Montana is called the “Treasure State” for good reason. An 1863 gold strike heralded a long history of mining in Montana that continues today with palladium and platinum discoveries.  Add silver, copper, coal, bentonite, sapphires, and garnets to the list and you have a picture of the magnitude of mining that has happened in Montana over the years. 

On a recent southwestern Montana road trip with my older sisters, we were lured into prospecting for sapphires and garnets. Mining is in our DNA. Our great-great-great-grandfather joined the gold rush in Virginia City in 1863, years before Montana became a state.

Here’s what we learned on our hunt for gemstones:

1. The Geology

Sapphires were formed miles below the earth’s surface somewhere between 150 and 200 million years ago. As the tectonic plates moved, sapphires came to the earth’s surface and, in Montana, were washed off mountains into river and stream beds. 

Sapphires are among the “Big 3” gemstones. The other two are emeralds and rubies. They are considered precious gemstones because of their rarity. Those of you with September birthdays are lucky to have them as your birthstone. Sapphires are second only to diamonds when it comes to hardness and have been highly sought-after gemstones because of their beauty and durability.

Garnets, on the other hand, aren’t rare and aren’t nearly as hard as sapphires. They’re considered semi-precious gemstones and are January’s birthstone. While some garnets join silver, gold, and platinum in jewelry settings, many have industrial uses as abrasives in skid-free paint, on sandpaper, and in water jet sanders.

2. Where They’re Found

Sapphires are mined throughout the world. And in the U.S., they’re mined mainly in Montana. Hobbyists can mine for sapphires near Helena and Philipsburg. Yogo sapphires — prized for their clarity, deep blue color, and high value — are mined commercially near Lewistown.  

Our road trip took us to Philipsburg, so our first stop was Gem Mountain Sapphire Mine, 22 miles from Philipsburg, Montana. The mine is open during the summer months and requires reservations 24 hours in advance.

If you prefer to stay in Philipsburg, Montana Gems of Philipsburg, Sapphire Gallery, and Gem Mountain Sapphire bring gravel to their stores. You can pan for sapphires year round at these locations.

Garnets are found worldwide and in 21 states in the U.S., including Montana. Like sapphires, garnets rose to the earth’s surface. In Montana, this occurred in the Greenhorn Mountains. The garnets were delivered downstream by the Ruby River and its tributaries.

We mined for garnets at Red Rock Mine on Highway 287 six miles west of Virginia City. River of Gold on the outskirts of Virginia City also offers gold panning and garnet mining. It has old gold mining equipment onsite that you can check out, too.

3. Sapphires Come In A Rainbow Of Colors

When sluicing for gold — rinsing the dirt and sand from the “paydirt” — miners noticed colorful pebbles that settled at the bottom of the pan. Sapphires, like placer gold of similar weight, were heavier than the other stones. The miners paid little attention to them because they didn’t realize they were sapphires. They weren’t deep blue. Likewise, those we found weren’t deep blue. They ranged in color from pale yellow to light blue.

When sapphires formed, the addition of different minerals caused them to form in a rainbow of colors. Yogo Sapphires are a brilliant blue because of titanium. Chromium makes sapphires pink, and chromium plus iron makes them orange, and iron alone makes them yellow.

4. How To Find The Mother Lode

At both Gem Mountain Mine and Red Rock Mine, we chose our lucky bucket of gravel. We watched a demonstration on sluicing done in a waist-high trough. The process not only washes out dirt and sand, it encourages the sapphires and garnets to accumulate at the bottom of the sieve since they are heavier than the other pebbles. It takes a little practice rocking the sieve back and forth and gently bouncing it while it’s partially submerged in the water. My sister had a knack for it.

Luckily, she washed, rocked, and bounced the sieve properly so most of the sapphires and garnets landed in the bottom center of the screen. Turning the sieve over onto our table revealed a group of stones that looked like very pale colored sea glass in the case of sapphires — and red to maroon stones in the case of garnets. They were surrounded by the rest of the pebbles. We carefully picked through the gravel, but the vast majority of gemstones were easy to spot because of their location.

Pro Tip: If you aren’t able or comfortable with the sluicing process, Gem Mountain workers will help you every step of the way. It also provides wheelchair-accessible tables. 

5. Some Are Just Awesome Rocks

We took the sapphires we found to the Sapphire Gallery in Philipsburg for evaluation. Store representative Ashley Todd sorted our collection of stones. Some were just awesome rocks of the quartz variety and not gemstones at all. 

Steven Cox, owner of Red Rock Mine, evaluated our garnets onsite. He, too, separated out the garnets that could be faceted from those that weren’t garnets at all or were too small to use.

6. What Makes Them Worth Faceting

As both Ashley Todd and Steven Cox explained, the gemstone needed to be big enough to facet and clear enough to have value. This involved getting carat weights and looking at the stones with magnifying glasses to see how many impurities they had. Some of the sapphires and garnets we’d collected were too small, fractured, or imperfect to be worthy of faceting.

It came down to economics. If the cost to facet the stone was more than its value, it wasn’t worth cutting it. So, did we have any sapphires that could compete with Princess Di’s wedding ring? Not quite. But we did have nine sapphires (10.4 carats total) and four garnets (about 5 carats total) worth faceting. 

7. Heat Treating Sapphires Brings Out Their Best Color

In the 1980s, gemologists in Thailand discovered heat treating pale sapphires enhanced their color and clarity. Since that discovery, several million carats of naturally pale pastel Montana sapphires have been mined and heat treated.

We opted to have all nine sapphires heat treated and faceted. When we get together, we’ll divvy up the sapphires and the faceted garnets — probably letting age go before beauty — haha!

There are no guarantees in life or in mining, but I’m certain you’ll be enriched by the experience and memories you collect during your prospecting day.