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Yogo Sapphire

Hailing from Utica, Montana. These Montana sapphires have a unique cornflower blue color that is quite rare amongst our other Montana sapphires.


Yogo sapphires are a special variety of corundum found only in Judith Basin county, in a small area called Yogo Gulch.  Mining the elusive Yogo sapphires in this area has been much more difficult to mine than other Montana sapphire deposits due to the vertical dike they’ve been caught up in.  Many miners have tried to profit from these beautiful, sweet blue gems through the years but due to the tough terrain, most failed to be successful.

The Vortex Yogo mine was recently reopened after the previous owner, Mike Roberts, had passed away in a mining accident at this very location.  Luckily, the new owner has resumed operation and is making the lovely Yogo sapphires available to the public again.  Some speculate that although many Montana sapphires have been pulled from the Yogo Gulch, perhaps another 28 million carats of these sapphires still remain to be found. Today, several Montana sapphires are part of the Smithsonian Institutions gemstone collection including a Yogo over 10cts in size.


Montana Sapphires were first discovered in 1865, in the gravel along the Missouri River. Finds in other locations in the western half of the state occurred up to 1892, and 1894.  Yogo sapphires were not recognized or valued at first. Gold was discovered at Yogo Creek in 1866, and though “blue pebbles” were noticed alongside gold in the stream gravel by 1878.  It was not until 1894 that the “blue pebbles” were recognized as Montana sapphires.

Yogo sapphire mining began in 1895 after a local rancher named Jake Hoover sent a cigar box of blue gems he had collected to an assay office. The assay office then sent them to Tiffany’s in New York, where an appraiser pronounced them “the finest precious gemstones ever found in the United States”.  Tiffany’s fell in love with the Montana gemstone and is still a large retailer of the beautiful Montana Yogo sapphires today.  Hoover then purchased the location of the original mother lode from a sheepherder, later selling the sapphire mine off to other investors. This became the highly profitable “English Mine”, which flourished from 1899 until early 1920.

American Mine

A second operation, the “American Mine”, was owned by a series of investors in the western section of the Yogo dike. This yogo sapphire mine was less profitable and was bought out by the syndicate that owned the English Mine. In 1984, the Vortex mine opened and found montana yogo sapphires to be gemmy and plentiful.  Unlike the gem mountain sapphire mine, these gems didn’t need heat treating for color and clarity reasons.  Yogo sapphire mining in the Lewistown, Montana area was on a few miners bucket lists.

In the early 1980’s Intergem Ltd controlled most of the Yogo sapphire mining at the time. They started advertising the Yogo sapphire as the world’s only guaranteed “untreated” Montana sapphire. Thus revealing a common practice at that time wherein 95 percent of all the world’s sapphires were heat-treated to enhance their natural color. Although Intergem went out of business, the Yogo sapphire it mined appeared on the market throughout the 1990’s. Citibank had obtained a large stock of Yogo sapphire as a result of Intergem’s collapse.  They hoarded their stash of sapphire for nearly 10 years  before selling the collection to a Montana sapphire jewelry store in 1994. Sapphire mining activity today is largely confined to hobby miners in the area; the Vortex Yogo sapphire mine is the only major commercial mine currently in operation.


Yogo sapphires are mined in Montana at Yogo Gulch, 12 miles southwest of Utica, 45 miles west-southwest of  Lewistown and east of Great Falls.  The yogo sapphire mine site resides inside Judith Basin County and was carved out from parts of western Ferguson and eastern Cascade counties.  This minor change in county lines appears to have had no effect on yogo sapphire mining in the Lewistown area.

Yogo Gulch and the foothills of and including Yogo Peak, Yogo Creek, and the Yogo dike, are all in the Little Belt Mountains. The Gulch is located along the lower reaches of Yogo Creek and west of the Judith river. The west end of the Yogo dike shows up just southwest of Yogo Creek.  After about 3 miles north and half mile east until you stop short of the Judith river. Yogo Creek starts just south of Yogo Peak, which is about 15 miles west of the Judith River. From there the creek flows southeast into the Middle Fork of the Judith River.  The Judith River then flows northeast from the Little Belts toward Utica. Just east of the Judith River is Jake Hoover’s ranch; the person who discovered Yogo sapphires.


The term “Yogo sapphire” refers only to the Montana sapphires found in the Yogo Gulch sapphire deposit.  All other sapphires mined in Montana are just referred to as Montana Sapphires.  Yogo Sapphires are the only Montana sapphires still being mined from the primary deposit.  The Yogo sapphire’s typical cornflower blue color is a result of small amounts of titanium and iron. Yogos typically have good clarity and maintain their brilliance under artificial light.


The rare Yogo sapphire tends to be beautiful, small and quite expensive.  Montana sapphires come in at a 9 on the Mohs hardness scale, so they’re a gemstone that will withstand regular wear and tear but still be ready to hand down to future generations. The rough yogo sapphire crystal is often small and flat.  This makes finding any finished Yogo sapphire heavier than 2 carats quite rare.  The largest recorded Yogo sapphire rough, found in 1910, weighed 19 carats and was cut to an 8-carat gemstone.  The largest cut Yogo sapphire is 10.2-carat.  Luckily, regular Montana sapphire prices are more reasonable and come in a rainbow of colors!


The Yogo dike was a unique sapphire mining area compared to other sapphire sources in the world.  Unlike foreign sapphire deposits, all production records have been recorded.  Intergem had mined only around 700,000 carats of Yogo sapphire in the first 5 years.  Compared to the estimated reserves, what’s been mined is hardly a drop in the bucket.  The sapphire reserves have been based on only a depth of 500 feet and were estimated to be around 40 million carats of sapphire.  The actual depth of the dike however was estimated at over 7000 feet deep.  Without any exaggeration, the quantity of gem-quality blue Montana Yogo’s remaining in the dike could exceed the sum total of those remaining in all of the worlds other known sapphire deposits


Several years ago, we were lucky enough to get an invite to tour the Yogo sapphire mine.  At the time, our 3 boys were 10, 12 and 14 and this was going to be a real adventure for them-and an unforgettable experience for us all.  It was a long drive to the Judith Basin area.  Thankfully, we stopped for breakfast at a small cafe prior to driving the rest of the way to the mine. We drove out into the beautiful mountains to find the entrance to the Vortex Mine.  When we arrived, Mike greeted us and our fun was about to start.

We were all given hard hats and a brief explanation of what to expect. Then we put on our hard hats, climbed into the truck and headed into the darkness of the famous  Yogo sapphire mine.  Mike took us down winding tunnels into the dark to show us the seam where he was extracting the Yogo sapphire ore.  The sapphire material doesn’t occur in a very wide area but it was hopefully the location of the next big Yogo sapphire.  Along the way, we enjoyed beautiful calcite caves lined with sparkling crystals and found delicate mineral specimens that had formed deep inside the earth.  Mike’s genuine love for the Yogo sapphire was unmistakable and his enthusiasm was contagious.

Back up from the tunnels

Now that we had a better idea of where the Yogos were coming from, the next stop was the Jig.  Mike allowed our 12 year old to drive the mine cart out of the tunnels.  We left our boys in Mike’s hands (figuring our youngster couldn’t get too off track due to the narrow tunnel walls) and we headed up the tunnels back into the light. We got to see the trommel where all the dike material rolled around, hopefully releasing the yogos.  Then we headed up to see where the final, and most exciting work took place.  Lou, Mike’s good friend and helper as well as Mike’s kids showed us around the sapphire jig and we all got to help pick the lovely fine blue yogo sapphires out of the steel shot.

The Natural beauty of these gems never ceases to amaze me.  Our day was coming to a close so for the finale,  Mike let our boys hurl blasting sticks into the settling pond.  Although not actually necessary for sapphire mining, it was definitely a highlight for the boys. We’d seen an actual, underground mine.  We got to see the trommel where all the dike material rolled around, hopefully releasing the Yogo sapphires.  And we saw the seam of  host material where the Yogo sapphires came from from.  Our tour showed us how the Yogo sapphires were released from their hardened host material and how the miners then recovered those sapphires out of the jig. It’s a long process and Yogo’s are the most difficult sapphires to mine in all of Montana so we felt fortunate to have seen the process.

After a long day touring the Yogo sapphire mine, we were all pretty tired and extremely hungry.  Mining activities can take a lot out of you!  We sadly left the Vortex mine, figuring we wouldn’t get another experience like this anytime soon.  We were absolutely correct.  Not 6 months later, Mike had a fatal accident in the mine, changing Yogo sapphire mining as we knew it.

 “The Finest Sapphire in the world…Bar None” ~ Per the late Mike Roberts.