By: Marlene Affeld
Brilliant, beautiful and highly prized, the Yogo sapphire is the most precious gemstone mined in the United States and is an official gemstone of Montana. Breathtaking to behold, the Yogo sapphire is found only in Montana.
Yogos are unique among the sapphires of the world. Whereas most of the sapphires found around the world vary greatly in color and quality, the Yogo sapphire’s unusual “corn-flower” blue color is natural (rather than heat treated) and color and clarity are uniformly high. Yogos are nearly flawless. Another unusual quality of Yogo sapphires is that they retain their magnificent brilliance under artificial light. The majority of Yogo sapphires are the signature blue; however, exceptionally beautiful shades of purple are occasionally found.
Rough stones are generally quite small, flat and wafer-like in shape. The majority of the crystals or pieces of crystal discovered to date are too small to be cut. Most stones are less than 1 carat and anything over 2 carats is extremely rare. The largest crystal ever found was a 19 carat stone that in 1910 was crafted into an 8 carat gemstone. The largest cut Yogo is 10.2 carats and resides in the Smithsonian Institution in Washington, D.C. Rarer than diamonds, Yogo sapphires are coveted, exquisite, expensive jewels.
Fifty million years ago the cataclysmic geological events that crafted our great state caused rocks, buried deep beneath the earth’s crust, to melt into masses of molten magmas. One of these magmas, located on the northeastern side of the Little Belt Mountains of Central Montana, rose into the Madison Limestone deposit where it slowly cooled to form a lamproite dike. This gigantic dike intruded a fissure in the earth to form the world’s largest deposit of gemstone quality sapphires, the Yogo Dike.
Located near the historic town of Utica, Montana, in Judith Basin County, the Yoga Dike varies from 8 feet to 100 feet wide and stretches over five miles in length. Although recent geological surveys indicate sapphire reserves in the Yogo Dike at depths in excess of 7000 feet, mining to date has not gone beyond approximately 250 feet. Geologists estimate that as much as 28 million carats lie beneath this huge overburden. It is impossible to fathom the size, clarity and value of the treasure still buried.
When the magma in the Yogo Dike crystallized, atoms of oxygen and aluminum merged to form corundum, the mineralized form of aluminum oxide. The word corundum is derived from the Sanskrit, kuruvinda (Ruby). The corundum formed exquisite, perfectly shaped transparent crystals. Traces of titanium and iron within the molten magmas provide the naturally occurring rich cornflower blue colorization.
The Yogo Dike is Montana’s only primary corundum source. In mining terminology “primary” means that the gemstone being mined remains embedded in the rock where it was formed and that rock has not migrated from its original location. When the host rock has eroded and the gems have been transported by rock slides or water to another area, the new site is called a secondary source or a placer deposit.
History of Sapphires in Montana
The discovery of sapphires in Montana was a result of the gold rush of the 1860’s. Thousands of prospectors, seeking the elusive mineral, converged upon the area to pan the gravel bars and stream beds. Those prospectors, with experience gained in the great California gold rush, quickly constructed wooden sluice boxes to separate the gold from the gravel. Sapphires, being heavier than the gravel, collected in the bottom of their concentrates and clogged the sluice boxes. These translucent pebbles were simply a nuisance and were quickly cast aside in their frantic search for gold.
Gem quality corundum that is not red in color is called sapphire. Sapphires are white, yellow, orange, green, blue, violet and sometimes pink. The small multi-colored stones that angered early placer miners by clogging gold sluices in such places as El Dorado Bar east of Helena were considered worthless.
An old-timer named "Sapphire Collins" wandered the streets of Helena in the 1860's with a pocket full of pretty pebbles. Try as he might to convince bankers, bartenders and local merchants of the stones' value, he was rudely told that gold was the only thing from the creek they would trade for, anything else was of no merit.
In 1865 Ed Collins, a savvy trapper and prospector, took a second look at the pebbles the miners were discarding and correctly identified the stones as sapphires. Believing he had “struck it rich”, Collins excitedly gathered up a packet of the stones and shipped them to both Fox and Tiffany Jewelers in New York City. His hopes were dashed when the jewelers responded that the stones were of inferior quality and worthless. The stones found by Ed Collins were from the gravels of the Missouri River in Lewis and Clark County, Montana and did not have the clarity and color of jewelry grade stones. Subsequent discoveries were recorded in 1889 on Dry Cottonwood Creek in Deer Lodge County and on Rock Creek in Granite County in 1982.
Farsighted financiers soon learned of Montana sapphires and substantial companies from as far away as England invested in sapphire mines throughout the state. On Rock and Quartz Creeks west of Philipsburg, at Brown’s Gulch and Dry Cottonwood Creek east of Anaconda and along the Missouri River at French Bar, El Dorado Bar, Metropolitan Bar and Magpie Gulch, the rush was on! However, the “glory hole” was soon to be found in the lush green drainage called Yogo Gulch.
Almost thirty years after the original “discovery” of sapphires in Montana, history repeated itself. In 1894, mountain man, trapper, friend of artist Charles Russell and sometimes prospector, Jake Hoover was working a gravel bar on Yogo Creek located 45 miles southwest of Lewiston, Montana. Ironically,Yogo is a beautiful word in the Piegan Blackfoot Indian language which means “blue sky”.
Although he had seen sapphires many times before, the blue stones, “sparkling clear and the color of a Montana Sky”, that appeared in the bottom of his gold pan were uniquely different. Jake continued to work his claim, finding some gold and patiently saving the “little blue rocks” until he had filled a cigar box.
Believing he had found a worthy deposit, Jake Hoover shipped his find to George Kunz of Tiffany and Company Jewelers in New York. He was elated when he received a check for $3750 for “sapphires of unusual quality”. Hoover quickly formed the New Mine Sapphire Syndicate.
A London jewelry conglomerate soon purchased all the shares in the mine and changed the name to the English Mine. Commercial mining for the valued sapphires at Yogo commenced in 1896. Charles T. Gadsden, an English mining engineer, oversaw the operation at Yogo. Shortages of water and workers all but halted production of the mine during World War I. Double taxation by both the British and United States governments curtailed profits and in 1923 a devastating storm caused considerable damage. The Yogo Mine was closed in 1929 and not worked again until 1956.
By the time the mine was closed in 1929, Yogo had produced 2.5 million carats of gem quality sapphires, valued at over 25 million dollars. The mines of Yogo Gulch are currently being worked by commercial companies. The accumulated value of these precious blue gems is now in excess of 40 million dollars. The demand for Yogo sapphires, particularly for the larger carat sizes, far exceeds production.
The Yogo sapphire, named one of our states gemstones in 1969, is a treasured part of history of which Montanans can be justifiably proud.