Sapphire (yogo)

from Wikipedia, the free encyclopedia
Yogo sapphire, 0.65 carat, AAA quality

Coordinates: 46 ° 50 ′ 45 "  N , 110 ° 18 ′ 38"  W.

Map: Montana
marker
Yogo Gulch, Montana​
Magnify-clip.png
Montana

Yogo sapphires ( Yogos for short ) are sapphires from the Yogo Gulch canyon in Montana . The gorge is located in the Little Belt Mountains in the Rocky Mountains , in Judith Basin County . The land used to belong to the Piegan ( Blackfeet ).

Sapphires are varieties of the mineral corundum . Most yogos have the deep blue color desired for sapphires, which they owe to their geological origin. According to the assessment of many gemologists who associate this color with "cornflower blue", they are among the highest quality sapphires in the world. They are characterized by uniform transparency and shine even in artificial light.

Since the sapphires in Yogo Gulch occur in a vertically inclined magmatic dyke , their mining has been sporadic and rarely profitable. It is estimated that at least 28 million carats (5.6 t) of yogos can still be found in the ground. Jewelry containing yogos was gifted to First Ladies Florence Harding and Bess Truman . Several Yogo sapphires are part of the collections of the Smithsonian Institution .

location

The sapphires are mined in Montana in Yogo Gulch, which was in Fergus County at the time of discovery , but has been part of the new Judith Basin County since 1920 due to a shift in county boundaries.

Yogo Gulch and the surrounding area, Yogo Peak, Yogo Creek and Yogo Dyke are located in the Little Belt Mountains.

Topographic map of the mining region in the Little Belt Mountains ( Sapphire Mine, lower center; United States Geological Survey , 1902)

etymology

The meaning of the word yogo is unclear. Because Yogo Gulch is in an area inhabited by the Piegan Blackfeet, traders claimed that the word “yogo” in their language meant “love” or “blue sky”, although there is little evidence of this. In modern blackfeet language dictionaries there is no word that resembles “yogo” in one meaning as it is called by the traders. The word for courtship is “isawaanopaat”, the word for the color blue is “ótssko”, and the word for “heavenward” is “sspóóhtsi”. Other meanings of the word “yogo” have been suggested, including “ unauthorized removal ”. The word meaning was already lost when soap gold was found in Yogo Creek in 1878.

mineralogy

Yogo sapphire, 0.43 carat, pear cut

Sapphires are a colored variety of corundum, a crystalline form of aluminum oxide that is one of the hardest minerals. With a Mohs hardness of 9, corundum is the second hardest mineral after diamond and therefore a reference mineral on the Mohs hardness scale. Corundum in most colors is called sapphire, only red corundum is called ruby . The term “Yogo sapphire” refers exclusively to sapphires from the Yogo Gulch.

The blue color of the Yogos goes back to 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 of voids and inclusions and are uniformly clear. They do not require the heat treatment that is often used on other sapphires to achieve the desired blue color.

Purple Yogo Sapphire, 0.37 carat, brilliant cut

They owe their special properties to their geological history. Most sapphires were formed in a short geological time at low pressure and moderate temperature and therefore show irregularities and uneven color. Yogos, on the other hand, crystallized under very high temperature and high pressure over a long period of time. Since yogos occur as minerals in igneous rock and not, like most other sapphires, in alluvial soil , they have a perfect or almost perfect crystal structure without inclusions or layers of color. At the base they show a pattern of triangles with thin rhombohedral facets that are missing in other sapphires from Montana.

The United States Geological Survey and many experts rate Yogos as “among the worlds finest sapphires” (among the highest quality sapphires in the world). The blanks are mostly small and flat, so stones of more than 2 carats are rare. Approximately 10% of the cut stones are more than 1 carat. The largest blank found in 1910 was 19 carats and was made into an 8-carat stone. The largest cut yogo is 10.2 carats.

geology

The Yogo Dyke, which contains the sapphires, is composed of dark gray to green intrusive rock known as lamprophyr . Lamprophyr is an unusual igneous rock that has a low proportion of quartz . The rock has an irregular porphyry structure in which large crystals of pyroxenes and phlogopite are built into 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 types of rock, including sandstone , clastic sediments, and gneiss . In some places the dyke appears as a breccia of sandstone in an igneous matrix because of a lot of inclusions . A gneiss fragment as an inclusion contains corundum. The sapphires are in turn surrounded by a layer of spinel , their surface is etched, pitted, and rounded, which indicates that they were not in chemical equilibrium with the surrounding lamprophyre magma. From this it can be concluded that the sapphire crystals were formed in an earlier rock, for example in the gneiss, which was later "assimilated" by the lamprophyr magma in the depths. Earlier researchers had assumed that the sapphire crystallized from the magma due to a necessary high aluminum content, which was made possible by the assimilation of "shale" from the Proterozoic in the Belt Supergroup . These sediments occur at depth in the region.

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

Dismantling

Yogo Peak, seen from Belt Creek Divide, ca.1900

Gold was found at Yogo Creek in 1866. Gold prospectors found blue stones in the river bed below Yogo Dyke from 1878 onwards, but the "blue pebbles" (blue pebbles) were only recognized as sapphires in 1894. It was discovered that they came from the rocks upstream. The mining of the sapphires began in 1895 when a rancher named Jake Hoover sent a cigar box of stones to an appraiser who gave it to Tiffany & Co. in New York. There she assessed Dr. George Frederick Kunz, the leading American gemologist of his time, as "the finest precious gemstones ever found in the United States" (the choicest gemstones ever found in the United States). Hoover then bought the main vein from a shepherd and later sold it to other investors. From this the "English Mine", which was very profitable from 1899 to 1920, developed. Another company, the American Mine, on the western section of Yogo Dyke, was successively owned by a number of investors but was less profitable and was bought by the owners of the English mine. In 1984, mining began in a third section, the Vortex Mine.

Since most yogos are in igneous rock , rather than in alluvial soap , it is difficult to break them down. High American wages also make mining more expensive. It is estimated that at least 28 million carats (5.6 t) of yogos can still be found in the ground. The Yogo Dyke is the only igneous rock from which sapphires are mined.

Special pieces of jewelry

Several Yogo sapphires are kept in the Smithsonian Institution , Washington, DC. The earliest delivery is recorded in the museum's annual report for June 30, 1899, when LT Chamberlain bequeathed two cut yogos and 21 other sapphires to the Isaac Lea gem and mineral collection. A record holder, a 10.2 carat cut yogo, also belongs to the Smithsonian.

Great Yogo sapphire as head of the Conchita Sapphire Butterfly (2007; currently Smithsonian Institution)

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

A representative of the Smithsonian hired Paula Crevoshay, a goldsmith from Albuquerque, New Mexico , to create a piece of jewelry from these stones. Crevoshay chose a butterfly motif to match the natural beauty of America, to honor her mother's love of butterflies, and to highlight the variety of colors in Montana's sapphires. She named the brooch after her mother Conchita, known as the Sapphire Butterfly Brooch, Conchita Sapphire Butterfly or Montana Butterfly Brooch. Most of the stones are from 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, along with Kane, presented it to Smithsonian's curator, Jeffrey Post, on May 7, 2007.

Design for the Tiffany Iris Brooch

Paulding Farnham (1859–1927) of Tiffany & Co. used Yogos in some pieces of jewelry he designed for the 1900 World's Fair in Paris, where Yogo sapphires received a silver medal for color and luster among all the stones presented. Unpolished Yogo Sapphires received the bronze medal at the 1904 Louisiana Purchase Exposition in St. Louis, Missouri .

Tiffany Iris Brooch

For the World's Fair, Farnham also created a full-size iris-shaped brooch, the Tiffany Iris Brooch, for which he used 120 Yogo sapphires and which he sold on March 17, 1900 for $ 6,906.84. In 1923 the First Lady Florence Harding was given a ring from Montana, which was made of Yogo sapphires and gold from Montana. In 1952, Charles Gadsden, the person in charge of the English Mine, handed honed Yogos over to President Harry Truman , his wife Bess and their daughter Margaret.

Since the mining of Yogos was partly operated by British companies, many Yogos were sold in Europe. Yogos may have been in the personal collections of some members of the English royal family in the 1910s, but claims that yogos are part of the English crown jewels cannot be substantiated or refuted.

Sapphires from Montana

Yellow sapphire blank from the Spokane Sapphire Mine near Helena, Montana

The term Yogo sapphire is used for sapphires that come from the Yogo Gulch, while the more general term Montana sapphire (sapphire from Montana) names sapphires that are found elsewhere in Montana. They come in many colors, but yogos are almost always blue. Only a few rubies were found in the Yogo Gulch. Montana produces more sapphire gemstones than any other state in the United States. In 1969 the sapphire and agate were declared Montana's "state gemstone".

literature

  • Stephen M. Voynick: Yogo: the great American sapphire . March 1985 edition. Mountain Press Publishing, Missoula, MT 1985, ISBN 0-87842-217-X .
  • Donald G. Frantz, Norma Jean Russell: Blackfoot Dictionary of Stems, Roots, and Affixes . 2nd Edition. University of Toronto Press, Toronto, ON 2000, ISBN 0-8020-7136-8 .

Web links

Commons : Yogo mine and sapphires  - Collection of images, videos and audio files

Individual evidence

  1. ↑ Descriptions - County Boundaries ( English , PDF; 362 kB) Montana Legislature. P. 22. Retrieved November 5, 2011.
  2. ↑ Montana Highway Map ( English , PDF; 2.9 MB) Montana Natural Resource Information System. Retrieved November 5, 2011.
  3. ^ A b Walter Harvey Weed, Louis Valentine Pirsson: Geology of the Little Belt Mountains, Montana: With Notes on the Mineral Deposits of the Neihart, Barker, Yogo, and Other Districts . United States Geological Survey, United States Government Printing Office , Washington, DC 1900, p. 317-331, 396-400, 447-459, 471, 476, 486, 494, 502-504, 556, 568, 576 ( books.google.com ).
  4. ^ Frantz, Russell: Blackfoot Dictionary of Stems, Roots, and Affixes. 2000, pp. 304, 286, 402.
  5. ↑ Voynick: Yogo: The Great American Sapphire. 1985, pp. 10-11.
  6. ^ A b c d WC McRae, Judy Jewell: Montana . Avalon, Berkeley, CA 2009, ISBN 978-1-59880-014-2 , pp. 339 ( books.google.com ).
  7. ^ Yogo Sapphire Jewelry - Central Montana. (No longer available online.) In: russell.visitmt.com. Montana Russell Country, archived from the original on February 5, 2012 ; Retrieved December 3, 2011 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / russell.visitmt.com
  8. ↑ Voynick: Yogo: The Great American Sapphire. 1985, pp. Ix-xi.
  9. ↑ Peter G. Read: Gemmology . 3. Edition. Elsevier Ltd, Oxford 2005, ISBN 0-7506-6449-5 , pp. 49-51 ( online ).
  10. ↑ a b c d Corundum main page. Department of Geological Sciences, University of Texas at Austin, 1998, accessed October 28, 2011 .
  11. ↑ Voynick: Yogo: The Great American Sapphire. 1985, pp. 6-8.
  12. ↑ a b c d e f g Richard I. Gibson: Yogos: Montana's 'Goldilocks' Gem . In: Star Ridge Publishing LLC (Ed.): Distinctly Montana . , Bozeman, MTSummer 2011. Retrieved October 29, 2011.
  13. ↑ a b c d e Robert E. Kane: The Sapphires of Montana - A Rainbow of Colors . In: Gem World International (ed.): Gem Market News . 22, No. 1, Glenview, IL, January / February 2003, pp. 1-8. "Revised January 2004"
  14. ^ A b Guylaine Gauthier: Mineralogy, geochemistry, and geochronology of the Yogo Dike sapphire deposit, Montana. University of British Columbia, 1995, accessed June 4, 2012 .
  15. ↑ Corundum, Rubies, Sapphire ( English ) In: Gemstones Guide . CIRCA. Retrieved June 4, 2012.
  16. ↑ Voynick: Yogo: The Great American Sapphire. 1985, pp. 151-158.
  17. ↑ Voynick: Yogo: The Great American Sapphire. 1985, pp. 62-63.
  18. ↑ Jane R. Ward, Nancy L Attaway: Yogo Sapphires ( English ) Attaway Gems. Retrieved December 5, 2011.
  19. ^ A b Richard W. Hughes: Gems: Their Sources, Descriptions and Identification . 6th edition. Butterworth-Heinemann, Oxford 2006, ISBN 0-7506-5856-8 , pp. 123, 144-146 ( books.google.com ).
  20. ↑ George F. Kunz: Article 44: On the Sapphires From Montana, with special reference to those from Yogo Gulch in Fergus County . In: Yale University Department of Geology and Geophysics (Ed.): American Journal of Science . 4, No. 24, New Haven, CT, December 1897, pp. 417-420. doi : 10.2475 / ajs.s4-4.24.417 . Retrieved October 29, 2011.
  21. ↑ JH Pratt: Article 46: On the crystallography of the Montana Sapphires . In: Yale University Department of Geology and Geophysics (Ed.): American Journal of Science . 4, No. 24, New Haven, CT, 1897, pp. 424-428. doi : 10.2475 / ajs.s4-4.24.424 .
  22. ↑ a b c Sapphires ( English ) United States Geological Survey. Retrieved October 26, 2011.
  23. ↑ Voynick: Yogo: The Great American Sapphire. 1985, p. 204.
  24. ↑ a b c d e Stephen S. Harlan: Timing of Emplacement of the Sapphire-Bearing Yogo Dike, Little Belt Mountains, Montana Archived from the original on September 5, 2006. (PDF) In: Society of Economic Geologists via George Mason University Academic Research System (Ed.): Economic Geology . 91, No. 6, Littleton, CO, 1996, pp. 1159-1162. doi : 10.2113 / gsecongeo.91.6.1159 . Retrieved December 17, 2011.
  25. ^ A b Henry OA Meyer, Roger H. Mitchell: Sapphire-Bearing Ultramafic Lamprophyre from Yogo, Montana: A Ouachitite . (PDF) In: Mineralogical Association of Canada (Ed.): Canadian Mineralogist . 26, Vancouver, BC, 1988, pp. 81-88. Retrieved December 19, 2011.
  26. ↑ a b L. V. Pirsson: Article 45: On the Corundum-bearing Rock From Yogo Gulch, Montana . In: Yale University Department of Geology and Geophysics (Ed.): American Journal of Science . 4, No. 24, New Haven, CT, 1897, pp. 421-423. doi : 10.2475 / ajs.s4-4.24.421 . Retrieved October 29, 2011.
  27. ↑ Voynick: Yogo: The Great American Sapphire. 1985, pp. 3-4.
  28. ↑ Voynick: Yogo: The Great American Sapphire. 1985, pp. 29-31.
  29. ↑ Voynick: Yogo: The Great American Sapphire. 1985, pp. Viii, 2-3.
  30. ^ DB Sterrett: Mineral Resources of the United States, Calendar Year 1907, Part II Non-Metallic Products . United States Geological Survey, Government Printing Office, Washington, DC 1908, p. 816-819 ( books.google.com ).
  31. ↑ Board of Regents (ed.): Annual Report of the Board of Regents of the Smithsonian Institution for the Year Ending June 30, 1899 . Government Printing Office, Washington, DC 1901, p. 32 ( books.google.com ).
  32. ↑ a b Voynick: Yogo: The Great American Sapphire. 1985, p. 204.
  33. ↑ Sapphire Butterfly Brooch ( English ) Smithsonian Institution. Retrieved November 13, 2011.
  34. ↑ a b Paula Crevoshay: Conchita - Inspiration and Process ( English ) Crevoshay. February 2007. Retrieved November 13, 2011.
  35. ↑ a b Conchita Sapphire Butterfly ( English ) Smithsonian Institution. Retrieved April 21, 2012.
  36. ↑ Crevoshay, Kane Present Sapphire Treasure to Smithsonian ( English , PDF; 1.0 MB) Libertine Jewelry. May 7, 2007. Retrieved November 13, 2011.
  37. ↑ Janet Zapata: The Rediscovery of Paulding Farnham, Tiffany's Designer Extraordinaire, Part I: Jewelry . In: Brant Publications (ed.): Antiques . 139, No. 3, New York, March 1991, p. 561.
  38. ↑ Voynick: Yogo: The Great American Sapphire. 1985, pp. 57-58.
  39. ↑ Voynick: Yogo: The Great American Sapphire. 1985, p. 93.
  40. ↑ Voynick: Yogo: The Great American Sapphire. 1985, pp. 114-115, 204.
  41. ^ William R. Johnston: William and Henry Walters: The Reticent Collectors . Walters Art Gallery, Baltimore, MD 1999, ISBN 0-8018-6040-7 , pp. 271 ( books.google.com ).
  42. ↑ a b State Gemstones Sapphire and Agate ( English ) Montana Office of Tourism. Retrieved November 6, 2011.
  43. ↑ Robert Feldman: Rockhounding Montana . 2nd Edition. Morris Book Publishing, Kearney, NE 2006, ISBN 0-7627-3682-8 , pp. 8 ( books.google.com ).
  44. ^ State gemstones, Montana Code Annotated section 1-1-505 ( English ) Montana Legislative Services. Archived from the original on October 7, 2012. Retrieved November 9, 2011.