Mimetite from the Ojuela Mine is one of the great color accents of the Mapimí suite: dense cushions of yellow, olive, apple-green, and dark green Pb5(AsO4)3Cl on rusty limonite, often brightened by small amber to butterscotch wulfenite crystals. The appeal is immediate and unmistakably Mexican—lead-arsenate color sitting on iron-rich gossan, with the velvety rounded texture of mimetite playing against the glassy, geometric faces of wulfenite.
Photo: Wikimedia Commons
Ojuela’s mimetite is not simply another yellow lead arsenate. The best pieces carry a green hue that is highly prized because it is uncommon for mimetite worldwide and visually distinctive for this mine. On strong specimens the mimetite forms rounded botryoidal “balls,” mammillary crusts, semi-spherical aggregates, or tightly sparkling druses that look soft and granular at a distance but resolve under magnification into lustrous microcrystalline surfaces. When wulfenite is present, the color contrast—orange-yellow molybdate crystals on green arsenate—is among the most recognizable Ojuela combinations.
The locality’s broader importance is much larger than mimetite alone. Ojuela is one of Mexico’s classic polymetallic oxidized replacement deposits, famous for arsenates and oxidation-zone minerals: adamite, legrandite, paradamite, köttigite/parasymplesite, hemimorphite, scorodite, rosasite, aurichalcite, wulfenite, calcite, fluorite, and many others. Mimetite fits naturally into that environment as a secondary lead arsenate formed in the oxidized portions of lead-rich ore bodies where galena, arsenopyrite, pyrite, and sphalerite supplied the ingredients for a remarkable secondary mineral suite.
For collectors, the sweet spot is an undamaged miniature to small-cabinet specimen with rich green or yellow-green mimetite, strong coverage, crisp relief, and well-placed wulfenite. Older orange-yellow hemispherical mimetite is also desirable, especially when lustrous and on contrasting limonite. The finest pieces have visual rhythm: rounded mimetite mounds, open pockets, iron-stained matrix, and a few sharp wulfenites set exactly where the eye wants them.
Photo: Wikimedia Commons
Search for specimens: View all mimetite specimens from Ojuela Mine, Mexico
The Ojuela Mine lies near Mapimí, Durango, at the northeastern escarpment of the Sierra de Mapimí. Mindat places the mine group at approximately 25°47'36" N, 103°47'27" W, in a hot desert climate. Collectors often use “Mapimí” and “Ojuela” almost interchangeably on older labels, but the precise and preferred locality is Ojuela Mine, Mapimí, Mapimí Municipality, Durango, Mexico.
Geologically, Ojuela is a limestone-replacement deposit typical of the northern Mexican polymetallic belt. Mineralization was controlled by fractures and favored certain dolomitic horizons. The principal ore bodies occurred as caves, pipes, and irregular replacement bodies separated by barren limestone. Primary mineralization included arsenopyrite, pyrite, sphalerite, and argentiferous galena, with calcite, quartz, fluorite, and limonite as important gangue minerals. That primary assemblage mattered enormously for mimetite: lead from galena, arsenic from arsenopyrite and arsenates, and chlorine-bearing oxidizing solutions produced the secondary lead arsenate Pb5(AsO4)3Cl in the mine’s oxidized zones.
The mining history is long and layered. The broader Ojuela camp is traditionally tied to Spanish discovery in 1598, and the mine was worked at shallow depths for rich secondary silver ores from about 1600 onward. In 1893 it was developed into a major lead-silver property by the American Metals Company. Contemporary mineralogical accounts record nearly four million tons of ore mined after that conversion, averaging 3.7 grams gold, 462 grams silver, and 14.9 percent lead. Later summaries of the full mining history credit Ojuela with more than six million tons of oxidized ore carrying roughly 90 million ounces of silver, 0.6 million ounces of gold, and 1.8 billion pounds of lead.
Large-scale ore extraction declined in the early twentieth century as reserves were depleted and drainage problems worsened. The old workings, however, continued to matter to collectors. The mine did not become internationally central to mineral collecting until W. F. Foshag’s 1927 visit, and significant specimen production accelerated after spectacular postwar discoveries in the 1940s. Since then, Ojuela has remained a sporadic but persistent source of fine specimens, usually through small-scale work rather than modern large-scale mining.
Ojuela is a mine complex rather than a single simple opening. Recorded workings and sublocalities include America Dos, America Poniente, San Juan Poniente, San Juditas, Santo Domingo, Level 7 of the La Campana Vein, San Judas Chimney, the Las Palomas ore body, and other named shafts, stopes, and levels. Mimetite has been specifically recorded from multiple sublocalities within the Ojuela system, including America Dos, America Poniente, Level 7 of the La Campana Vein, San Juan Poniente, San Juditas, and Santo Domingo.
Access should be treated seriously. Ojuela is a historic mining and tourist site with old underground workings, unstable areas, and local management. It is not a casual collecting locality. Specimens reaching the market generally come from old mine work, miner/collector activity, existing collections, or dealer stock, not from open public collecting. Collectors should not enter or collect in the workings without explicit local permission and competent underground guidance.
Ojuela mimetite is most famous in cabinet minerals for green color and rounded texture. Fine examples show olive-green, apple-green, yellow-green, or darker velvety green botryoidal crusts on limonite. The individual rounded aggregates commonly measure a few millimeters across, with documented specimen descriptions noting mimetite balls around 3–8 mm and larger semi-spherical groups reaching about 1.1 cm. On other pieces, the mimetite forms tighter drusy crusts, semi-botryoidal coverings, or small prismatic crystals around 1 mm in green clusters.
Yellow and orange-yellow mimetite also occur from Ojuela and can be just as attractive when lustrous. Older-style specimens may show vitreous orange-yellow hemispherical aggregates with small wulfenite crystals, while many of the better-known modern combinations feature darker green mimetite hosting orange, amber, caramel, butterscotch, or yellow wulfenite.
The most desirable association is wulfenite on mimetite. Thin tabular wulfenites, elongated blocky prisms, pseudo-cubic crystals, and prismatic to pyramidal crystals have all been recorded from Ojuela material. In strong examples, wulfenite crystals range from a few millimeters to over a centimeter, sitting on or partly embedded in green mimetite. These pieces work because the species contrast at every scale: soft rounded mimetite against sharp wulfenite geometry, matte to silky green against resinous orange-yellow, and bright secondary minerals against iron-brown gossan.
Common matrix is limonite or limonitic gossan, often vuggy and rusty brown. Calcite can provide a white crystalline substrate, especially in uncommon three-species combinations of calcite, mimetite, and wulfenite. Other associated species recorded with Ojuela mimetite or in close Ojuela parageneses include hemimorphite, cerussite, hedyphane, arsendescloizite, adamite, paradamite, goethite, and other oxidized lead-zinc-arsenate minerals.
Size range is broad but skewed toward thumbnails, miniatures, and small-cabinet specimens. Good thumbnails can be highly appealing if the green color is strong and the wulfenite is well placed. Miniatures around 4–5 cm are common in the market and can be very aesthetic. Small cabinets around 6–9 cm are desirable when coverage and condition are good. Cabinet plates exceeding 10 cm with rich green mimetite and wulfenite are much less common, especially if the display face is clean and the wulfenites are intact.
Quality depends on five factors: color, coverage, texture, association, and condition. The highest premium usually goes to saturated green mimetite, complete coverage over a sculptural matrix, crisp rounded or velvety aggregates, attractive wulfenite placement, and minimal bruising. Yellow and orange-yellow pieces are judged more by luster, form, and neatness of hemispherical aggregates. Because the mimetite often forms rounded crusts on iron-rich matrix, edge wear, scuffing, and pocket-contact areas must be evaluated carefully.
The main authenticity issue for Ojuela mimetite is not a standard treatment; it is locality attribution. Mindat’s Ojuela page records a specific warning that many minerals sold as Ojuela material actually come from other Mexican localities, including mimetite from Velardeña or Santa Eulalia. That warning matters because “Mapimí” and “Ojuela” are marketable names, and older labels can be vague. A specimen that is simply labeled “Mexico” or “Mapimi” deserves more scrutiny than one with an old collection label, sublocality, dealer history, or documentation tying it to Ojuela.
The green mimetite–wulfenite association is one of the better visual clues for genuine Ojuela material, but it is not a certificate. Look for the full Ojuela look: olive to apple-green botryoidal mimetite on rusty limonite, orange to amber wulfenite in blocky, tabular, prismatic, or pyramidal habits, and a vuggy gossan matrix. Compare questionable pieces with well-documented examples from Mindat, Wikimedia Commons, established dealers, and museum-grade auction archives.
Condition is a major value driver. Mimetite has Mohs hardness around 3.5–4 and is brittle; wulfenite is softer and often more exposed. On Ojuela combinations, the wulfenite crystals are commonly the first points of damage. Check for missing wulfenite tips, bruised edges on mimetite balls, flattened display surfaces from pocket contact, glued matrix repairs, and old trimming scars. Some limonite matrices are crumbly, so a specimen that looks solid in a photograph may still need careful handling.
Avoid overcleaning. The iron-rich matrix is part of the locality character, and aggressive chemical cleaning can weaken gossan, dull microcrystalline surfaces, or make a natural piece look suspiciously processed. Water, acids, and ultrasonic cleaning are poor choices for many Ojuela specimens unless the exact minerals and stability are known.
Market availability is good but uneven. Small green mimetite specimens and wulfenite-on-mimetite miniatures appear regularly from older collections and dealer inventories. Truly fine pieces—rich green color, large size, sharp wulfenite, minimal damage—are much scarcer and have become less common than casual market frequency suggests. Older orange-yellow mimetite, especially with strong hemispherical aggregates, is also worth watching because it represents a somewhat different Ojuela style from the more familiar green-wulfenite combinations of the 2000s.
In the old literature, Ojuela is not described as a tidy mine but as a subterranean world. Mary E. Mrose, Dan E. Mayers, and Francis A. Wise wrote that one could spend weeks underground there without revisiting the same spot. That line captures the scale of the place better than any production table: caves, pipes, stopes, shafts, and replacement bodies wandering through limestone, with oxidized ore pockets hidden far from daylight.
The most vivid collector story from Ojuela begins in June 1946, not with mimetite as the prize but with green mimetite as part of the lure. Mayers and Wise were on their way to a stope containing fine wulfenite and green mimetite when their lamps found something else in a small manway of the Las Palomas ore body, just above the 11th level. In the limestone wall was a pocket about four feet across and four feet deep. Its interior was carved into fantastic shapes and completely lined with undulating waves of sparkling yellow adamite crystals. The authors called it “a miniature grotto” and described the sight as a mineral specimen of unimaginable splendor.
They immediately set miners to work. The largest specimen from the pocket weighed 75 pounds underground and was nearly three feet square. It carried a continuous crust of green crystals, about one-quarter inch in size, on brown limonite. After trimming, that great plate went to the U.S. National Museum; two other notable pieces went to Harvard. The story matters to mimetite collectors because it shows how Ojuela’s best specimens were found: not in orderly production, but in pockets discovered during practical underground movement through a vast oxidized system where wulfenite, green mimetite, adamite, and other arsenates could occur in neighboring zones.
The mine’s surface story is just as memorable. The Ojuela settlement grew on the mountain near the mine entrance so workers could live close to the workings. By the late nineteenth century it had the services of a real mining town—church, post office, warehouses, stores, and saloons. The great suspension bridge, completed in 1898, carried people and material across the ravine. Modern accounts give the span as 271.5 meters between the main supports, and Spanish-language local histories describe the bridge as more than 300 meters long, less than two meters wide, and suspended above a drop of roughly 180 meters. Today that bridge is one of the surviving icons of the district, a reminder that every small green mimetite ball on a limonite matrix is connected to a much larger human landscape of railroads, smelters, flooded workings, old cooperatives, and desert mining ruins.
The late twentieth- and early twenty-first-century wulfenite finds added another chapter. For much of its specimen-producing life, Ojuela was better known for mimetite, adamite, and legrandite than for wulfenite. Then miners and collectors working the old Mapimí-area workings recovered striking orange wulfenites, many growing with and on dark green mimetite. Hundreds of specimens reached the collector market from these episodes, including the distinctive green mimetite–orange wulfenite combinations that now define Ojuela for many newer collectors.
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