Ojuela / Mapimí minerals

Ask a mineral collector to name Mexico's greatest locality and most of them say Ojuela without pausing. The mine sits about five kilometres southeast of Mapimí in Durango, the Spanish found the deposit in 1598, and it was worked for roughly three hundred and fifty years for silver and lead before production and logistics finally made it uneconomic.

What came out along the way is why the name endures. Something over a hundred species are recorded from the deposit, and Ojuela holds the world standard for several of them. Adamite above all, in a range of colours and habits nowhere else matches, and legrandite, which is essentially an Ojuela mineral in the public imagination. Add köttigite, parasymplesite, paradamite, and superb scorodite, hemimorphite, plattnerite, aurichalcite, rosasite, fluorite, calcite and wulfenite. These are oxidation-zone minerals, secondary species grown in the weathered upper part of a sulphide orebody, which is exactly the environment that makes brilliantly coloured, well-formed crystals.

Then there is the approach, which is the reason people who do not care about minerals still come. The workings are on the far side of a canyon, and you cross it on the Ojuela suspension bridge, a little over three hundred metres of nineteenth-century engineering hung above a substantial drop. It is a designated historic structure and walking it is the whole trip for most visitors.

Be clear about what you can and cannot do here. Mapimí is set up for visitors and the bridge and the ghost-town workings are the local attraction, so going is straightforward. The underground is not a tourist mine, and specimen production has long been in the hands of local miners who work it and sell through dealers. Buy from them in the village. That is how Ojuela material has reached collectors for a century and it is still the right way to get a piece.