Ojuela mine, The

Ojuelaite ZnFe^sup 3+^^sub 2^(AsO^sub 4^)^sub 2^(OH)^sub 2^[middot]4H^sub 2^O

A find in the early 1970's in the legrandite zone in Palomes Oriente produced a small number of acicular yellow crystals of a then-unknown species that would later be named ojuelaite. The discovery yielded a few crystals to 2.5 cm lying flat on gossan matrix (Mike New, personal communication, 2002). As with the other unknown species recovered in that find (later named mapimite), those specimens were mostly lost and/or destroyed during incon-clusive testing.

Ojuelaite (with mapimite) was first described formally from the Ojuela mine in 1981 by Cesbron et al.; the type specimens also came from Palomas Oriente. The species occurs as flexible, chartreuse-colored, silky to vitreous monoclinic fibers to 4 mm, elongated parallel to [001], in some cases as felted masses lining legrandite pockets. The crystals usually occur in divergent sprays on goethite, associated with scorodite, smithsonite, paradamite and mapimite (Cesbron el at., 1981; Panczner, 1987); a good cleavage exists on {010}. Although the Ojuela mine remains the only known occurrence of mapimite, ojuelaite has since been found at Tsumeb, Namibia; Pitiquito, Sonora, Mexico; and the Sterling Hill mine, Ogdensburg, New Jersey.

Paradamite Zn^sub 2^(AsO^sub 4^)(OH)

Paradamite was described from the Ojuela mine in 1956, from a suite of secondary minerals in which the paradamite was associated with adamite, mimetite and legrandite in goethite vugs (Switzer, 1956). The original specimens were collected by George Griffith of Gomez Palacio, then sold to George Burnham of California before finding their way to the Smithsonian to be characterized as a new species (Switzer, 1956). Paradamite is the triclinic dimorph of orthorhombic adamite; according to Johnson (1962), it can form as a paramorphic pseudomorph after adamite as well. It is found as lustrous pale to medium-yellow, sheaflike crystal aggregates and equant, striated individual crystals with adamite and mimetite on goethite (Johnson, 1962). Although a few spectacular specimens have been found, paradamite remains an extremely rare mineral in the Ojuela mine, particularly in contrast to the abundant adamite which it so closely resembles. Panczner (1987) mentions paradamite crystals to 3 cm from the Ojuela mine, and White (1971) reports an "exciting new find" of paradamite appearing on the market in the early 1970's, with about 30 specimens showing up at the Tucson Show. The best Ojuela paradamite specimen is certainly the one in the Miguel Romero collection at the University of Arizona: a 6.7-cm goethite matrix almost entirely covered with large, sharp, lustrous, intergrown paradamite crystals of a rich yellow color (Wallace, 1999). Curt Van Scriver bought this piece from Salvador Davila for one dollar-both buyer and seller thought it was adamite.

As in the case of legrandite, Mexican specimens of paradamite went completely unrivaled in the world until the early 1990's, when the so-called "Zinc Pocket" in the lowest levels of the Tsumeb mine produced four exceptional paradamite specimens (translucent, cream-colored, 1-cm crystals in clusters on matrix to 8 cm), just before the mine's final closure (Gebhard, 1999).