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(searched for: doi:10.3390/min9120779)
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, Shaunna M. Morrison, Sergey V. Krivovichev, Robert T. Downs
American Mineralogist, Volume 107, pp 1288-1301; https://doi.org/10.2138/am-2022-8105

Abstract:
How does one best subdivide nature into kinds? All classification systems require rules for lumping similar objects into the same category, while splitting differing objects into separate categories. Mineralogical classification systems are no exception. Our work in placing mineral species within their evolutionary contexts necessitates this lumping and splitting because we classify “mineral natural kinds” based on unique combinations of formational environments and continuous temperature-pressure-composition phase space. Consequently, we lump two minerals into a single natural kind only if they: (1) are part of a continuous solid solution; (2) are isostructural or members of a homologous series; and (3) form by the same process. A systematic survey based on these criteria suggests that 2310 (~41%) of 5659 IMA-approved mineral species can be lumped with one or more other mineral species, corresponding to 667 “root mineral kinds,” of which 353 lump pairs of mineral species, while 129 lump three species. Eight mineral groups, including cancrinite, eudialyte, hornblende, jahnsite, labuntsovite, satorite, tetradymite, and tourmaline, are represented by 20 or more lumped IMA-approved mineral species. A list of 5659 IMA-approved mineral species corresponds to 4016 root mineral kinds according to these lumping criteria. The evolutionary system of mineral classification assigns an IMA-approved mineral species to two or more mineral natural kinds under either of two splitting criteria: (1) if it forms in two or more distinct paragenetic environments, or (2) if cluster analysis of the attributes of numerous specimens reveals more than one discrete combination of chemical and physical attributes. A total of 2310 IMA-approved species are known to form by two or more paragenetic processes and thus correspond to multiple mineral natural kinds; however, adequate data resources are not yet in hand to perform cluster analysis on more than a handful of mineral species. We find that 1623 IMA-approved species (~29%) correspond exactly to mineral natural kinds; i.e., they are known from only one paragenetic environment and are not lumped with another species in our evolutionary classification. Greater complexity is associated with 587 IMA-approved species that are both lumped with one or more other species and occur in two or more paragenetic environments. In these instances, identification of mineral natural kinds may involve both lumping and splitting of the corresponding IMA-approved species on the basis of multiple criteria. Based on the numbers of root mineral kinds, their known varied modes of formation, and predictions of minerals that occur on Earth but are as yet undiscovered and described, we estimate that Earth holds more than 10 000 mineral natural kinds.
Published: 15 February 2021
by MDPI
Abstract:
A suite of sulfate minerals from the Monte Arsiccio mine (Apuan Alps, Northern Tuscany, Italy), previously identified by using both X-ray diffraction and micro-Raman spectroscopy, was studied through inductively coupled plasma mass spectrometry (ICP-MS), in order to determine their trace-element content. Several elements (Tl, Rb, As, Sb, Co, Ni, Cu, Zn, and Cr) were found above the detection limits. Among them, some are important from an environmental perspective and may reach relatively high concentrations (e.g., Tl = 1370–2988 μg/g; As = 505–1680 μg/g). Thus, these sulfates may act as transient sinks for some of these potentially toxic elements, as well as for sulfate ions and acidity. Indeed, dissolution experiments revealed the ability of these secondary minerals to produce a significant pH decrease of the solutions, as well as the release of Fe, Al, and K as major ions. This work discusses the relation between the budget of trace elements and the crystal chemistry of sulfate minerals and provides new insights about the environmental role played by the sulfate dissolution in controlling the quality of water in acid mine drainage systems.
Published: 5 December 2020
by MDPI
Abstract:
The occurrence of sulfate minerals associated with the pyrite ores of the southern Apuan Alps has been known since the 19th century but modern mineralogical studies started only in the last decade. Sulfate assemblages were identified in all the pyrite ore deposits from the studied area but the more impressive associations were discovered in the Fornovolasco and Monte Arsiccio mines. Their study allowed to improve the knowledge of the sulfate crystal-chemistry and to achieve a better understanding of the acid mine drainage (AMD) systems associated with pyrite oxidation. More than 20 different mineral species were identified and, among them, four sulfates (volaschioite, giacovazzoite, magnanelliite, and scordariite) have their type localities in the pyrite ore deposits of the Apuan Alps. A review of the mineralogical results of a ten-year-long study is given here.
, Cristian Biagioni, Marco Pasero, Federica Zaccarini
Published: 30 June 2020
Mineralogical Magazine, Volume 84, pp 540-546; https://doi.org/10.1180/mgm.2020.51

Abstract:
Khademite, ideally Al(SO4)F(H2O)5, from the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy, has been characterised through quantitative electron microprobe analysis, micro-Raman spectroscopy and single-crystal X-ray diffraction. Khademite occurs as colourless to whitish tabular crystals, up to 5 mm. Electron microprobe analysis (in wt.%, average of 20 spot analyses) gave: SO3 35.43, Al2O3 21.27, F 6.92, H2Ocalc 39.73, sum 103.35, –O = F 2.92, total 100.43. On the basis of 10 anions per formula unit, assuming the occurrence of 5 H2O groups and 1 (F+OH) atom per formula unit, its chemical formula can be written as Al0.96S1.02O4[F0.84(OH)0.16]Σ1.00⋅5H2O. The Raman spectrum of khademite is characterised by the occurrence of vibrational modes of SO4 groups and by broad and strong bands due to the O–H stretching modes. Khademite is orthorhombic, space group Pcab, with unit-cell parameters a = 11.1713(2), b = 13.0432(3), c = 10.8815(2) Å, V = 1585.54(5) Å3 and Z = 8. The crystal structure refinement converged to R1 = 0.0293 on the basis of 2359 unique reflections with Fo > 4σ(Fo) and 152 refined parameters. The crystal structure of khademite is characterised by the alternation, along b, of two distinct kinds of {010} layers, one formed by [001] rows of isolated Al-centred octahedra, connected to each other through H bonds, and the other showing isolated SO4 groups. Along b, oxygen atoms belonging to SO4 groups act as acceptor of H bonds from H2O groups coordinating Al atoms. The new data improved the description of the H bonds in khademite and led us to discuss about the possible existence of its (OH)-analogue, rostite. In addition, Raman spectroscopic data were collected on the same crystal used for the crystal-chemical characterisation, allowing a comparison with previous results.
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