The Mexican Minerals 6: Jalpaite

Abstract

Our country has long been renowned, and continues to be so, for its silver wealth. Most of its deposits are located in volcanic terrains. It is hardly surprising, then, to find within its mineralogy the entire range of argentiferous minerals, primarily sulfides. Among these are exquisite crystalline specimens of recognized universal standing: ubiquitous species that serve as milestones in mineralogical systematics.

Yet, importance also lies in those minerals which, as interstitials, occupy a prominent place within systematic lineages: they explain the chemical and crystallographic relationships between species, as well as the cleavage and merging of groups. Among these is our JALPAITE.

Closely related to argentite, it is distinguished by the isomorphous substitution of part of its silver for copper—a quality that separates it from its own group to politically enter that of stromeyerite. A similar emancipation is seen in another national mineral, aguilarite, through analogous transactions involving selenium.

Specimens of jalpaite recorded in mineralogical collections are rare; however, one should perhaps not conclude that it is an exotic species. It ought to be abundant, whether crystallized or in massive form, among argentite deposits located in cupriferous terrains, although its resemblance to the latter may have prevented its identification during mining operations. Stopes in metalliferous deposits are drastic, and the miner—lacking scientific interest and time for contemplation—clears away everything that resembles the ore.

Researchers have harbored many doubts regarding the individualization of jalpaite. It is part of the Ag-Cu-S ternary system as its alpha phase; however, without discontinuities in its transformation curves, it is rarely found isolated from other components. It usually occurs in intergrowth with them in mineral masses, and even when dominant in crystallized forms, it adopts the external habit of argentite crystals. Hence the doubts surrounding its diagnosis. Another mineral species with similar behavior also belongs to this system and was likewise discovered in Mexico, though it is less well-known: cocinerite.

Abstract from:

Gómez-Caballero, J. A. (2005). Historia e índice comentado del Boletín del Instituto de Geología de la UNAM. Boletín de la Sociedad Geológica Mexicana: Volumen Conmemorativo del Centenario Aspectos históricos de la Geología Mexicana, 57I(2), 149-185. http://dx.doi.org/10.18268/BSGM2005v57n2a3