Scorodite from the Ojuela Mine is one of the quieter great prizes of the Mapimí district: not as instantly abundant in the marketplace as adamite, not as flamboyant as legrandite, but, in fine examples, a superb blue arsenate from one of Mexico’s most storied oxidized ore systems. The best pieces show glassy, sharply formed blue to blue-green scorodite crystals in pockets of dark brown goethite and limonite gossan, the color standing out with a wet, electric intensity against iron oxide matrix. Collectors prize Ojuela scorodite for that contrast, for the sharpness of the crystals, and for the mine’s long reputation as a classic source of secondary arsenates.
Photo: Wikimedia Commons
The geological reason is straightforward but unusually productive. Ojuela is a large limestone-replacement lead-silver system in the Sierra de Mapimí. Primary ore minerals such as arsenopyrite, pyrite, sphalerite, and argentiferous galena were emplaced in carbonate host rocks; later, deep oxidation converted parts of that sulfide system into a complex suite of secondary arsenates, sulfates, carbonates, oxides, and hydroxides. Scorodite, Fe3+AsO4·2H2O, is an iron arsenate of that oxidized environment, and at Ojuela it is most at home in small vugs and cavities in hard iron oxide matrix.
Historically, scorodite was never the bulk mineral that made Ojuela famous. Adamite did that, followed by legrandite and a cast of rare arsenates that made the mine a benchmark locality. Scorodite’s appeal lies partly in its selectiveness: good examples are uncommon, the finest pockets were few, and older Ojuela scorodite has long carried the aura of a specimen a seasoned collector recognizes across a room but may wait years to acquire. The key visual standard is crisp blue crystallization on honest Ojuela gossan—not merely a label from Mapimí, but the mineralogical look of the mine itself.
Search for specimens: View all scorodite specimens from Ojuela Mine, Mexico
The Ojuela Mine lies near Mapimí in Durango, on the northeastern side of the Sierra de Mapimí. It is best understood by collectors not as a single tidy opening but as a major mine complex, with named shafts, stopes, chimneys, collecting areas, and long-developed workings. Historical descriptions emphasize its enormous underground extent: one early account notes that a person could spend weeks underground without retracing the same route. That scale matters, because the specimen minerals did not come from one uniform ore body; they came from cavities, chimneys, mantos, dumps, and oxidized zones encountered across a large and complicated replacement system.
The deposit is a northern Mexican limestone-replacement ore body. Mineralization followed fractures and favorable dolomitic horizons, producing widely separated pipes and caves in limestone. The primary sulfide assemblage included arsenopyrite, pyrite, sphalerite, and silver-bearing galena, with calcite, quartz, fluorite, and limonite among the important gangue minerals. Subsequent oxidation generated the extraordinary secondary mineral suite for which Ojuela is known: adamite, legrandite, paradamite, ojuelaite, mapimite, lotharmeyerite, arseniosiderite, hemimorphite, wulfenite, mimetite, rosasite, aurichalcite, plattnerite, fluorite, calcite, and many others. Mindat currently records 149 valid minerals from the Ojuela locality and seven type-locality minerals, which gives a fair sense of the mine’s mineralogical density.
Mining history reaches back to the colonial period. The deposit is commonly described as having been discovered by Spanish prospectors in the late 16th century, with shallow workings for rich secondary silver ores underway by about 1600. In the late 19th century it became a major lead-silver property, and in 1893 the operation was modernized under the American Metals Company. Historical summaries record nearly four million tons of ore mined after that conversion, averaging 3.7 grams per tonne gold, 462 grams per tonne silver, and 14.9 percent lead. Large-scale production later declined under the combined pressure of drainage difficulties and reserve depletion, though small-scale mining and specimen recovery continued episodically.
For the modern visitor, Ojuela is also a heritage and tourism site. The famous suspension bridge, mine ruins, guided underground visits, and adventure activities have made the area a recognized destination near Mapimí. That should not be confused with open collector access. The mine is a historic, hazardous, and locally managed site; collecting underground or on dumps requires proper permission from the relevant land, mineral-rights, or site authorities. Most serious Ojuela specimens in collections and on the market have come through miners, permitted specimen work, old collections, dealers, and historical finds rather than casual public collecting.
For scorodite specifically, the important specimen history is discontinuous. Literature and later market reports indicate that scorodite microcrystals were known from Ojuela material as early as 1927, but the first truly notable macro-quality pieces were associated with later finds. The best-known classic production includes blue scorodite crystals in small vugs in compact goethite, with individuals reported to 2 cm. Later significant material appeared from the Los Changos collecting area in 2013, including sharp crystals to 2 cm that tended to be dark blue-black and opaque with pyrite spotting. A 2019 find, apparently from an unnamed area of the mine, produced cleaner, glassier crystals lining shallow vugs in hard dark brown goethite; these pieces were noted for sharpness, luster, transparency, and possible blue-to-green color response under different incident light.
Ojuela scorodite is most commonly encountered as sharp, blocky to pseudo-octahedral orthorhombic crystals lining vugs in iron oxide matrix. Fine pieces show lustrous, transparent to translucent crystals packed across the roof or floor of a shallow cavity, sometimes as isolated crystals, sometimes as crowded druses. The crystal shape is one of the pleasures of the locality: even when crystals are only a few millimeters across, they can be glassy, well individualized, and crisp enough to read under magnification.
The classic color is blue—ranging from pale watery blue to deep steel-blue, blue-black, and rich blue-green. Some crystals are so clear that the brown matrix beneath can influence their apparent color; others are dark and opaque, especially in pyrite-spotted material. Collectors should expect variation. Ojuela scorodite is not a uniform “neon blue” product; the locality’s best material combines blue color, strong luster, and transparency, while lesser pieces may be darker, browner, more silvery, or more granular.
Typical crystal size depends strongly on the find. Many specimens show crystals in the 2–7 mm range, which is already respectable for the locality when the crystals are sharp and attractive. Documented major finds produced individuals to about 2 cm, but such crystals are exceptional and command a different level of interest. Matrix sizes range from thumbnails and miniatures to small cabinets, with larger plates prized when the scorodite is both abundant and well exposed.
The matrix is usually limonitic to goethitic gossan: dark brown, reddish brown, blackish brown, porous, and cavernous. That iron oxide matrix is not incidental; it provides the visual stage for the blue crystals and also records the oxidized environment that made the mineral possible. Associated minerals documented with Ojuela scorodite include goethite, limonite, arsenopyrite, fluorite, arseniosiderite, beudantite, pyrite, adamite, pharmacosiderite, gypsum or selenite, woodruffite, and, more rarely in association records, native silver or native copper. Ojuelaite specimens have also been described with blue scorodite and legrandite, linking scorodite to the broader zinc-iron arsenate paragenesis of the mine.
Quality is judged by five main factors. First is color: rich blue or blue-green is preferred, especially when it remains attractive under normal display lighting. Second is luster: the finest crystals have a glassy flash rather than a dull or earthy surface. Third is crystal definition: sharp, separate, undamaged crystals are worth far more than granular coatings. Fourth is contrast: blue scorodite on dark brown gossan is the signature look. Fifth is provenance: old labels, connection to a known find, or documented collection history can significantly elevate an already good specimen.
The first authenticity issue with Ojuela scorodite is locality confidence. Ojuela is famous enough that many Mexican secondary-mineral specimens have been casually or incorrectly attributed to it. Mindat specifically warns that many minerals sold as Ojuela material are actually from other Mexican localities, and this caution is especially relevant for collectors buying from old mixed lots or vague “Mapimí” labels. With scorodite, confusion with other Mexican scorodite localities is a real concern; Zacatecas material in particular has circulated widely and can be visually more familiar to many collectors. A strong Ojuela attribution should be supported by old labels, reputable dealer history, collection provenance, or the characteristic association with Ojuela gossan and paragenesis.
No well-documented, locality-specific scorodite treatment scandal is established for Ojuela in the way that artificial blue hemimorphite and likely man-made kobyashevite have been documented for other Ojuela-labeled material. Still, the broader Ojuela market has enough misattribution and enhancement history that scrutiny is justified. Avoid pieces with suspiciously uniform artificial-looking color, vague locality wording, or an implausible association suite. For significant purchases, ask for provenance and compare the specimen against documented Ojuela examples.
Condition is a major value factor. Scorodite has modest hardness, and Ojuela crystals are often perched on rough gossan in exposed vugs, so edge chipping, bruising, contact points, and missing crystal tips are common. Some historical dealer descriptions explicitly note minor edge chipping as expected for the material. Use magnification: the difference between natural pocket contact and careless post-collection damage can be subtle but important. Friable matrix is also a concern; iron oxide gossan can shed grains, and over-cleaning may dull the surface or destabilize the specimen.
Because scorodite is an arsenate, treat it with sensible mineral-handling hygiene. Do not cut, grind, sand, heat, or acid-clean specimens. Wash hands after handling, keep dust away from children and pets, and store loose fragments carefully. Normal display of intact specimens is not a problem for responsible collectors, but aggressive cleaning is unnecessary and can damage both the mineral and its provenance.
Market availability is sporadic rather than steady. Small, lesser examples appear from time to time, but sharp blue Ojuela scorodite with good luster and attractive matrix remains a classic that disappears quickly when priced reasonably. Recent dealer and auction records show a broad range: modest old small-cabinet examples with small crystals may sell in the low hundreds, while stronger miniatures and small cabinets with rich blue, glassy crystals have been offered in the hundreds to low thousands. Top pieces with large, transparent, well-covered vugs and good provenance are much harder to replace than their size alone suggests.
Long before scorodite became a recognized prize from Ojuela, the mine itself had already acquired near-mythic scale in mineralogical writing. Mary E. Mrose’s 1948 paper on adamite included field notes by Dan E. Mayers and Francis A. Wise, and their description still reads like a dispatch from a vast underground city. Ojuela, they wrote, sat at the base of the northeastern escarpment of the Sierra de Mapimí, about five miles southeast of Mapimí, and was so extensive that “one may spend weeks travelling underground without revisiting the same spot.” That single sentence explains much about the locality: Ojuela is not a pocket locality in the small sense. It is a labyrinth, and its best specimens came from rare favorable spaces within that labyrinth.
The same 1948 account captures the specimen era beginning to take shape. In June 1946, Mayers and Wise were on their way to a stope containing good wulfenite and green mimetite when their lamps caught a pocket in limestone in the Las Palomas ore body, just above the 11th level. What they saw was not scorodite, but the discovery changed Ojuela’s collector history: a four-foot-wide, four-foot-deep adamite grotto whose interior was carved into “fantastic shapes” and coated with undulating waves of sparkling yellow crystals. The largest specimen weighed 75 pounds underground and was nearly three feet square before trimming. It went to the U.S. National Museum; two other notable pieces entered the Harvard collection. That story belongs to adamite, but it marks the moment when Ojuela emerged as more than an old ore mine. It became a specimen mine of world rank.
Scorodite’s own story is more elusive. By the time later writers compiled Ojuela’s mineral list for the major 2003 Mineralogical Record special issue, the literature indicated that scorodite microcrystals had been observed in Ojuela material as early as 1927. For decades, however, the species was not represented by the sort of specimens that define a locality. It was present, known, and mineralogically real, but not yet a collector’s target on the level of Ojuela’s celebrated arsenates.
Then came the classic blue material. The finest known Ojuela scorodites were described as found in 1981: excellent clusters of blue crystals, with individual crystals reaching 2 cm, sitting in small vugs in compact goethite. The best examples reportedly entered the Harvard collection. That is the kind of sentence that makes collectors pause, because it means the standard was set not by a steady commercial stream but by a limited discovery, with the premier pieces absorbed into an institutional collection.
The next important chapter did not arrive until May 2013, when Los Changos produced another significant scorodite occurrence. These specimens again reached crystals to 2 cm and were first marketed at the 2013 Denver Show. They were sharp but tended toward dark blue-black opacity, and pyrite spotting was noted as a characteristic. That find gave collectors a fresh chance at Ojuela scorodite, but it also broadened the visual range of what “good Ojuela scorodite” could mean: not just bright blue glass, but dark, sharp, iron-rich crystals from a very specific collecting area.
A still later find, seen in the market around 2019, brought a different look. At the 2019 Munich Show, about 20 miniatures were observed that matched later Weinrich Minerals pieces: shallow vugs in hard dark brown goethite lined with sharp, lustrous, clean, transparent scorodite crystals. The best crystals were under 1 cm, but they were crowded together lavishly, with blue contrasting against the iron oxide matrix. A color response from bright blue to bright green under changing incident light was also noted for material believed to be from this find. For a locality where decades can separate important scorodite appearances, those Munich and Weinrich pieces represented not just inventory but a new paragraph in Ojuela’s specimen history.
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