Updated: Oct 2, 2020
By Alissa Young, GG
On behalf of Milstead Gems LLC
As the Missouri River winds between rolling mountains dotted with verdant green pine and fir trees, its tumbling waters carry hidden gems. Sometimes referred to as “The Treasure State,” prospectors flocked to Montana in the 1860s in search of valuable gold. Large pebbles clogged the workers’ sluices, making the tedious process of gold mining even more difficult. The unknown stones, initially considered useless waste by the prospectors, were in fact precious sapphires (1). Over the next century and a half, Montana sapphires would rise from their humble beginnings to world renown and appreciation.
Perhaps the most famous Montana sapphire facet rough comes from Yogo Gulch. The only primary sapphire deposit in the region, these “Yogo” sapphires are prized for their vibrant and uniform blue to violet color and exceptional clarity without any heat treatment. When prospector Jake Hoover first discovered the remarkable stones at the end of the nineteenth century, he sent his finds to renowned Tiffany & Co. gemologist George Kunz for identification. Tiffany & Co. purchased the entire cigar box worth of stones for $3,750, cementing the famous jewelry company’s future relationship with the rare gem (2). The unique characteristics of Yogo Gulch sapphires make them prized by collectors, but they seldom produce faceted stones larger than a carat. The true range and diversity of Montana sapphire facet rough can only be found by exploring the state’s abundant alluvial deposits.
A 14-mile stretch of gravel bar along the Missouri River is home to several active deposits, with fully mechanized processing plants sifting through tons of gem-bearing gravel every day in search of precious sapphires (3). While Yogo Gulch gems are typically a classic cornflower blue straight out of the mine, sapphires found along the Missouri River gravel bars offer a broader assortment of hues, from subtle pastels to silvery neutrals. Careful heating can deepen or add color to these sapphires, creating deep blues and vibrant yellows. But modern trends have since embraced the softer rainbow hues of the natural, untreated alluvial gems. Best known for beautiful blue-to-green sapphires, these deposits also produce varied shades of yellow, green, purple, pink, and even the occasional ruby. Some rare sapphires found along the Missouri River contain traces of vanadium, producing a striking color change of blue to violet or purple. Others have been found with silky inclusions that create a six-rayed star effect known as asterism (1).
Rock Creek is yet another important secondary deposit in the region. Although the gems discovered there were originally deemed unmarketable as gemstones in their own right, they were considered perfect for watch movements and other mechanical parts. From 1906 until 1923, an estimated 190 million carats of sapphire were recovered from Rock Creek, much of it shipped to Switzerland for use in the watch industry (4). Production was reinvigorated in the 1990s, and an estimated 8-12% of sapphires recovered from the deposit are natural fancy colors, ranging in size from 2 mm to 1 inch. Frosted and etched surfaces suggest the crystals were brought to the surface by volcanic activity, with Montana sapphire facet rough concentrated in riverbeds and mudflows (5). In 2018, what may be the largest rough sapphire ever found in the US was unearthed here. Named the “Ponderosa Sapphire,” the 64.14 ct. blue-green gemstone bears a distinctive yellow core that is common to some Rock Creek discoveries that undergo heat treatment (6).
While their captivating hues are more than enough to make them beloved by jewelry professionals and gem lovers alike, Montana sapphire facet rough is also among the most ethically sourced rough in the industry. Not only are the full histories of the mines readily available, but they are also subject to the strict safety and humanitarian standards of the United States. Concerned about their impact on the environment, the mining companies themselves are dedicated to preserving the land. For example, at Rock Creek, old mine beds are replanted with local flora and restored to their original state, and the plant waste is recycled into road paving (5). Similar recovery projects are performed along the gravel bars, with each company taking care to not exploit the resources.
Once overlooked for their unconventional colors, Montana sapphires are now beloved for their myriad hues and singular look. Much like Kashmir, Ceylon, and Burma have become synonymous with fine-quality sapphires, Montana is rapidly gaining recognition for its own extraordinary facet rough.
Want Montana sapphire facet rough of your own? Check out Milstead Gemstone's sapphire collection, including pieces from the Treasure State but remember supplies are limited!
(1) “Why We Love Montana Sapphires and Yogo Sapphires.” International Gem Society. Accessed August 23,2020. https://www.gemsociety.org/article/montana-sapphires-yogo-sapphires/.
(2) “Gemological Characterization of Sapphires from Yogo Gulch, Montana.” GIA. Accessed August 23,2020. https://www.gia.edu/gems-gemology/summer-2018-gemological-characterization-of-sapphires-from-yogo-gulch-montana.
(3) “Big Sky Country Sapphire: Visiting Montana’s Alluvial Deposits.” GIA. Accessed August 23,2020. https://www.gia.edu/gems-gemology/summer-2017-montana-alluvial-deposits.
(4) “The Origin of Montana’s Alluvial Sapphires.” GIA. Accessed August 23,2020. https://www.gia.edu/gems-gemology/winter-2015-alluvial-sapphires-montana-inclusions-geochemistry-indications-metasomatic-origin.
(5) “Rock Creek Montana Sapphires: A New Age of Mining Begins.” GIA. Accessed August 23,2020. https://www.gia.edu/gia-news-research/rock-creek-montana-sapphires-new-age-mining-begins#item-4.
(6) “Potentiate Mining Unveils 64-Carat Montana Sapphire.” National Jeweler. Accessed August 23,2020. https://www.nationaljeweler.com/diamonds-gems/supply/7402-potentate-mining-unveils-64-carat-montana-sapphire.