Ojuela
Mexico's classic oxidised deposit, known worldwide for hemimorphite, adamite and legendary arsenate species on limonite.
The Ojuela Mine at Mapimí in Durango, Mexico has been worked since the 1500s and is one of the world's great oxidised orebodies. Ojuela is the benchmark locality for adamite and hemimorphite, and produces a superb arsenate suite — legrandite, paradamite, aurichalcite and wulfenite — almost always on the warm brown limonite matrix that makes an Ojuela specimen recognisable across a room.
In short
- Worked since the 1500s; the deep oxidised zone is what collectors want.
- The world benchmark for adamite and hemimorphite.
- Legrandite from Ojuela is among the most valuable specimens on earth.
- The warm brown limonite matrix is instantly recognisable.
- Still producing, unlike Tsumeb — supply continues, quality varies.
| Species | Character |
|---|---|
| Adamite | Yellow-green, often fluorescent; the classic |
| Hemimorphite | Blue botryoidal and colourless bladed |
| Legrandite | Golden yellow blades — genuinely world-class and expensive |
| Paradamite | Rare dimorph of adamite |
| Aurichalcite | Pale blue-green acicular tufts |
| Köttigite, wulfenite, calcite | Strong supporting cast |
Why the matrix matters
Ojuela specimens are usually mounted on a warm brown to ochre limonite gossan, and that matrix is part of the aesthetic. It sets off the yellow-green of adamite and the blue of hemimorphite in a way a pale matrix does not, and it makes the locality recognisable across a room.
It is also a caution: the matrix is fragile and friable. Handle by the base and store in a padded box.
Legrandite, and what world-class costs
Legrandite is a zinc arsenate that occurs in commercial quality essentially only here. The finest pieces — golden blades in radiating sprays — sit among the most valuable mineral specimens ever sold.
Ordinary legrandite exists too, and is a reasonable buy. As always the gap between good and great in a famous species is measured in multiples.
Still working
Unlike Tsumeb, Ojuela continues to yield specimens through small-scale local mining. That keeps material available but means quality and honesty vary by source.
Fresh adamite should fluoresce a strong green under longwave UV. It is a quick, useful check.