A crystallographic excursion in the extraordinary world of minerals: the case of Cu- and Ag-rich sulfosalts

Abstract

Copper and silver are common constituents in natural sulfosalts and can be present as minor or major components. Owing to the different kinds of coordination they can assume, these elements give rise to a number of sulfosalts that are usually quite complex to describe from a structural point of view because of the presence of twinning, disorder, polytypism and sometimes incommensurate modulation. Moreover, it is common to find them in different, partially occupied split sites, favoring the presence of strong ionic conductivity that can be related to a number of interesting technological properties. In this regard, a series of Cu-and Ag-rich sulfosalts showing an excess of these cations with respect to As, Sb and Bi is particularly interesting. Their crystal structures as well as their potential interest for materials science and solid-state physics are outlined. Copper-and mixed (Cu, Ag)-sulfosalts belonging to the wittichenite, tetrahedrite, galkhaite, routhierite and nowackiite series are discussed, together with some related compounds. Whereas in the wittichenite series Cu has either a trigonal planar or tetrahedral coordination, in members of the other series this element forms three-dimensional tetrahedral frameworks giving rise to cavities hosting other cations and anions. More difficult is the description of Ag-rich sulfosalts owing to the highly variable coordination environments shown by this element. Structural features of selected Ag sulfosalts together with members of the argyrodite series are discussed, highlighting the particular properties derived from the behavior of Ag.

Copper Minerals at Vesuvius Volcano (Southern Italy): A Mineralogical Review

“…The chemical composition of the fumaroles of the crater bottom relate to the hydrothermal type, with the typical presence of H 2 S [14]. According to Chiodini et al [14], CH 4 and NH 3 contents suggest that the origin of these fluids is related to a high-temperature hydrothermal system located underneath the Vesuvius crater area. These authors argued that NaCl brines reside in the high-temperature reservoir and have an influence on the chemical composition of the gases discharged by the fumaroles of the crater bottom.…”

“…As a transition metal, Cu is moderately siderophile and strongly chalcophile, with approximately two thirds of terrestrial Cu thought to be stored in the core [3]. In the silicate Earth, it behaves as a chalcophile element and usually forms stable sulfides, among which chalcopyrite (CuFeS 2 ) is the most common Cu-bearing mineral; copper is also a common constituent, together with silver, in natural sulfosalts [4]. However, in nature, copper occurs in a great variety of minerals; according to the mindat.org database [5], it is essentially contained in 562 valid mineral species, in decreasing order of abundance, hosted in sulfides-sulfosalts, phosphates-arseniates-vanadates, sulfates, oxides, halides, silicates, carbonates, borates and native elements.…”

Tellurium Minerals: Structural and Chemical Diversity and Complexity

“…Tellurium minerals are relatively rare, and, currently, only 176 mineral species are known [40] ( Supplementary Table S1). In minerals, Te participates in various forms of intermetallic bonding in tellurides [41][42][43], e.g., in hessite and calaverite [44]. In O-bearing species, tellurium occurs as Te 4+ and/or Te 6+ cations.…”

Progress in the knowledge of ‘ruby silvers’: New structural and chemical data of pyrostilpnite, Ag3SbS3

“…In the framework of a systematic study of silver sulfosalts (e.g. Bindi and Biagioni, 2018), a new crystallographic investigation of this mineral was performed, improving the quality of the available structural data.…”