A contribution to the mineralogy of the Larderello geothermal field. X-ray crystallographic studies on borate minerals "bechilite" and "lagonite" and crystal structure determination of ginorite

This work reports the results of mineralogical studies on some borate minerals from the Larderello geothermal field. XRD patterns of “bechilite” and “lagonite” confirmed they actually are respectively admixtures of sassolite and ammonioborite, and of sassolite with minor santite, gypsum and larderellite. Single crystal structural study of ginorite from the type locality, Sasso Pisano (Castelnuovo val di Cecina, Pisa) confirmed its isotypism with strontioginorite. Ginorite is monoclinic, space group P21/a, with unit cell parameters a =12.7673(1) Å, b = 14.3112(11), c = 12.7298(9), β= 101.055(5)° V=2282.8(2) Å3. The refinement of its crystal structure converged to R1 = 0.058 on the basis of 3387 reflections with Fo > 4σ (Fo). Analogously to strontioginorite, ginorite crystal structure can be described in terms of complex “sheets” parallel to (010), made up by borate groups and Ca coordination polyhedra, with interlayer linkage assured by Ca cations and hydrogen bonds. The cell volume contraction of ginorite respect to strontioginorite is related to the shrinkage of Ca coordination polyhedra present in the complex Me-borate sheets

Heliophyllite: a discredited mineral species identical to ecdemite

Abstract. The type material for heliophyllite, preserved in the Swedish Museum of Natural History in Stockholm, was re-investigated through a combined EPMA (electron probe X-ray microanalysis), Raman, and X-ray powder diffraction (XRPD) and single-crystal study. EPMA chemical data, together with Raman and single-crystal structural studies, point to heliophyllite being identical to ecdemite. XRPD synchrotron data highlight the presence of a minor quantity of finely admixed finnemanite in the analyzed material, explaining the presence of some additional diffraction peaks, not indexable with the ecdemite unit cell, reported in the literature. The discreditation of heliophyllite has been approved by the IMA Commission on New Minerals and Mineral Names (proposal 19-H, 2019)

Derbylite and graeserite from the Monte Arsiccio mine (Apuan Alps, Tuscany, Italy): occurrence and crystal-chemistry

New occurrences of derbylite, Fe2+xFe3+4-2xTi4+3+xSb3+O13(OH), and graeserite, Fe2+xFe3+4-2xTi4+3+xAs3+O13(OH), have been identified in the Monte Arsiccio mine, Apuan Alps (Tuscany, Italy). Derbylite occurs as prismatic to acicular black crystals in carbonate veins.Iron and Ti are replaced by V (up to 0.29 atoms per formula unit, apfu) and minor Cr (up to0.4 apfu). Mössbauer spectroscopy confirmed the occurrence of Fe 2+ (up to 0.73 apfu), along with Fe 3+ . The Sb/(As+Sb) atomic ratio range between 0.73 and 0.82. Minor Ba and Pb (up to 0.04 apfu) occur. Derbylite is monoclinic, space group P21/m, with unit-cell parameters a 7.1690(3), b 14.3515(7), c 4.9867(2) Å, β 104.820(3)°, V 495.99(4) Å 3 . The crystal structure was refined to R1 = 0.0352 for 1955 reflections with Fo > 4σ(Fo). Graeserite occurs as prismatic to tabular black crystals, usually twinned, in carbonate veins or as as porphyroblasts in schist. Graeserite in the first kind of assemblage is V-rich (up to 0.66 apfu), whereas it is V-poor in the second one (0.03 apfu). Along with minor Cr (up to 0.06 apfu), this element replaces Fe and Ti. The occurrence of Fe 2+ (up to 0.68 apfu) is confirmed by Mössbauer spectroscopy. Arsenic is dominant over Sb and detectable amounts of Ba and Pb have been measured (up to 0.27 apfu). Graeserite is monoclinic, space group C2/m. Unit-cell parameters are a 5.0225(7), b 14.3114(18), c 7.1743(9) Å, β 104.878(3)°, V 498.39(11) Å 3 and a 5.0275(4), b 14.2668(11), c 7.1663(5) Å, β 105.123(4)°, V 496.21(7) Å3 . The crystal structures of two graeserite samples were refined to R1 = 0.0399 and 0.0237 for 428 and 1081 reflections with Fo > 4σ(Fo), respectively. Derbylite and graeserite have homeotypic relations. They share the same tunnel structure, characterized by an octahedral framework and cuboctahedral cavities, hosting (As/Sb)O3 groups and (Ba/Pb) atom

XRF analysis of major and minor elements in silicate rocks using fused glass discs at high dilution ratio

XRF analysis of major and minor elements in silicate rocks using fused glass discs at high dilution ratio. X-ray fluorescence (XRF) is an accurate, rapid spectroscopic technique for chemical element determinations on rock samples. The aim of this research was to evaluate a calibration method for the determination of major and minor elements (Na, Mg, Al, Si, P, K, Ca, Ti, Mn, Fe) in silicate rocks using fused glass discs with a 1:30 sample/borate dilution. The analytical method has been calibrated by using forty-two international rock standards. The accuracy appears acceptable for many mineralogical and petrographic purposes. A high dilution ratio makes possible the use of a small amount of sample (225 mg) to obtain good castings in high-melting materials. By contrast, the decrease of the analytical intensity makes not easy the determination of trace elements at the typical concentration levels of geological samples

Palaeo-environmental reconstruction of the Mercure Basin (Basilicata region) during MIS 13, through a multi-proxy analysis of lacustrine sediments

The main purpose of this work is to make a first evaluation of the potential of the carbonate lacustrine sediment of the Mercure Basin (Basilicata region), to preserve palaeoclimatic information during the Middle Pleistocene. For this purpose a multi-proxy analysis of the lacustrine sediments from a selected section of the basin was undertaken. The selected section contains several tephra layers, which constrains the timing of deposition to MIS 13. Stable isotopes (oxygen and carbon) and element content were tentatively interpreted as linked to climatic changes giving interesting results for this poorly studied interval

The crystal structure of mineral fibres. 2. Amosite and fibrous anthophyllite

This study reports for the first time crystal-structure data for amosite and fibrous anthophyllite. The chemical composition of the two fibre species was determined from EMPA. Crystal structures were refined using powder-diffraction data, using both laboratory sources and synchrotron radiation. Results were compared with the available literature data for the non-fibrous varieties grunerite and anthophyllite, respectively. The calculated site-occupancies for all samples are in agreement with the chemical compositions calculated from EMPA. The existing structure models of grunerite and orthorhombic anthophyllite also applies to the corresponding fibrous varieties amosite and fibrous anthophyllite, respectively. In amosite, both Fe2+ and Fe3+ atoms are found at the sites M(1), M(2) and M(3) and Fe2+ ions is the only atomic species found at site M(4). Mg is disordered over the C sites with a preference for site M(2). Minor Ca and Na have been assigned to the A site. In fibrous anthophyllite, Mg is the only atomic species found at the M1, M2 and M3 sites. Fe2+, Mg (and minor Mn) have been assigned to the M4 site, whereas minor Ca has been assigned to the A site. In both structures, the environment at the M(4) site in amosite and M4 site in fibrous anthophyllite is highly distorted. This work can be considered a basis for studies aimed at understanding the potential toxicity/ pathogenicity of these mineral fibres

Effects of organic removal techniques prior to carbonate stable isotope analysis of lacustrine marls: a case study from palaeo‐lake Fucino (central Italy)

Rationale The suitability of organic matter (OM) removal pre‐treatments in isotopic studies of lacustrine carbonates is currently under debate. Naturally occurring OM seems to have a negligible effect on the bulk isotopic composition of carbonates compared with changes induced by pre‐treatments. This study provides further insights into the possible effects induced by commonly used pre‐treatments on natural lacustrine carbonates. Methods Sixteen samples from the Fucino F1–F3 lacustrine succession (Abruzzo, central Italy) were characterised for their mineralogical and geochemical composition and each was split into three identical aliquots. One aliquot was left untreated while the remaining two were treated with NaOCl and H2O2 dilutions. The same treatment was applied to an internal standard consisting of pure Carrara marble. The treated and untreated samples were analysed for their carbon (δ13C values) and oxygen (δ18O values) isotope compositions using an Analytical Precision AP2003 isotope ratio mass spectrometer. Results The samples had variable proportions of endogenic and detrital components, the detrital portion being more (less) abundant during colder (warmer) climate phases. We observed that neither the NaOCl nor the H2O2 treatment was able to completely remove OM and therefore there was selective removal of compounds within the OM pool. A possible effect of pre‐treatment is the loss of carbonates intimately interspersed within the OM, as suggested by the evolution of isotopic ratios towards the local detrital array. Conclusions Our study highlights sample‐specific changes in geochemistry associated with sample pre‐treatments; however, such changes do not seem to lead to either systematic and/or predictable isotopic shifts. We suggest that the suitability of NaOCl or H2O2 pre‐treatments for OM removal should be evaluated on a case‐by‐case basis. In the specific case of lacustrine marls from palaeo‐lake Fucino containing relatively low amounts of OM and in which both detrital and endogenic carbonates occur, both pre‐treatments should be avoided

Crystal structure study of a cobaltoan dolomite from Kolwezi, Democratic Republic of Congo

A structural study has been undertaken on a cobaltoan dolomite, with chemical formula CaMg0.83Co0.17(CO3)2 (calcium magnesium cobalt dicarbonate), from Kolwezi, Democratic Republic of Congo. Pale-pink euhedral cobaltoan dolomite was associated with kolwezite [(Cu1.33Co0.67)(CO3)(OH)2] and cobaltoan malachite [(Cu,Co)2(CO3)(OH)2]. A crystal with a Co:Mg ratio of 1:5.6 (SEM/EDAX measurement), twinned on (11 -2 0) was used for crystal structural refinement. The refinement of the structural model of Reeder & Wenk [Am. Mineral. (1983), 68, 769–776; Ca at site 3a with site symmetry -3; Mg site at site 3b with site symmetry -3; C at site 6c with site symmetry 3; O at site 18f with site symmetry 1] showed that Co is totally incorporated in the Mg site, with refined occupancy Mg0.83Co0.17, which compares with Mg0.85Co0.15 from chemical data. The Co substitution reflects in the expansion of the cell volume, with a pronounced increasing of the c cell parameter