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==Mineralogy and geology==
==Mineralogy and geology==
Most sapphires found at Yogo Gulch must be mined from hard [[igneous rock]] rather than from alluvial [[placer deposit]]s. This, plus American labor costs, makes their extraction fairly expensive.{{r|utex}}{{r|pirsson}}{{r|dono}} About $25 million of gemstone has been recovered by all mines at Yogo to date.{{r|utex}}{{r|kane}} However, at least 28 million carats are estimated to still be in the ground.{{r|utex}}{{r|usgs1908}}

Sapphires are a form of [[corundum]], which is crystalline [[aluminium oxide]] and its chemical formula is Al<sub>2</sub>O<sub>3</sub>.<ref name=voynickmineral>{{harvnb|Voynick|1985|pp=ix–xi}}</ref> Corundum is one of the hardest minerals, rating 9 on the [[Mohs scale of mineral hardness|Mohs scale]].{{r|trigon}} Almost all colors of corundum are called [[sapphire]]s, except those of red corundum, which are called [[ruby|rubies]].{{r|utex}} The term "Yogo sapphire" refers only to sapphires from the Yogo Gulch.<ref name=voynickcollins/> The unique cornflower blue color of the Yogo is provided by trace amounts of [[iron]] and [[titanium]].{{r|bluesky}}
Sapphires are a form of [[corundum]], which is crystalline [[aluminium oxide]] and its chemical formula is Al<sub>2</sub>O<sub>3</sub>.<ref name=voynickmineral>{{harvnb|Voynick|1985|pp=ix–xi}}</ref> Corundum is one of the hardest minerals, rating 9 on the [[Mohs scale of mineral hardness|Mohs scale]].{{r|trigon}} Almost all colors of corundum are called [[sapphire]]s, except those of red corundum, which are called [[ruby|rubies]].{{r|utex}} The term "Yogo sapphire" refers only to sapphires from the Yogo Gulch.<ref name=voynickcollins/> The unique cornflower blue color of the Yogo is provided by trace amounts of [[iron]] and [[titanium]].{{r|bluesky}}


Line 59: Line 57:
The [[United States Geological Survey]]{{r|usgs}} and many gem experts<ref name=voynickdep>{{harvnb|Voynick|1985|p=193}}</ref><ref name=voynickfine>{{harvnb|Voynick|1985|p=vii}}</ref> consider them among the world's finest sapphires. However, Yogo roughs tend to be small and flat, so cut Yogo gems heavier than two carats are rare.{{r|usgs}} Only about 10% of cut pieces are over one carat.{{r|kane}} The largest recorded Yogo rough, found in 1910, weighed 19 carats and was cut into an 8-carat gem.{{r|distinctly}} The largest cut Yogo is a 10.2-carat gem held by the Smithsonian Institution.{{r|bluesky}}{{r|distinctly}}<ref name=voynickbig>{{harvnb|Voynick|1985|p=204}}</ref> Yogos tend to be beautiful, small, and very expensive. Because of the rarity of large rough Yogo sapphires, prices for gems begin rising sharply when they are over a half carat, and skyrocket when they are over one carat.{{r|dono}}{{r|distinctly}}{{r|ethics}} About 2% of Yogos are in colors other than blue: almost always purple, and very rarely reddish.{{r|kane}} Sapphires found in the other parts of Montana come in a variety of colors, though rubies are rare.{{r|utex}}{{r|kane}}{{r|kunzgf}} In contrast to traditional Montana sapphires, Yogo sapphires are almost always blue, possibly because their host rock had a longer cooling time, allowing the trace titanium and iron to be evenly distributed in the sapphire crystals throughout the intrusive body.{{r|distinctly}}
The [[United States Geological Survey]]{{r|usgs}} and many gem experts<ref name=voynickdep>{{harvnb|Voynick|1985|p=193}}</ref><ref name=voynickfine>{{harvnb|Voynick|1985|p=vii}}</ref> consider them among the world's finest sapphires. However, Yogo roughs tend to be small and flat, so cut Yogo gems heavier than two carats are rare.{{r|usgs}} Only about 10% of cut pieces are over one carat.{{r|kane}} The largest recorded Yogo rough, found in 1910, weighed 19 carats and was cut into an 8-carat gem.{{r|distinctly}} The largest cut Yogo is a 10.2-carat gem held by the Smithsonian Institution.{{r|bluesky}}{{r|distinctly}}<ref name=voynickbig>{{harvnb|Voynick|1985|p=204}}</ref> Yogos tend to be beautiful, small, and very expensive. Because of the rarity of large rough Yogo sapphires, prices for gems begin rising sharply when they are over a half carat, and skyrocket when they are over one carat.{{r|dono}}{{r|distinctly}}{{r|ethics}} About 2% of Yogos are in colors other than blue: almost always purple, and very rarely reddish.{{r|kane}} Sapphires found in the other parts of Montana come in a variety of colors, though rubies are rare.{{r|utex}}{{r|kane}}{{r|kunzgf}} In contrast to traditional Montana sapphires, Yogo sapphires are almost always blue, possibly because their host rock had a longer cooling time, allowing the trace titanium and iron to be evenly distributed in the sapphire crystals throughout the intrusive body.{{r|distinctly}}


⚫
The Yogo sapphires were first discovered in [[alluvium]] during gold mining operations, but later traced to their source within the dike.{{r|Harlan}} Except for the Yogo Gulch deposit and one small site in [[Kashmir]], most other corundum is alluvial; mined from the sand and gravel created by the weathering of [[metamorphic rock]]. Alluvial sapphires are found in the Orient, Australia, and in three other Montana locations—the [[Missouri River]], [[Rock Creek (Montana)|Rock Creek]], and [[Dry Cottonwood Creek (Deer Lodge County, Montana)|Dry Cottonwood Creek]].<ref name=voynickdep/>{{r|gemgallerymtloc}} The location of most Yogo sapphires within hard [[igneous rock]] rather than from alluvial [[placer deposit]]s, coupled with American labor costs, makes their extraction fairly expensive.{{r|utex}}{{r|pirsson}}{{r|dono}} About $25 million of gemstone has been recovered by all mines at Yogo to date.{{r|utex}}{{r|kane}} However, at least 28 million carats are estimated to still be in the ground.{{r|utex}}{{r|usgs1908}}
⚫
The host rock for the sapphires, the Yogo [[Dike (geology)|dike]], is a dark gray to green [[lamprophyre]] which consists of [[clinopyroxene]] and [[phlogopite]] [[phenocryst]]s set in a [[Matrix (geology)|matrix]] of clinopyroxene, titanian magnetite, [[apatite]], [[Chlorite group|chlorite]], [[Serpentine group|serpentine]] and [[calcite]]. The phlogopite composition suggests a 900&nbsp;°C crystallization temperature. [[Xenolith]]s of limestone, [[clastic]] [[sedimentary rock]]s, and [[gneiss]] are present. In some locations, due to the abundance of xenoliths, the dike has the appearance of a limestone [[breccia]] in an igneous matrix.{{r|Harlan}}

One gneiss fragment found as a xenolith within the dike contains corundum. The Yogo sapphires themselves are rimmed with a reaction layer of [[spinel]] and are etched, indicating that the sapphires were not in chemical equilibrium with their host, the lamprophyre magma. This suggests the sapphire crystals may have originated in an earlier rock, such as a corundum bearing gneiss, assimilated by the lamprophyre magma at depth.{{r|Harlan}}{{r|Meyer}} Earlier investigators had assumed that the sapphire had crystallized from the magma with the necessary high aluminium content provided by assimilation of clay rich [[shale]]s of the [[Proterozoic]] [[Belt Supergroup]] sediments which are known to be present at depth in the region.{{r|kunzgf}}

The Yogo dike has a near vertical [[Strike and dip|dip, and a strike]] (compass orientation) of 75° east of north and contains three ''en echelon'' segments. The dike varies from {{convert|2|to|26|ft|m}} thick and extends for some {{convert|5|mi|km|abbr=on}} along the strike.{{r|Harlan}} The dike has been dated at 48.6 [[Mya (unit)#Symbols y and yr|mya]] using [[Argon–argon dating|Ar dating]] on phlogopite. The dike intrudes [[Mississippian|Mississippian age]] (360 to 325 Mya) limestone and other sedimentary rocks of the [[Madison Group|Madison]] and [[Big Snowy Group]]s.{{r|Harlan}}


⚫
The host rock for the sapphires, the Yogo [[Dike (geology)|dike]], is a dark gray to green [[lamprophyre]] which consists of [[clinopyroxene]] and [[phlogopite]] [[phenocryst]]s set in a [[Matrix (geology)|matrix]] of clinopyroxene, titanian magnetite, [[apatite]], [[Chlorite group|chlorite]], [[Serpentine group|serpentine]] and [[calcite]]. The phlogopite composition suggests a 900&nbsp;°C crystallization temperature. [[Xenolith]]s of limestone, [[clastic]] [[sedimentary rock]]s, and [[gneiss]] are present. In some locations, due to the abundance of xenoliths, the dike has the appearance of a limestone [[breccia]] in an igneous matrix.{{r|Harlan}} One gneiss fragment found as a xenolith within the dike contains corundum. The Yogo sapphires themselves are rimmed with a reaction layer of [[spinel]] and are etched, indicating that the sapphires were not in chemical equilibrium with their host, the lamprophyre magma. This suggests the sapphire crystals may have originated in an earlier rock, such as a corundum bearing gneiss, assimilated by the lamprophyre magma at depth.{{r|Harlan}}{{r|Meyer}} Earlier investigators had assumed that the sapphire had crystallized from the magma with the necessary high aluminium content provided by assimilation of clay rich [[shale]]s of the [[Proterozoic]] [[Belt Supergroup]] sediments which are known to be present at depth in the region.{{r|kunzgf}}
⚫
The Yogo sapphires were first discovered in [[alluvium]] during gold mining operations, but later traced to their source within the dike.{{r|Harlan}} Except for the Yogo Gulch deposit and one small site in [[Kashmir]], most other corundum is alluvial; mined from the sand and gravel created by the weathering of [[metamorphic rock]]. Alluvial sapphires are found in the Orient, Australia, and in three other Montana locations—the [[Missouri River]], [[Rock Creek (Montana)|Rock Creek]], and [[Dry Cottonwood Creek (Deer Lodge County, Montana)|Dry Cottonwood Creek]].<ref name=voynickdep/>{{r|gemgallerymtloc}}


There had been considerable debate over the years about how deep the Yogo dike was and how many ounces of rough sapphires per ton it contained, or "ounces per ton". In the late 1970s and early 1980s Delmer L. Brown, a geological engineer and gemologist, conducted the most thorough scientific exploration of the dike to date and showed it was at least {{convert|7000|ft|m}} deep and that the amount of rough sapphires was not consistent throughout the deposit.<ref name=voynickbrown>{{harvnb|Voynick|1985|pp=151–158}}</ref> He determined that the dike's erosion was minimal and recent. Brown also showed that the unique characteristics of the Yogo sapphires are related to their geological history. Most sapphires are formed under low pressure and temperature over geologically short periods of time, and this is why most non-Yogo sapphires have imperfections and inconsistent coloring.<ref name=voynickbrown/> Yogos show crystalline formation over very high temperatures and pressures over geologically long periods of time. These conditions are only possible at great depth. Yogos were formed at great depths, at least thousands of feet, perhaps miles deep, and then carried upwards by slowly thickening magma. As sapphires are heavier then magma, the smaller roughs rose closer to the surface,<ref name=voynickbrown/> causing the Yogo sapphires to be generally small, which was later confirmed by subsequent mining at the English Mine. Brown also showed that distribution of gem rough through the dike was not consistent, so using an average "ounces per ton" was misleading. What came to be known as the American Mine was built at a part of the dike with significantly lower "ounces per ton" than the English Mine. As a result of Brown's findings, operations at the American Mine were permanently shut down.<ref name=voynickbrown/>
The Yogo dike has a near vertical [[Strike and dip|dip, and a strike]] (compass orientation) of 75° east of north and contains three ''en echelon'' segments. The dike varies from {{convert|2|to|26|ft|m}} thick and extends for some {{convert|5|mi|km|abbr=on}} along the strike.{{r|Harlan}} The dike has been dated at 48.6 [[Mya (unit)#Symbols y and yr|mya]] using [[Argon–argon dating|Ar dating]] on phlogopite. The dike intrudes [[Mississippian|Mississippian age]] (360 to 325 Mya) limestone and other sedimentary rocks of the [[Madison Group|Madison]] and [[Big Snowy Group]]s.{{r|Harlan}} There had been considerable debate over the years about how deep the Yogo dike was and how many ounces of rough sapphires per ton it contained, or "ounces per ton". In the late 1970s and early 1980s Delmer L. Brown, a geological engineer and gemologist, conducted the most thorough scientific exploration of the dike to date and showed it was at least {{convert|7000|ft|m}} deep and that the amount of rough sapphires was not consistent throughout the deposit.<ref name=voynickbrown>{{harvnb|Voynick|1985|pp=151–158}}</ref> He determined that the dike's erosion was minimal and recent. Brown also showed that the unique characteristics of the Yogo sapphires are related to their geological history. Most sapphires are formed under low pressure and temperature over geologically short periods of time, and this is why most non-Yogo sapphires have imperfections and inconsistent coloring.<ref name=voynickbrown/> Yogos show crystalline formation over very high temperatures and pressures over geologically long periods of time. These conditions are only possible at great depth. Yogos were formed at great depths, at least thousands of feet, perhaps miles deep, and then carried upwards by slowly thickening magma. As sapphires are heavier then magma, the smaller roughs rose closer to the surface,<ref name=voynickbrown/> causing the Yogo sapphires to be generally small, which was later confirmed by subsequent mining at the English Mine. Brown also showed that distribution of gem rough through the dike was not consistent, so using an average "ounces per ton" was misleading. What came to be known as the American Mine was built at a part of the dike with significantly lower "ounces per ton" than the English Mine. As a result of Brown's findings, operations at the American Mine were permanently shut down.<ref name=voynickbrown/>


==Montana sapphires==
==Montana sapphires==

Revision as of 12:55, 31 December 2011

Yogo sapphire
A 0.43 carat pear-shaped cornflower blue Yogo sapphire
A 0.43 carat pear-shaped cornflower blue Yogo sapphire
General
CategoryOxide mineral
Formula
(repeating unit)		Aluminium oxide, Al2O3
Crystal systemHexagonal
Symbol (32/m)
Space group R3c
Identification
ColorCornflower blue to purple
Crystal habitHexagonal, rhombohedral, prismatic or dipyramidal
TwinningLamellar
CleavagePartings on {0001} and {1011}
FractureUneven to conchoidal
TenacityBrittle
Mohs scale hardness9.0
LusterAdamantine to vitreous
Specific gravity3.98–4.10
Optical propertiesUniaxial (–) Abbe number 72.2
Refractive indexnω=1.767–1.772
nε=1.759–1.763,
Birefringence 0.008
PleochroismWeak
2V angle58°
References[1]

Yogo sapphires are a special cornflower blue color variety of corundum found only in Yogo Gulch, Judith Basin County, Montana, United States. Gemologists consider then among the finest sapphires in the world. The word Yogo means "romance or blue sky" in the Piegan Blackfeet language. They were discovered at Yogo Gulch in 1865 and sapphire mining began there in 1895. About $25 million in gemstone has been recovered from all of the mines at Yogo, and at least 28 million carats are estimated to still be in the ground.

The cornflower blue color of the Yogo results from trace amounts of iron and titanium. Although Yogo sapphires are rarer than diamonds, their quality and value were not immediately evident to those that discovered them. Due to the unique nature of the dike that Yogo sapphires are found in, mining efforts at Yogo Gulch have been sporadic and rarely profitable. In 1969 the sapphire and Montana agate were designated the Montana state gemstones. Yogo sapphires are included in the Smithsonian Institution's gem collection.

Location

Judith Basin County, where Yogo Gulch is located

Yogo sapphires are mined in a region historically inhabited by the Piegan Blackfeet people. In the Piegan Blackfeet language, the word Yogo means "romance, blue sky", although there is some debate about this.[2][3] The true meaning had already been lost by 1878 when placer gold was found in Yogo Creek. Other meanings for Yogo have been put forward, including "Going over the hill".[4] Yogo Gulch (46°50′45″N 110°18′38″W / 46.84583°N 110.31056°W / 46.84583; -110.31056 (Yogo Creek))[5] is in Judith Basin County, Montana, located 12 miles (19 km) southwest (SW) of Utica, Montana and 45 miles (72 km) west-southwest (WSW) of Lewistown, Montana. It lies east of Great Falls, Montana.[6][7][8] Judith Basin County was broken out from western Fergus County, Montana and eastern Cascade County, Montana on December 10, 1920. At the time of discovery, this area was part of Fergus County, Montana.[9][10] Yogo Peak (8,625 feet (2,629 m)), Yogo Creek, Yogo Gulch, and the Yogo dike are located in the portion of the Little Belt Mountains that lies within Judith Basin County.[8]

The Judith River flows northeast out of the Little Belts towards Utica. East of the river is Pig-Eye Basin—where Jake Hoover, claimed to be the discoverer of Yogo sapphires, had a ranch. Yogo Gulch lies to the west of the river. Yogo Peak is about 15 miles (24 km) west of the Judith River. Yogo Creek originates there and flows southeast to its confluence with the Middle Fork of the Judith River a few miles upstream of where the Middle Fork joins the Judith. Yogo Gulch is located along the lower reaches of Yogo Creek, and the Yogo dike originates a few miles north of the stream's confluence, then runs from west-southwest to east-northeast from Yogo Creek to just before the Judith River.[11]

Mineralogy and geology

Sapphires are a form of corundum, which is crystalline aluminium oxide and its chemical formula is Al2O3.[12] Corundum is one of the hardest minerals, rating 9 on the Mohs scale.[13] Almost all colors of corundum are called sapphires, except those of red corundum, which are called rubies.[14] The term "Yogo sapphire" refers only to sapphires from the Yogo Gulch.[15] The unique cornflower blue color of the Yogo is provided by trace amounts of iron and titanium.[2]

Yogo sapphires are unique among the world's sapphires: they lack color zoning, are free of cavities, do not need heat treating because their cornflower blue coloring is uniform and deep, are generally free of inclusions, and have high uniform clarity.[16] Unlike Asian sapphires, they maintain their brilliance in artificial light.[17] Since they are found as primary constituent minerals within an igneous bedrock rather than in sedimentary alluvial deposits where most other sapphires are located,[16] Yogos present an advantage to gemcutters: they retain a perfect or near-perfect crystalline shape, making the work of gem-cutting much easier, as does their lack of inclusions, color zoning, or cloudiness.[18] Yogos also have a trigon pattern,[13] with rhombohedral crystals, a feature which is absent from sapphires from other parts of Montana.[19][20] These rhombohedrons are almost always less than 1 mm in thickness and appear like striations.[21]

A 0.19 carat diamond-cut cornflower blue Yogo sapphire.
A 0.37 carat brilliant-cut purple Yogo sapphire. Only about 2% of Yogo sapphires are purple.

The United States Geological Survey[22] and many gem experts[23][24] consider them among the world's finest sapphires. However, Yogo roughs tend to be small and flat, so cut Yogo gems heavier than two carats are rare.[22] Only about 10% of cut pieces are over one carat.[16] The largest recorded Yogo rough, found in 1910, weighed 19 carats and was cut into an 8-carat gem.[25] The largest cut Yogo is a 10.2-carat gem held by the Smithsonian Institution.[2][25][26] Yogos tend to be beautiful, small, and very expensive. Because of the rarity of large rough Yogo sapphires, prices for gems begin rising sharply when they are over a half carat, and skyrocket when they are over one carat.[19][25][27] About 2% of Yogos are in colors other than blue: almost always purple, and very rarely reddish.[16] Sapphires found in the other parts of Montana come in a variety of colors, though rubies are rare.[14][16][20] In contrast to traditional Montana sapphires, Yogo sapphires are almost always blue, possibly because their host rock had a longer cooling time, allowing the trace titanium and iron to be evenly distributed in the sapphire crystals throughout the intrusive body.[25]

The Yogo sapphires were first discovered in alluvium during gold mining operations, but later traced to their source within the dike.[28] Except for the Yogo Gulch deposit and one small site in Kashmir, most other corundum is alluvial; mined from the sand and gravel created by the weathering of metamorphic rock. Alluvial sapphires are found in the Orient, Australia, and in three other Montana locations—the Missouri River, Rock Creek, and Dry Cottonwood Creek.[23][29] The location of most Yogo sapphires within hard igneous rock rather than from alluvial placer deposits, coupled with American labor costs, makes their extraction fairly expensive.[14][30][19] About $25 million of gemstone has been recovered by all mines at Yogo to date.[14][16] However, at least 28 million carats are estimated to still be in the ground.[14][31]

The host rock for the sapphires, the Yogo dike, is a dark gray to green lamprophyre which consists of clinopyroxene and phlogopite phenocrysts set in a matrix of clinopyroxene, titanian magnetite, apatite, chlorite, serpentine and calcite. The phlogopite composition suggests a 900 °C crystallization temperature. Xenoliths of limestone, clastic sedimentary rocks, and gneiss are present. In some locations, due to the abundance of xenoliths, the dike has the appearance of a limestone breccia in an igneous matrix.[28] One gneiss fragment found as a xenolith within the dike contains corundum. The Yogo sapphires themselves are rimmed with a reaction layer of spinel and are etched, indicating that the sapphires were not in chemical equilibrium with their host, the lamprophyre magma. This suggests the sapphire crystals may have originated in an earlier rock, such as a corundum bearing gneiss, assimilated by the lamprophyre magma at depth.[28][32] Earlier investigators had assumed that the sapphire had crystallized from the magma with the necessary high aluminium content provided by assimilation of clay rich shales of the Proterozoic Belt Supergroup sediments which are known to be present at depth in the region.[20]

The Yogo dike has a near vertical dip, and a strike (compass orientation) of 75° east of north and contains three en echelon segments. The dike varies from 2 to 26 feet (0.61 to 7.92 m) thick and extends for some 5 mi (8.0 km) along the strike.[28] The dike has been dated at 48.6 mya using Ar dating on phlogopite. The dike intrudes Mississippian age (360 to 325 Mya) limestone and other sedimentary rocks of the Madison and Big Snowy Groups.[28] There had been considerable debate over the years about how deep the Yogo dike was and how many ounces of rough sapphires per ton it contained, or "ounces per ton". In the late 1970s and early 1980s Delmer L. Brown, a geological engineer and gemologist, conducted the most thorough scientific exploration of the dike to date and showed it was at least 7,000 feet (2,100 m) deep and that the amount of rough sapphires was not consistent throughout the deposit.[33] He determined that the dike's erosion was minimal and recent. Brown also showed that the unique characteristics of the Yogo sapphires are related to their geological history. Most sapphires are formed under low pressure and temperature over geologically short periods of time, and this is why most non-Yogo sapphires have imperfections and inconsistent coloring.[33] Yogos show crystalline formation over very high temperatures and pressures over geologically long periods of time. These conditions are only possible at great depth. Yogos were formed at great depths, at least thousands of feet, perhaps miles deep, and then carried upwards by slowly thickening magma. As sapphires are heavier then magma, the smaller roughs rose closer to the surface,[33] causing the Yogo sapphires to be generally small, which was later confirmed by subsequent mining at the English Mine. Brown also showed that distribution of gem rough through the dike was not consistent, so using an average "ounces per ton" was misleading. What came to be known as the American Mine was built at a part of the dike with significantly lower "ounces per ton" than the English Mine. As a result of Brown's findings, operations at the American Mine were permanently shut down.[33]

Montana sapphires

An uncut/rough yellow sapphire found at the Spokane Sapphire Mine near Helena, Montana

The term "Montana sapphire" generally refers to gems from Montana locations other than Yogo Gulch, where "Yogo sapphires" is the preferred term.[16] More gem-quality sapphires are produced in Montana than anywhere else in North America.[16] These gems inspired the names of geologic features; the mountains near Rock Creek are known as the Sapphire Mountains. Garnets are also found at some Montana sapphire sites, inspiring the name of the Garnet Range, which lies to the north of the Sapphire Mountains.[34]

The first Sapphires found in the United States were discovered on May 5, 1865 along the Missouri River about 14 miles east of Helena, Montana in Lewis and Clark County, Montana by Ed "Sapphire" Collins.[16][15] Although Collins sent his find to Tiffany's in New York City and Amsterdam for evaluation, the sapphires he sent had poor coloring and overall quality, so they garnered little notice and initially gave Montana sapphires a poor reputation.[35] Corundum was also found at Dry Cottonwood Creek near Butte in 1889, Rock Creek near Philipsburg in 1892, and Quartz Gulch near Bozeman in 1894.[16][36][37] By 1890, the British-owned Sapphire and Ruby Mining Company had bought several thousand acres of land where Montana sapphires were found, but the venture failed after a few years due to fraud perpetrated by the owners.[38]

Sapphires from these three sites are routinely heat treated to enhance color.[16] While millions of carats of sapphires have been mined from the Missouri River deposits, there has been little activity there since the 1990s due to recovery costs and environmental concerns, though small scale "pan-your-own" operations allowing individuals to prospect for sapphires remain in operation. Production at Dry Cottonwood Creek has been sporadic and low-yielding. The Rock Creek area, also known as Gem Mountain, has been the most productive site in Montana by far, even more so than Yogo Gulch, producing over 190 million carats of sapphires.[16]

History

File:JakeHoover1894.png
Jake Hoover at age 45 in 1894. Photo taken in Lewistown for his wedding.

Mining production of Yogos has proven difficult and sporadic over the years. Although gold had first been discovered at Yogo Creek in 1866, the early prospectors were chased off by local Native Americans.[4][39] During the Montana Gold Rush of 1878, about one thousand men came to Yogo Creek as a result of a gold strike; Yogo Creek being one of the gold-bearing streams in Montana that had not been actively mined. The mining camp of Yogo City flourished for about three years, but only bits of gold and "blue pebbles" were found.[4] Thus, the population dwindled until only a few people were left.[4]

While on a weight-for-weight basis sapphires are worth more than gold, and the Yogo mines ultimately produced more dollar value than several gold strikes, production of Yogos required hard rock mining and sophisticated marketing, whereas gold was easier to identify and merely required digging and selling.[40] Nonetheless, sapphire mining at Yogo Gulch began when someone finally thought to investigate the nature of the "blue pebbles" which had been found in 1894 within the alluvium during gold mining.[17][28] In 1895, Jake Hoover sent a cigar box containing those he had collected while mining gold to an assay office, which in turn sent them via regular, uninsured mail to Tiffany's in New York City for appraisal by gemologist Dr. George Frederick Kunz,[16] the leading American gemologist of the time.[41] Impressed by their quality and color, Kunz pronounced them “the finest precious gemstones ever found in the United States".[42] Tiffany's sent Hoover a check for $3,750 along with a letter that described the blue pebbles as “sapphires of unusual quality.” Yogos were ultimately traced from the alluvium to their source within the dike.[28] In February 1896, sheepherder Jim Ettien found the sapphire mother lode, the Yogo dike, while following a line of gopher holes. He sold it to Hoover.[13][43][44] Hoover in turn sold his interest in his eight original mining stakes, known as the "New Mine Sapphire Syndicate," to his two partners for $5,000.[31] For several years prior to discovering Yogo sapphires, Hoover had a ranch in Pig-Eye Basin. Afterwards he prospected for gold in Alaska and was a deep-sea fishing guide in Seattle, before eventually returning to the Judith Basin.[39][45]

1900s-1930s

On July 4, 1896, two other Americans, John Burke and Pat Sweeney, staked mining claims at six sections of western portion of the Yogo dike: areas Hoover had deemed unfit for mining. These claims were known as the "Fourth of July Claim". This mine became known as the "American Mine", bought in 1904 by the American Gem Syndicate and purchased in 1907 by the American Sapphire Company.[46]

A prominent long-term local resident was Millie Ringold, a former slave born in 1845. She had settled in Fort Benton, Montana after having worked as a nurse and servant for an army general. Millie promptly left for the Yogo gold fields, selling her boarding house in Fort Benton and setting up a hotel, restaurant, and saloon. She also sang and played music.[47] Millie became known as a superb cook at the English Mine, but by 1903 she had fallen on hard times. She remained there until she died in 1906, was considered Yogo City's most prominent citizen, and ultimately the last resident of the city.[47][48] Yogo City also was briefly known as Hoover City,[49] after Jake Hoover, who employed and remained lifelong friends with western painter Charles Marion Russell.[50] Russell stated he learned most of his frontier skills from Hoover.[36][51] The nearby town of Utica was featured in Russell's 1907 painting A Quiet Day in Utica,[52][53] which was originally known as Tinning a Dog. Russell himself, Hoover, and Ringold are all depicted in the painting.[54][55]

Miners cleaning a sluice box in Yogo Gulch.

In 1899, gem merchants Johnson, Walker and Tolhurst, Ltd. of London paid $100,000 for the New Mine Sapphire Syndicate, which then became unofficially known as the "English Mine."[56] This site was 5 miles (8.0 km) from Yogo City. One of the Englishmen who came to the area was Charles Gadsden of Berkhamsted. By 1900, there was little left of the gold mine, though Ringold was still working gold claims. By 1902, Gadsden was promoted to resident supervisor of the English Mine and he quickly turned the mine's focus to sapphires.[57] Weight-for-weight rough sapphires are worth much more than gold, and Gadsden's security measures were very tight.[58] The English Mine flourished until the 1920s.[43][56] Floods so severely damaged the mines on July 26, 1923 that they never fully recovered.[17] The "English Mine" finally succumbed to the aftermath of the floods and hard economic times in 1929.[59] It had recovered more than 16 million carats of rough sapphires that were valued at $2.5 million. Subsequently a series of several other firms mined the sapphires but with marginal success.[39][43][56] For much of the 1930s and 1940s Gadsden was the sole employee of the mine and spent $29,000 of his own money to pay the mine's property taxes.[60]

Operations at the English Mine were significantly more profitable than at the American Mine, largely because of the mining and management techniques employed, insufficient space and water for ore weathering at their end of the Yogo dike, and inability to market the gems within the United States. Roughs from the English Mine were shipped to London and sold in Europe, often as sapphires from the Far East. The American Sapphire Company, which used less skilled gemcutters from Great Falls, Montana, went bankrupt in 1909 and a new firm, the Yogo American Sapphire Company bought the American Mine but went bankrupt in 1913. The American Mine was then bought by New Mine Sapphire Syndicate in 1914, which quickly recouped its purchase price by washing the tailings left behind by the American Mine.[61][62] Sapphire mining at the other Montana sapphire mines was even less successful because of the very low profit margin in sapphires that are not blue. Blue sapphires are extremely rare at Montana sites other than Yogo Gulch.[39][63]

1940s-1970s

Millie Ringold, circa 1900. The structure in the background is a waterwheel that was used to power a crusher at Yogo City's Weatherwax Mine.

Other Montana sapphires were heavily mined during World War II for industrial uses. However, because the Yogo mines were still owned by the British, they were little affected by the war. Gadsden remained caretaker of the mines until shortly before his death on March 11, 1954.[64] The sixth American company to acquire the Yogo dike was the Yogo Sapphire Mining Corporation of Billings, Montana. The firm made its initial offer in 1946 and obtained an agreement with the English in 1949. However, legal wrangling delayed the actual purchase until July 1956. The final price was $65,000 and various stock considerations. Similar to the previous Yogo ventures, its capital was exhausted. The Yogo Sapphire Mining Corporation then changed its name to the same as the British firm's name: New Mine Sapphire Syndicate. It became known as the "American Syndicate" to distinguish it from the previous "English Syndicate". Production was poor and mining ceased in September 1959.[65] From 1959–1963 the mine was "open" resulting in hobbyists, picknickers, and rockhounds from all over America and Canada coming to gather loose rough. The American Syndicate finally took action to stop this in 1963, with fences and threats of prosecution.[66] The American Syndicate had leased the mine to several operators. One of these was Siskon, Inc. of Nevada, who lost a significant amount of money. They sued and in May 1965 the Montana Supreme Court ruled in Siskon's favor. Siskon bought the mine at a sheriff's sale and in turn leased it to a group headed by Arnold Baron, who had a background in gemcutting and jewelry. Baron organized German and Thai gemcutters and had success in marketing Yogos in America—the first time that occurred in 50 years. However, due to the difficulty in mining the hard rock site, he did not exercise his option to buy the mine and Siskon sold it in August 1968 when Herman Yaras of Oxnard, California bought it for $585,000.[67]

Yaras' firm was called Sapphire Village, Inc. This eventually led to what is now called Sapphire Village in early 1969, a nearby homesite development where people can gather their own sapphires through limited mining rights. Mining on these homesites was limited to hand tools. Meanwhile, Sapphire Village, Inc. did little to mine and market sapphires and it folded. Yaras sold the mine in 1973 to Chikara Kunisaki, an Oxnard, California native and celery farmer. Kunisaki owned one of the original homes in Sapphire Village and named his firm Sapphire International Corporation. Kunisaki then made the first serious effort to mine Yogo Gulch since the early days of the English Mine. He built a modern 3,000 foot tunnel at the site of the old American Mine that became known as the "Kunisaki Tunnel". However, Sapphire International Corporation's operations were so costly that it shut down operations in fall 1976.[68]

Victor di Suvero and his firm Sapphire-Yogo Mines were next in January 1977 with a lease on the mine. Di Suvero was a native-born Italian who grew up in Tientsin, China and had been successful with a jade mine in California. Di Suvero's expertise was in marketing and he formed Sapphire Trading to cut and market the Yogos. He had novel marketing ideas but neglected the mining aspects of business. Consequently he was unable to make payments and this venture folded in fall 1979. At this point, only 4 Americans had been successful at Yogo Gulch and that was early in its mining history. At least thirteen American Yogo mining efforts had failed. Besides financial and hard rock mining difficulties, the Americans did not understand gem marketing. They generally approached the Yogos as if they were gold nuggets; not being able to see past a bag full of sapphire roughs.[69]

1980s and beyond

The American Mine hoist at Yogo mines.

Kunisaki then put his mine up for sale, asking $6 million to recoup his expenses. Even though mine profits had been poor over the decades, during this time prices of precious gems were very high due to the worldwide oil crises of the 1970s and early 1980s. Four individuals or groups seriously considered Kunisaki's offer.[70] Relying heavily upon the expertise of Brown, Harry C. Bullock and J. R. Edington formed the limited partnership American Yogo Sapphire Limited, the 14th American company to work the Yogo dike. They paid the $6 million price and then raised $7.2 million in funding by October 1981. Bullock and Brown had Yogo mine experience prior to this as they had worked with di Suvero. Bullock's plan included mining, cutting, making jewelry, and marketing—the whole spectrum of the business. Brown discovered quality gemcutters in Thailand who were willing to improve their skills, and accordingly set up the American Yogo Sapphire Company at that location. Brown also set up a security system that was computerized, thorough, and started at the mine and included the Thai cutters.[70] Bigger roughs were sent to American cutters, specialty cuts were done in Germany, and a few cuts were done in Hong Kong. The vast majority of cuts were done in Thailand. American Yogo Sapphire Limited secured a $5 million line of credit with Citibank. Desiring a more modern name, American Yogo Sapphire Limited changed its name to Intergem Limited in spring 1982. Intergem marketed the Yogo as the Royal American Sapphire. Their first line of jewelry appeared in late summer 1982. Intergem started by marketing the jewelry regionally in the American west and then national marketing. They also developed a system of authorized dealers. Intergem began marketing the Yogo, rather Royal American Sapphire, as the world's only guaranteed untreated sapphire—a claim which rocked the gem trade because by 1982 the issue of heat treating gems had become a major issue in the gem trade.[70] At that time 95% of all the world's sapphires were being heated to enhance their natural color. The Thais had taken this a step further by buying large quantities of Sri Lankan sapphires that were naturally colorless, known as geuda, and heating them to a totally artificial blue.[71] Compounding the problem, heated gems often fade over time. Trained gemologists can detect a heated gem with an accuracy of 95%. Intergem's marketing of guaranteed untreated Yogos set them against many in the gem industry. This issue appeared as a front page story in the Wall Street Journal on August 29, 1984 in an article by Bill Richards entitled "Carats and Schticks: Sapphire Marketer Upsets The Gem Industry".[71] In its first 4 years Intergem met with success. In 1984 alone sales were over $3 million. In 1985 there was a movement in Pennsylvania to require disclosure that a gem had been treated. Large numbers of gem professionals were visiting Yogo Gulch. However, problems were brewing.[72]

Gemcutting in Thailand

Intergem had begun planning to dig even deeper into the Yogo dike; which held more known reserves than all the world's other known sapphire deposits combined; albeit deep underground than near the surface like the other known deposits. By this time Sapphire International Corporation had been renamed to Roncor; to which Intergem had made a down payment and agreed to make semi-annual payments. Intergem also had loan and interest payments to make to Citibank. Intergem's sales were steadily increasing, but even still not enough cash was coming in and in May 1985 they missed a $250,000 payment to Roncor. Their collateral with Citibank had declined because their collateral was their own inventory and the value of gems was declining. Citibank called in its loan. Intergem had over $1 million in sales lined up for the 1985 Christmas season but could only fill a tiny portion. In summer 1986 Roncor regained full ownership even though Intergem had sold carats and jewelry worth millions of dollars.[73]

While the various companies attempted mine leasing with Roncor, two local married couples discovered a new site at Yogo Gulch in January 1984 by following a trail to an unused section of the dike that had previously been deemed unsuitable. They began mining the site and named it the "Vortex Mine". The company was named Vortex Mining. The mine shaft went 280 feet (85 m) down and contained two Yogo ore-bearing veins.[74] The mine was successful for years but eventually declined and the Vortex Mine, which was now called Yogo Creek Mining,[16] closed in 2004. The portion of the dike they had mined was an extension of the main dike. In 1992 Roncor found an 11 carat rough.[75]

AMAX Exploration, operating as the Yogo Sapphire Project, signed a 22-month lease with Roncor in March 1993 and had some success in the middle and eastern portions of the dike but decided not to continue after the end of its lease due to the cost of underground mining, depletion of easily accessible Yogos, and the relatively small size of Yogos currently easily accessible. During this time additional dikes were found in the area and low grade rough was found in what is known as the "Eastern Flats Dike".[76]

In 1995 Intergem's stock of gems began to reappear on the market because during its demise Intergem had paid its salesmen in sapphires. After Intergem collapsed, many of its salesmen continued to sell Yogos, especially after AMAX ceased operations. Citibank also had obtained a large stock of Yogo pieces as a result of Intergem's demise reputedly worth $3.5 million and consisting of 200,000 carats of rough, 22,000 carats of cut gems, and 2,000 pieces of jewelry. This sat in the bank's vaults until 1991 when Sofus Michelsen, director of the Center for Gemstone Evaluation and creator of the Michelsen Gemstone Index, became interested. In 1992 he and Jim Adair, a Missoula, Montana jeweler who is the world's largest retailer of Yogos, got together and by October 1994 Adair had purchased Citibank's four sealed bags of Yogo material. However, only one of the bags was truly valuable. Adair and Michelsen designed custom cutting techniques for Yogos.[77] Then a Canadian company called Pacific Cascade Sapphires operated a mining lease from Roncor in 2000 and 2001 but ran out of funds before becoming successful and their option expired. By this time most of the easily accessible Yogos had been mined and miners were having to dig deeper; further increasing costs.[16]

A new owner bought Vortex in 2008 and is in operation as of late 2011. Its operations are environmentally friendly, using methods such as recycling all water and not using other chemicals.[25] As of 2011, there is also mining activity at Sapphire Village, though the Roncor mines are inactive.[22]

State gem of Montana

File:Yogo1ct.jpg
A one-carat Yogo sapphire.

The sapphire became one of Montana's two official state gemstones in 1969, 104 years from the time of discovery. Although "Sapphire" Collins recognized as early as 1865 that pebbles he found the Missouri River were of value, he could not convince bankers, merchants, or gem dealers of this since his finds were of lesser quality. It was the discovery of Yogo sapphires at Yogo Gulch in 1895 that spurred investment in sapphire mines throughout the state, mostly by influential people and firms from the eastern United States and England. In the 20th century, when designation of a state gemstone was considered, the Montana Council of Rock and Mineral Clubs supported two nominees: sapphires and Montana agates. Agates were chosen due to their great abundance, particularly in the Yellowstone River basin, which flows from Yellowstone National Park north to Livingston, then east through Montana until its confluence with the Missouri just over the state's boundary with North Dakota. Finally, in 1969, these gems were jointly declared the state gemstones.[36][78]

Notable specimens

A 0.25 carat rectangular-cut cornflower blue Yogo sapphire.

There are a number of Yogo sapphires kept at the Smithsonian Institution. The first were noted in its annual report for the year ending June 30, 1899, when the Smithsonian reported that Dr. L. T. Chamberlain gave them 2 cut Yogos and 21 other sapphires, as well as other gems, for its Dr. Isaac Lea gem and mineral collection.[79] In 2006, a representative of the Smithsonian Institution asked Paula Crevoshay, a jewelry designer from Albuquerque, New Mexico, to create a piece of finished jewelry from a set of Montana sapphires. Gemologist Robert Kane of Fine Gems International in Helena, Montana, which has the largest selection of Montana sapphires in the world, donated these gems to the Smithsonian's Gem and Mineral Collection. He provided 333 Montana sapphires weighing 27.97 carats along with 98.48 grams of 18K yellow gold for the project.[80][81] Crevoshay felt that a butterfly motif would be excellent to represent America's natural beauty, honor her mother's love of butterflies, and display the wide range of colors found in Montana sapphires. Crevoshay named the brooch "Conchita" in honor of her mother. It is also referred to as the "Sapphire Butterfly Brooch", "Conchita Sapphire Butterfly", and the "Montana Butterfly Brooch". Two of the sapphires used are cabochon cut and the rest are brilliant cut. The majority are from the Rock Creek deposit. The largest one, however, is a blue Yogo used for the butterfly's head. Other colors used are yellow, purple, pink, and orange. Crevoshay and Kane presented it to Smithsonian curator Jeffrey Post on May 7, 2007 in Washington, D. C.[82][83]

In the earliest years of Yogo sapphire mining, before Yogos achieved their own reputation, Oriental sapphires were sold in Montana with claims they were Yogos while in Europe Yogos were sold with claims of being Oriental sapphires.[84] However, they became notable in their own right. Paulding Farnham (1859–1927) used these stones to great advantage in several jewelry pieces he designed for the 1900 Exposition Universelle in Paris,[85] where Yogo sapphires received a silver medal for color and clarity.[86] Yogo sapphires also won a bronze medal at the 1904 Louisiana Purchase Exposition in St. Louis, Missouri.[87] The most elaborate piece of jewelry ever made with Yogos is the Tiffany Iris Brooch that was designed by Farnham and contains 120 Yogo sapphires,[88] which was first sold on March 17, 1900 for $6,906.84.[89] In 1923 First Lady Florence Harding was given an "all Montana" ring made from a Yogo sapphire and Montana gold. Then in 1952 Gadsden gave cut Yogos to President Harry Truman, his wife Bess, and their daughter Margaret.[26] While there is no doubt many Yogos have been sold in Europe, there is dispute about whether they are in any of the crown jewels of Europe or whether Lady Diana Spencer's engagement ring sapphire was a Yogo. This same ring was also Kate Middleton's engagement ring. That sapphire has been reported as being 9, 12, and 18 carats.[36][90][91]

See also

Notes

  1. ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W. and Nichols, Monte C. (ed.). "Corundum". Handbook of Mineralogy (PDF). Vol. 3. Chantilly, VA, US: Mineralogical Society of America. ISBN 0962209724. Retrieved December 5, 2011.{{cite book}}: CS1 maint: multiple names: editors list (link) Note: sapphire is a color variety of corundum.
  2. ^ a b c McRae, W. C. (2009). Montana. Berkeley: Avalon. p. 339. ISBN 9781598800142. Retrieved October 29, 2011. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  3. ^ "Yogo Sapphire Jewelery". Montana Russell Country. Retrieved December 3, 2011.
  4. ^ a b c d Voynick 1985, p. 10
  5. ^ "Yogo Creek, near Yogo Gulch". Geographic Names Information System. United States Geological Survey, United States Department of the Interior.
  6. ^ "Field Guide, Little Belt Mountains". Science Education Resource Center, Carleton University. Retrieved October 29, 2011. Note: Click map
  7. ^ Weed, Walter Harvey (1900). Geography of the Little Belt Mountains, Montana. Washington, D. C.: United States Geological Survey, Government Printing Office. pp. 454–459. ISBN 9780750658560. Retrieved October 29, 2011. {{cite book}}: Unknown parameter |coautors= ignored (help)
  8. ^ a b Voynick 1985, pp. xii, 116
  9. ^ "Descriptions – County Boundaries" (PDF). Montana Legislature. p. 22. Retrieved November 5, 2011.
  10. ^ "Montana Highway Map" (PDF). Montana Natural Resource Information System. Retrieved November 5, 2011.
  11. ^ Voynick 1985, p. 116
  12. ^ Voynick 1985, pp. ix–xi
  13. ^ a b c Ward, Jane R. "Yogo Sapphires". Yogo Paydirt. Retrieved December 5, 2011. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  14. ^ a b c d e "Corundum". Department of Geological Sciences, University of Texas at Austin. 1998. Retrieved October 28, 2011.
  15. ^ a b Voynick 1985, pp. 6–8
  16. ^ a b c d e f g h i j k l m n o Kane, Robert E. (January/February 2003). "The Sapphires of Montana – A Rainbow of Colors". Gem Market News. 22 (1): 1–8. {{cite journal}}: Check date values in: |date= (help) Revised January 2004.
  17. ^ a b c Voynick 1985, pp. 31–32
  18. ^ Voynick 1985, pp. 62–63
  19. ^ a b c O'Donoghue, Michael (2006). Gems: Their Sources, Descriptions and Identification. Oxford: Butterworth-Heinemann. pp. 123, 144–146. Retrieved October 29, 2011.
  20. ^ a b c Kunz, Dr. George F. (1897). Kuna, Edward S. (ed.). "Sapphires From Montana, With Special Reference to Those From Yogo Gulch in Fergus County". American Journal of Science. 4. 4. New Haven, CT: Yale University Department of Geology and Geophysics: 417–420. Retrieved October 29, 2011. {{cite journal}}: |chapter= ignored (help)
  21. ^ Pratt, Dr. J. H. (1897). Kuna, Edward S. (ed.). "Crystalography of Montana Sapphires". American Journal of Science. 4. 4. New Haven, CT: Yale University Department of Geology and Geophysics: 424–428. {{cite journal}}: |access-date= requires |url= (help); |chapter= ignored (help)
  22. ^ a b c "Sapphires". United States Geological Survey. Retrieved October 26, 2011.
  23. ^ a b Voynick 1985, p. 193
  24. ^ Voynick 1985, p. vii
  25. ^ a b c d e Gibson, Richard I. (Summer 2011). "Yogos: Montana's "Goldilocks" Gem". Distinctly Montana. Retrieved October 29, 2011.
  26. ^ a b Voynick 1985, p. 204
  27. ^ Elliott, Thomas B. (May 2, 2011). "Montana Sapphire Vs. Yogo Sapphire". Jewelers Ethics Association News. 3 (8). Jewelers Ethics Association. Retrieved October 29, 2011.
  28. ^ a b c d e f g Harlan, Stephen S. (1996). "Timing and Emplacement of the Sapphire-Bearing Yugo Dike, Little Belt Mountains, Montana" (PDF). Economic Geology. 91. Society of Economic Geologists via George Mason University Academic Research System: 1159–1162. Retrieved December 17, 2011.
  29. ^ "Montana Sapphires – Gemology". Gem Gallery. Retrieved October 29, 2011. Note: Includes map of major Montana sapphire mines
  30. ^ Pirsson, L. V. (1897). Kuna, Edward S. (ed.). "Corundum-bearing Rock From Yogo Gulch, Montana". American Journal of Science. 4. 4. New Haven, CT: Yale University Department of Geology and Geophysics: 421–423. Retrieved October 29, 2011. {{cite journal}}: |chapter= ignored (help)
  31. ^ a b Sterrett, D. B. (1908). Mineral Resources of the United States, Calendar Year 1907, Part II Non-Metallic Products. Washington, D. C.: United States Geological Survey, Government Printing Office. pp. 816–819. Retrieved October 29, 2011.
  32. ^ Meyer, Henry O. A. (1988). "Sapphire Bearing Ultramafic Lamprophyre from Yogo, Montana: A Ouachitite" (PDF). Canadian Mineralogist. 26: 81–88. Retrieved December 19, 2011.
  33. ^ a b c d Voynick 1985, pp. 151–158
  34. ^ Recreational Map of Western Montana. Canon City, CO: Western GeoGraphics. 1990. p. 339. ISBN 0528925512. {{cite book}}: |access-date= requires |url= (help)
  35. ^ Ward, Jane R. "Roberts Yogo Sapphire Gems". Roberts Yogo Sapphire Mines. Retrieved November 25, 2011. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  36. ^ a b c d "State Gemstones Sapphire and Agate". Montana Department of Tourism. Retrieved November 6, 2011.
  37. ^ Voynick 1985, pp. 19–21
  38. ^ Voynick 1985, pp. 16–19
  39. ^ a b c d "Abandoned Mines Historic Context". Montana Department of Environmental Quality. Retrieved November 6, 2011.
  40. ^ Voynick 1985, pp. viii, 2–3
  41. ^ Voynick 1985, pp. 3–4, 29–31
  42. ^ Voynick 1985, pp. 31, 29–31
  43. ^ a b c Moser, Cathy (Spring/Summer 2009). "Yogo City or Bust". Big Sky Journal. Bozeman, MT. Retrieved October 24, 2011. {{cite journal}}: Check date values in: |date= (help)
  44. ^ Voynick 1985, pp. 32–35
  45. ^ Voynick 1985, pp. 109–112
  46. ^ Voynick 1985, pp. 74–76
  47. ^ a b Voynick 1985, p. 21
  48. ^ "Ringold, Millie (1845–1906)". Black Past. Retrieved November 2, 2011.
  49. ^ Taliaferro, John (1996). Charles M. Russell: The Life and Legend of America's Cowboy Artist (2003 ed.). Norman, OK: University of Oklahoma Press. pp. 34, 40. ISBN 0-8061-3495-X. Retrieved October 31, 2011. {{cite book}}: Invalid |ref=harv (help)
  50. ^ Paladin, Vivian A. "Facts and Reflections About Charles M. Russell". Art Montana. Retrieved November 6, 2011.
  51. ^ Voynick 1985, pp. 22–30
  52. ^ Voynick 1985, pp. 27–30, 110–113
  53. ^ "Utica (A Quiet Day in Utica) By Charles M. Russell". Sid Richardson Museum. Retrieved November 2, 2011.
  54. ^ "Yogo Sapphires". Russell Country. Retrieved October 31, 2011.
  55. ^ Boggs, Johnny D. (September 25, 2009). "Following Charlie Russell's Paintbrush". True West Magazine. Retrieved November 2, 2011.
  56. ^ a b c Voynick 1985, pp. 36–42
  57. ^ Voynick 1985, pp. 71–73
  58. ^ Voynick 1985, pp. 80–81
  59. ^ Voynick 1985, pp. 102–109
  60. ^ Voynick 1985, pp. 117–122
  61. ^ Voynick 1985, pp. 57–64
  62. ^ Voynick 1985, pp. 75–77, 95–96
  63. ^ Voynick 1985, pp. 76–78
  64. ^ Voynick 1985, pp. 122–130
  65. ^ Voynick 1985, pp. 125–134
  66. ^ Voynick 1985, pp. 134–135
  67. ^ Voynick 1985, pp. 136–138
  68. ^ Voynick 1985, pp. 138–144
  69. ^ Voynick 1985, pp. 144–150
  70. ^ a b c Voynick 1985, pp. 151–154, 158–164
  71. ^ a b Voynick 1985, pp. 165–181
  72. ^ Voynick 1985, pp. 181–185
  73. ^ Voynick 1985, pp. 185–191
  74. ^ Voynick 1985, pp. 193–195
  75. ^ Voynick 1985, pp. 196–198
  76. ^ Voynick 1985, pp. 198–201
  77. ^ Voynick 1985, pp. 201–207
  78. ^ "State Gem, Montana Code Annotated section 1-1-501". Montana Legislature. Retrieved November 9, 2011.
  79. ^ Board of Regents (1901). Annual Report of the Board of Regents of the Smithsonian Institution for the Year Ending June 30, 1899. Washington, D.C.: Government Printing Office. p. 32. Retrieved November 13, 2011. {{cite book}}: Invalid |ref=harv (help)
  80. ^ "Conchita". Smithsonian Institution. Retrieved November 13, 2011.
  81. ^ "Sapphire Butterfly Brooch". Smithsonian Institution. Retrieved November 13, 2011.
  82. ^ Crevoshay, Paula (February 2007). "Conchita – Inspiration and Process". Crevoshay. Retrieved November 13, 2011.
  83. ^ "Crevoshay, Kane Present Sapphire Treasure to Smithsonian" (PDF). Libertine Jewelry. May 7, 2007. Retrieved November 13, 2011.
  84. ^ Voynick 1985, pp. 62–64
  85. ^ Zapata, Janet (1991). "The Rediscovery of Paulding Farnham, Tiffany's Designer Extraordinaire, Part I: Jewelry". Antiques. 139 (3). Brant Publications: 561. {{cite journal}}: |access-date= requires |url= (help)
  86. ^ Voynick 1985, pp. 57–58
  87. ^ Voynick 1985, p. 93
  88. ^ Voynick 1985, pp. 114–115, 204
  89. ^ Johnston, William R. (1999). William and Henry Walters: The Reticent Collectors. Baltimore, MD: Walters Art Gallery. p. 271. ISBN 0801860407. Retrieved November 10, 2011.
  90. ^ Voynick 1985, p. 163
  91. ^ Wilkes, David (November 17, 2010). "A Ring Fit For His Mother...and His Love: Prince William's Sapphire and Diamond Engagement Ring for Kate". Daily News. Retrieved November 6, 2011. {{cite news}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

References

  • Voynick, Stephen M. (1985). Yogo The Great American Sapphire (March 1995 printing, 1987 ed.). Missoula, MT: Mountain Press Publishing. ISBN 0-87842-217-X. {{cite book}}: Invalid |ref=harv (help)

External links

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