Ojuela Mine, Mexico — adamite with yellow-green pinwheel crystals, blue cuprian and purple manganoan varieties, strong UV fluorescence, a top collector locality
Key facts
Adamite from the Ojuela Mine is one of the signature mineral classics of Mexico: bright yellow-green crystal crusts and rosettes sparkling against iron-rich gossan, with forms that can be delicate enough for a thumbnail and rich enough to cover cabinet plates. At its best it has the particular Ojuela look serious collectors recognize instantly—lustrous, chisel-ended crystals or rounded sprays perched in cavities of reddish-brown limonite and goethite, often with a liveliness that survives even on older specimens.
Photo: Daderot, Wikimedia Commons
The reason Ojuela adamite became a benchmark lies in the mine’s geology as much as in its color. Ojuela is a great oxidized lead-silver-zinc replacement system in limestone, with arsenic-rich primary sulfides altered through deep and complex supergene zones. That oxidation made the mine a world locality not just for adamite but for a broader suite of arsenates—legrandite, lotharmeyerite, paradamite, ojuelaite, mapimite, metaköttigite, scorodite, carminite, austinite, and others. Adamite is the collector-friendly face of that chemistry: zinc, arsenate, and hydroxyl locked into crystals that can be lemon-yellow, yellow-green, colorless, bluish green when copper-bearing, or pink to violet where manganese is involved.
For connoisseurs, the locality is especially important because it produced several different “generations” and styles of adamite. The classic material is yellow to yellow-green and may form sparkling botryoidal-looking crusts made of radiating crystals, isolated fans, or rounded clusters. Cu-bearing examples can show blue-green tips or zones. The rarest and most romanticized pieces are the purple to lavender manganese-bearing adamites, especially from the famous early-1980s San Judas material, where crystals can show pale bodies with gemmy purple terminations or more saturated purple sprays. Those pieces are not merely color variants; they are part of the folklore of modern Mexican mineral collecting.
Photo: Rob Lavinsky/iRocks.com, Wikimedia Commons
Ojuela adamite is also loved by fluorescent-mineral collectors. Many specimens fluoresce bright green under shortwave ultraviolet light, and some respond under longwave as well, though intensity varies markedly from specimen to specimen. Fine daylight color, fluorescence, crystal sharpness, and matrix contrast can all occur in the same piece, which is one reason Ojuela remains a staple locality even for collectors who already own adamite from Tsumeb, Laurium, Gold Hill, or Cap Garonne.
Search for specimens: View all adamite specimens from Ojuela Mine, Mexico
The Ojuela Mine lies in the Mapimí district of Durango, at the northeastern escarpment of the Sierra de Mapimí, near the town of Mapimí in northern Mexico. It is not a small single adit locality in the collector’s sense, but a large mine system with named workings, stopes, shafts, chimneys, and sublocalities. Historical descriptions emphasize its scale: one early account says that a person could spend weeks underground without retracing the same passage.
Geologically, Ojuela is a limestone-replacement deposit typical of the great northern Mexican Ag-Pb-Zn systems. Primary mineralization replaced favorable carbonate horizons and filled fracture-controlled bodies, forming large pipes, caves, chimneys, and mantos separated by barren limestone. The primary sulfide assemblage included arsenopyrite, pyrite, sphalerite, and argentiferous galena, with calcite, quartz, fluorite, and limonite among the important gangue minerals. Later oxidation transformed this arsenic-bearing sulfide environment into the extraordinary secondary arsenate assemblage for which Ojuela is famous.
The mine’s working history reaches back to the Spanish colonial period. Modern mineralogical accounts describe shallow workings for rich secondary silver ores by about 1600, while Mexican heritage and tourism sources tie the founding or discovery of the Ojuela mine to 1598. In 1893 the property was converted into a major lead-silver operation by the American Metals Company. By the time Mary Mrose, Dan Mayers, and Francis Wise described Ojuela adamite in 1948, almost four million tons of ore had been mined from the property, with reported average assays of 3.7 grams gold, 462 grams silver, and 14.9 percent lead. Large-scale operations had already ceased by then because of drainage problems and depletion of reserves, while later work continued through smaller-scale and cooperative mining.
The named workings matter to collectors because Ojuela specimens are often tied to specific places inside the mine. The literature records workings such as Cumbres, Esperanza, Ojuela on the 15th level, San Judas on the 13th–14th levels, San Diego, San Pointe on the 14th level, Santo Domingo on the 5th level, and the Socavón shaft, with entrances including Americana, Americados, Norte, and Ojuela. Later specimen lore adds places such as Las Palomas and San Judas Chimney to the adamite story. The 1946 yellow-green adamite pocket was found in the Las Palomas ore body just above the 11th level, while the celebrated purple adamites are tied to the San Judas area and to work by Mike New and his miners.
Today, Ojuela is also a heritage and adventure-tourism site. The famous suspension bridge and mine tour draw visitors, but that public tourist experience should not be confused with collecting access. Serious specimen recovery has historically been episodic and permission-based, tied to miners, mine operators, dealers, and specific working campaigns. Collectors should assume that legal collecting underground or on mine dumps requires local authorization and current guidance.
Notable finds include the 1946 pocket of yellow-green adamite that produced a large U.S. National Museum specimen and Harvard examples; the rare purple manganese-bearing adamite from the early 1980s; blue-green Cu-bearing adamite; and abundant later market material in crusts, sprays, balls, and vug linings. Ojuela’s adamite story is inseparable from its larger arsenate suite: legrandite, scorodite, lotharmeyerite, austinite, conichalcite, paradamite, and several type-locality species give context to even a modest yellow-green adamite cluster.
Most classic Ojuela adamite is Zn2(AsO4)(OH), commonly forming radiating crusts, fan-shaped rosettes, sparkling druses, rounded clusters, and individual prismatic to wedge-shaped crystals. Early scientific work on the Las Palomas material described crystals commonly merged together as radiating crusts or fan-shaped rosettes on limonite, with individual crystals elongated parallel to [010]. In that 1946 pocket, measured crystals ranged from about 0.5 mm to 8 mm in the crystallographic study, while the pocket itself produced crystals reported up to about 5/16 inch long.
The usual color range is water-clear to pale yellow, lemon-yellow, yellow-green, and greenish yellow. The familiar collector look is yellow-green adamite sparkling on brown limonite or gossan. Some specimens show paler yellow crystals in vugs or crusts, and many older pieces are more about texture, coverage, and luster than large isolated crystals. Better cabinet specimens show continuous, undulating crystal crusts or pockets lined with dense, glassy, sharply terminated crystals.
Cu-bearing adamite from Ojuela introduces blue-green to green zones, often strongest toward terminations or as smaller associated crystals on the same limonitic matrix. These should not be judged by the same standards as ordinary yellow-green plates: good Cu-bearing examples are prized for color contrast, zoning, and fluorescence as much as for crystal size.
Manganese-bearing adamite is the elite color variety from the locality. The best pieces show lavender, pink-purple, violet, or maroon-purple color, sometimes as purple terminations over paler or yellowish crystal interiors. Collectors should note that Ojuela’s pink to violet adamite is manganese-bearing, not cobalt-colored. Older labels and casual descriptions may use “cobaltoan” language, but the accepted explanation for the pink-violet color at Ojuela is minor manganese.
Typical matrix is limonite, goethite, gossan, or altered limestone. The iron-rich matrix is not incidental: it gives the adamite its best visual contrast and records the oxidized environment that made the arsenate suite possible. Associated species documented with Ojuela adamite include calcite, hemimorphite, limonite/goethite, mimetite, scorodite, austinite, legrandite, gypsum, lotharmeyerite, smithsonite, chalcophanite, arseniosiderite, and other secondary arsenates or oxides. Combination pieces with strong, identifiable associates are especially attractive when the paragenesis is coherent rather than simply “mixed Ojuela matrix.”
Quality factors begin with luster and crystal freshness. The best adamite crystals look glassy rather than sugary or dull, with undamaged terminations and crisp chisel-like faces where the habit allows. Color should be vivid and natural-looking: yellow-green should not be merely brownish or muddy, Cu-bearing material should have convincing blue-green zones, and manganese-bearing material should show real lavender to purple saturation rather than weak staining or ambiguous pinkness. For ordinary Ojuela adamite, coverage and contrast matter: a lively carpet of small lustrous crystals can outrank a larger but duller piece. For purple material, even thumbnails can be important if the crystals are sharp, saturated, and well placed.
Size expectations differ by style. Common yellow-green druses and crusts occur from thumbnails through cabinet specimens, with many attractive miniatures and small cabinets on the market. Individual crystals in ordinary material are often millimetric, though some pieces carry larger crystals or clusters. Purple manganese-bearing adamites are commonly judged at a much smaller scale; crystals of several millimeters are collectible, while sharp crystals around 1 cm or more, especially in aesthetic sprays, are significant. Reported exceptional purple crystals to roughly 1.5–2 cm appear in older collection and dealer records, but such pieces are not everyday market material.
Fluorescence is a useful added character but not a guarantee of value. Many yellow-green Ojuela adamites fluoresce bright green under shortwave ultraviolet light, and some also respond under longwave. The response can vary widely even within the locality. Trace elements that create attractive daylight colors may also dampen fluorescence, so a weakly fluorescent purple or Cu-bearing specimen is not automatically suspect. For fluorescent-mineral collectors, however, a daylight-aesthetic Ojuela adamite that also glows strongly is a particularly satisfying specimen.
Ojuela adamite is common enough that every serious Mexican suite can include a representative example, but the locality spans a wide market range. Small yellow-green druses and modest clusters remain readily available. Fine cabinet plates with rich coverage, excellent luster, and undamaged surfaces are less casual purchases. Cu-bearing adamite is scarcer and more specialized. Purple manganese-bearing adamite is in a different category: desirable miniatures and thumbnails are tightly held, and well-colored, well-formed examples from the early-1980s material bring strong competition.
The first authenticity issue is locality inflation. “Ojuela” is one of the best-known Mexican mineral names, and material from other Mexican localities has historically been sold or relabeled as Ojuela. This problem is well documented for some Mexican species and localities, and it matters for mixed dealer lots. For adamite specifically, visual fit is often good—yellow-green adamite on limonite is very characteristic—but labels with old collection provenance, mine sublocality, or reputable dealer history add confidence. Generic “Mapimí” may refer to the district rather than a precise pocket or mine level.
The second issue is varietal naming. Pink to violet Ojuela adamite should be treated as manganese-bearing adamite, not cobalt-bearing adamite, unless supported by analysis. Older “cobaltoan adamite” labels on purple Ojuela material should be corrected or at least annotated. For collection catalogs, “adamite var. manganese-bearing adamite” or “manganoan adamite” is the safer designation.
No major, well-established treatment problem is specific to Ojuela adamite in the way that artificial coloring is documented for some other Ojuela-labeled minerals. However, the broader locality has known pitfalls: artificially colored electric-blue hemimorphite entered the market, and some supposed Ojuela kobyashevite has been questioned as man-made. Those examples are reminders that Ojuela labels alone do not validate every bright or unusual mineral from the mine. Adamite should be evaluated by crystal habit, color distribution, matrix, fluorescence behavior, and—when dealing with rare purple or blue-green pieces—provenance and, ideally, analytical confirmation.
Condition is often the deciding factor. Adamite is not extremely soft, but many Ojuela specimens are built from dense carpets of small protruding crystals on crumbly gossan. Edge wear, bruised terminations, rubbed high points, and iron oxide dusting are common. Examine vug lips and exposed ridges carefully. On plates, look for areas where crystals have been knocked off, leaving dull scars in an otherwise sparkling surface. On purple pieces, tiny termination damage can be difficult to see because the crystals are often small and strongly lustrous; magnification is worthwhile.
Cleaning should be conservative. The matrix may be porous iron oxide or limonitic gossan, and associated arsenates or carbonates can be sensitive. Avoid aggressive acids and prolonged soaking unless you have experience with the exact assemblage. Dust can be removed with air, a soft brush, and careful mechanical cleaning, but “improving” Ojuela adamite is usually more likely to reduce value than increase it.
As a handling note, adamite is an arsenate mineral. It is stable as a mineral specimen under normal collecting conditions, but avoid inhaling dust, do not cut or grind it without appropriate controls, keep it away from children who might mouth specimens, and wash hands after handling friable pieces.
In June 1946, Dan Mayers and Francis Wise were moving through the Las Palomas ore body just above the 11th level, on the way to a stope known for wulfenite and green mimetite, when their lamps caught something unexpected in a small manway. In the limestone was a pocket roughly four feet across and four feet deep. They described it as a “miniature grotto,” carved into fantastic shapes and coated over its entire surface with undulating waves of sparkling yellow crystals.
The scene reads like the kind of discovery collectors imagine but rarely see documented by the people who were actually there. The pocket was not a few loose specimens in rubble; it was a crystal-lined cavity large enough to work. Miners were set to the task immediately. The largest piece weighed 75 pounds underground and was nearly three feet square, with a continuous crust of green adamite crystals about a quarter-inch in size on brown limonite. After trimming, that specimen went to the U.S. National Museum. Two other important specimens went to Harvard.
The Las Palomas pocket also tells a mineralogical story. The adamite occurred in an elbow of the ore chimney, a place where descending zinc-rich solutions could stagnate rather than rush through. Hemimorphite was abundant nearby between the 11th and 12th levels, indicating the availability of zinc in the oxidized system, though it was not found directly with the adamite. Smithsonite was present only sparingly. That stillness—zinc-rich solutions, arsenate chemistry, a protected limestone pocket, and time—made the Las Palomas find one of the early reference points for Ojuela adamite.
Decades later, a different color made Ojuela folklore. Mike New, a Tucson mineral dealer and specimen miner, had permission to mine and export Ojuela specimens, and his work at the mine became part of the modern history of Mexican collecting. In 1981, in the San Judas chimney, his miners encountered fabulous purple adamites. The find became famous not because it produced tons of material, but because the color was so unexpected and so difficult to duplicate: lavender to purple manganese-bearing adamite, in crystals that could show pale bodies, gemmy purple terminations, zoned interiors, and sharp sprays on dark gossan.
Those specimens dispersed into museums and private collections around the world. Later records of purple adamite often read like provenance notes from a small, jealously guarded family: John Whitmire, Mike New, Willard Perkins, Dave Stoudt, George Elling, Ron Pellar, Peter Megaw, and other collector names recur on labels and dealer descriptions. A good purple Ojuela adamite is not just a pretty color variant; it is a piece of that 1980s specimen-mining episode.
There is also a postscript in the name mikenewite. The new mineral mikenewite was described from the San Judas Chimney and named for Michael Edwin New, whose best-known Ojuela achievement was that 1981 purple adamite find. The type material is associated with goethite, cryptomelane, adamite, and lotharmeyerite. In that way, a rare sulfite mineral described in 2023 loops back to the same working and the same man whose name collectors already associated with Ojuela’s most coveted adamite color.
