Colorado's Sweet Home Mine: The Raspberry-Red Crystal Worth More Than Silver

High on the flank of Mount Bross, above the old mining town of Alma, Colorado, sits a mine that got everything wrong and then everything right. The Sweet Home Mine opened in 1873 to chase silver, and as silver mines go it was, frankly, a disappointment. What it produced instead — almost by accident — were raspberry-red rhodochrosite crystals so vivid and so perfectly formed that in 1991 the mine was reopened for a purpose with almost no precedent at commercial scale: not to dig ore, but to recover specimens. The finest crystals from the Sweet Home have since changed hands for more than the mine's entire silver output, and its most famous stone, the Alma King, sits in a Denver museum like a crown jewel.

A silver mine that never quite paid

The story begins in the early 1870s, when prospectors staked the Sweet Home claim on the slopes of Mount Bross in Park County, in the thin air of Colorado's Mosquito Range; by 1873 it was a working silver mine. Alma, the town below, remains one of the highest incorporated towns in North America, and winters up there are brutal. The miners were after silver, and there was some — just never enough. The mine changed hands repeatedly and was worked on and off for the better part of a century, opening whenever silver prices flickered upward and closing again when they slumped. By one accounting, the Sweet Home yielded roughly $215,000 worth of silver at the prices of the day across its entire life as an ore mine. For nine decades of dangerous, freezing, hand-drilled labour, that is a heartbreakingly small number.

By the mid-1960s the silver era was over. The mine was abandoned as a working proposition, one more half-forgotten hole in a state full of them. Except this particular hole had a secret the miners had known about all along.

The red crystals nobody wanted

From the earliest days, Sweet Home miners kept hitting pockets of a strange, glassy, cherry-red mineral: rhodochrosite, a manganese carbonate that takes its colour from the manganese itself. To a silver miner it was a nuisance — pretty, but worthless as ore. Yet the crystals were striking enough that specimens were reaching major museum collections in the eastern United States by the late 1880s. A spectacular pocket found in 1926 cemented the mine's reputation among mineral collectors, and in late 1966 — right at the end of the silver era — a crew drilled into a pocket holding the "Alma Queen", a specimen so fine that one prominent collector of the day flatly called it the best mineral specimen in the world. It now lives at the Houston Museum of Natural Science.

Rhodochrosite itself is not rare. It is found in Argentina, where it forms banded pink layers known as Inca Rose, and in South Africa, Peru, Romania and elsewhere. What is rare — vanishingly rare — is what the Sweet Home produced: large, transparent, intensely red rhombohedral crystals, sharp as if machined, perched on beds of needle-quartz, purple-blue fluorite and brassy sulphides. In that specific form, this unglamorous carbonate becomes one of the most coveted display minerals on Earth. It is a good reminder that fame in the gem world attaches to specific stones as much as to species — the same reason a handful of individual diamonds became the most famous diamonds in history while millions of others stayed anonymous.

1991: a mine reopened for beauty, not ore

Then comes the turn nobody in 1873 could have imagined. In 1991, Bryan and Kathryn Lees of Collector's Edge Minerals, backed by a group of investors, leased the old workings and reopened the Sweet Home under a new company, Sweet Home Rhodo, Inc. The business plan was radical in its simplicity: mine the mountain purely for collector specimens. No smelter, no concentrate, no ore trucks — the product was the crystal itself, intact, on its natural matrix.

That changes everything about how you mine. Blasting, the ordinary language of hard-rock mining, becomes the enemy, because a single shockwave can shatter a pocket worth a fortune. The Sweet Home crews developed remarkably gentle methods — careful drilling, low-energy rounds, diamond saws, and painstaking hand extraction — sometimes spending weeks stabilising and emptying a single cavity. It was closer to palaeontology, or surgery, than to mining. And it worked. Over thirteen years the operation recovered thousands of world-class specimens; by the operators' own estimate, the cumulative value of rhodochrosite taken from the Sweet Home across its whole history runs past $100 million. Set that against $215,000 of lifetime silver, and the mine's real treasure is not in doubt.

The Alma King

The operation's defining moment came on 21 August 1992, when miners broke into a cavity that became known as the Rainbow Pocket, its walls glittering with quartz, fluorite, calcite and metallic sulphides. From it came a single rhodochrosite rhombohedron measuring roughly 14 by 16.5 centimetres — about the size of a grapefruit, cherry-red, and astonishingly sharp-edged. Christened the Alma King, it remains the largest known rhodochrosite crystal in the world. Over the following weeks the pocket gave up hundreds more fine specimens, among them the King's smaller sibling, the Alma Rose, now at the Rice Northwest Museum of Rocks and Minerals in Oregon.

The Alma King belongs to the Denver Museum of Nature & Science, where it has long been the signature piece of the gems and minerals hall. (If you're planning a pilgrimage, time it carefully: the hall closed in April 2026 for a $30 million renovation and is due to reopen in 2027 as the expanded Dea Family Gems & Minerals Hall.) The mine's own story took longer to end than most tellings admit. The original portal was sealed in 2004, but in 2016 Collector's Edge opened a new entrance a little higher up the mountain — the Detroit City Portal — and coaxed out further pockets until 2024, when that portal, too, was closed for good.

How schoolchildren made it the state mineral

Rhodochrosite's final honour came not from geologists but from teenagers. In 2002, an earth science class at Platte Canyon High School in Bailey, Colorado, taught by John Ghist, realised their state had no official mineral. The students debated candidates and settled on rhodochrosite — partly for the elegant coincidence that "Colorado" comes from the Spanish for "coloured red". They wrote to State Representative Carl Miller, who introduced a bill; it passed with Senator Ken Chlouber's sponsorship, and on 17 April 2002 Governor Bill Owens signed rhodochrosite into law as Colorado's official state mineral. From classroom letter to statute in about three months — a civics lesson most textbooks can't match. It sits nicely alongside America's other great everyman gem story, the dig-it-yourself diamond field at Crater of Diamonds State Park in Arkansas.

The honest bit: can you actually wear rhodochrosite?

Here is where we have to be straight with you. Gem-grade rhodochrosite can be faceted, and a top Sweet Home stone glows like red neon — but it is one of the most fragile gems a cutter ever touches. On the Mohs scale it sits at roughly 3.5 to 4, softer than a steel knife and not far above a copper coin. Everyday dust contains quartz at hardness 7, which means ordinary wear will scratch and dull a rhodochrosite over time. Worse, it has perfect cleavage in three directions — internal planes along which a knock can simply split it — and, being a carbonate, it is vulnerable to even weak acids: vinegar will etch it, and cosmetics and sprays can dull its lustre.

Faceted rhodochrosite is therefore a collector's gem: kept in a case, occasionally set in a pendant or earrings, handled with real care. As an engagement ring stone worn daily on a hand, it would be heartbreak on a timer. If you're weighing what different stones can survive, our diamond and stone guide walks through hardness, toughness and wearability in plain terms.

We love the Sweet Home story because it proves that value in gems is about rarity, beauty and story — not just what a smelter will pay. But it also shows why, for a ring meant to survive decades of daily life, hardness is not negotiable. That's why we work only in diamond, the hardest natural material there is, grown in modern labs and crafted to order in our Surat workshop, each stone IGI-certified with its report number laser-inscribed on the girdle. If a lifetime-proof red accent or a classic centre stone is on your mind, our engagement ring guide is a calm place to start. Rhodochrosite belongs in a museum case; your ring belongs on a hand.