone in the engagement ring of Lady Diana Spencer and Kate Middleton is a Yogo is doubtful; It is assumed that the stone is derived from Sri Lanka.

Sapphires from Montana

The term Yogo sapphire is used for sapphires, which originate from the Yogo Gulch, while the more general term Montana sapphire (sapphire from Montana) sapphires names that are found in Montana in other places. They come in many colors, but Yogos are almost always blue. In Yogo Gulch only a few rubies have been found. In Montana, more jewelry stones are made ​​of sapphire produced than in any other state of the United States. 1969 sapphire and agate were declared Montana's "state gemstone " (state gem).