State Gemstones Sapphire and Agate

Updated: February 2, 2026

Montana sapphires and Montana agates have shared honors as the state's official gemstones since 1969, when the legislature passed a law naming both stones as state gem stones. Recognition was a long time in coming. A century earlier the small multi-colored sapphires angered early placer miners by clogging gold sluices in such places as El Dorado Bar east of Helena. "Sapphire Collins" frequented the streets of Helena in the 1860s with a pocket full of pretty stones. Try as he might to convince local merchants and bankers of the stones' value, he was told bluntly that gold was of prime importance and that anything else was of little worth.

Eastern and European financiers were not as shortsighted when they learned of Montana's sapphires in the early 1890s. Before long, substantial companies from as far away as London invested in sapphire mines throughout the state. On Quartz and Rock Creeks west of Philipsburg, on Brown's Gulch and Dry Cottonwood Creek east of Anaconda, and along the Missouri River at El Dorado Bar, French Bar, Magpie Gulch, Metropolitan Bar, and elsewhere, the rush was on. But the sapphire bonanza came at Yogo Gulch in central Montana's Judith Basin.

Jake Hoover, friend of cowboy artist Charles Russell, made one of the earliest discoveries of Yogo sapphires. Looking for gold, he found the blue pebbles in the gravels of Yogo Creek in 1895-1896. The Yogo mines attracted wide attention and capital, and the U.S. Geological Survey once termed the deposit "America's most important gem location." The British controlled much of the property for nearly thirty years, which helps explain why the beautiful "cornflower-blue" Yogos appear in royal and high-end European jewelry collections.

Yogo sapphires are prized because they are naturally colored, usually need no heat treatment, and show a rich blue that maintains its brilliance under artificial light, unlike some sapphires from other parts of the world that can look darker or dull indoors. From the late 1800s through the 1990s, the Yogo deposit produced an estimated many millions of carats of rough that may have yielded hundreds of thousands of carats of cut stones. Mining at Yogo has started and stopped many times; in recent years the claims have been redeveloped and promoted by modern companies that report renewed production of rough and cut Yogo sapphires for the jewelry market.

The largest known faceted Yogo sapphire is a 10.2-carat stone in the collection of the Smithsonian Institution in Washington, D.C., cut from an unusually large piece of rough discovered in the early 1900s.

Montana's Council of Rock and Mineral Clubs supported not only the sapphire for gemstone honors, but also advocated equal recognition for the exquisite and ever-varying Montana agate, found in abundance along the Yellowstone River and its tributaries in eastern and southeastern Montana. Montana agate (often called Montana moss agate) is a distinctive form of cryptocrystalline quartz, usually translucent white to pale gray with intricate black, brown, or red "mossy" patterns and banding created by iron and manganese oxides.

These agates formed in volcanic rocks tens of millions of years ago and were later eroded and carried down the Yellowstone River, where today rockhounds find them on gravel bars between Billings and Sidney and turn them into polished cabochons, beads, and jewelry. Cut and polished, both Montana sapphires and Montana agates are beautiful additions to jewelry and are much-sought-after gems.

Between the sapphire and the agate, Montana's east and west, mining heritage and rock-hounding hobby, and its long geologic story are all represented.

Special Acknowledgements to: Montana Historical Society, Rex C. Meyers and Norma B. Ashby

Updated: February 2, 2026