1,721,119 research outputs found
Crystal structure determination and Rietveld refinement of rosasite and mcguinnessite
No full textThe crystal structure of rosasite, (Cu, Zn)(2)(CO3)(OH)(2), and mcguinnessite, (Mg,Cu)(2)(CO3)(OH)(2) have been determined from powder data. The two minerals are isostructural, with space group P2(1)/a and cell constants a=12.8976(3), b=9.3705(1), c=3.1623(1) angstrom, beta=110.262(3)degrees, V =358.54(2) angstrom(3), for rosasite and a=12.9181(4), b=9.3923(2), c=3.1622(1) angstrom, beta=111.233(3)degrees, V=357.63(2) angstrom(3) for mcguinnessite. The crystal structure refinements were lead up to R-p =7.51%, wR(p)=10.39% for rosasite and R-p =5.12%, wR(p)=6.22% for mcguinnessite. In both the two structures, the Cu coordination octahedron is distorted towards an elongated tetragonal bipyramid, whereas the Zn (in rosasite) and Mg (in mcguinnessite) coordination octahedra display an almost regular shape, their distortion being due to a partial occupancy of Cu. The carbonate group was refined as a rigid body, with a regular triangular geometry. Metal coordination octahedra polymerize through edge sharing to form octahedral "columns" and "ribbons", running along [001] and responsible for the acicular habit of these minerals. The structural relationships between rosasite and malachite are discussed
Attività della sezione di mineralogia del Museo di Storia Naturale e del Territorio dell'Università di Pisa.
No full text
Crystal structure study of a cobaltoan dolomite from Kolwezi, Democratic Republic of Congo
Full text linkA 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
CHEMICAL, MINERALOGICAL AND PETROGRAPHIC ANALYSES ON EXPANSIBLE BLAST-FURNACE SLAG USED AS A FOUNDATION MATERIAL IN THE IV MODULE OF THE GENOVA-VOLTRI PORT (ITALY)
No full textAfter the construction of the paving for container storage in the Genova-Voltri port, considerable ground swellings (up to 30 cm) took place, leading to dimensional damage of both crane runways and loading/unloading area, including the container ground slots. This is due to expansible chemical reactions occurred within blast-furnace slags employed as a foundation material. The aim of this study was that to determine the chemical and mineralogical characteristics of blast-furnace slag and to identify the phases that are expected to be responsible for expansible chemical reactions. For this purpose, materials from three geognostic drillings 20m deep were analyzed and their stratigraphic sequence reconstructed.
The study of the drillings (from 0 to 3m deep) led to a full characterization of the foundation materials used for building the IV module in the port of Genoa-Voltri. The present study revealed the presence of a complex stratigraphy, with layers indicating the presence of metallurgical slag. The slag-rich layers are present at varying depths in the various surveys and their average thickness is about 90cm in the three examined ones.
Thin section study, X-ray powder diffraction, scanning electron microscopy observations and microanalyses of some selected samples allowed to identify the presence of chrysotile and of the phases commonly described in the metallurgic slag.
The chemical and mineralogical data showed the presence of anhydrous phases: merwinite (3CaO MgO 2SiO2), olivina 2(MgO, FeO) SiO2, alite C3S (3CaO SiO2), belite C2S (2CaO SiO2), ferrite phase C4AF (4CaO Al2O3 Fe2O3), lime CaO, periclase MgO, wuestite FeO and a phase with intermediate composition FeO-MnO-MgO. Hydrated phases such as brucite, portlandite, gibbsite, goethite, and products of hydration of the cement phases have been also identified by XRPD and TG/DSC analyses.
The formation of these hydrated phases caused a significant volumetric instability, mainly due to the presence of free CaO and free MgO, which in the presence of water form portlandite, Ca(OH)2 and brucite, Mg(OH)2.
According to literature studies, the hydration reaction of free lime can lead in few days to a volume increase up to 100%. Hydration reaction of free periclase is instead slower, leading to considerable volume increase even after months or years. Therefore, it is not possible to exclude that in the next future relevant swelling phenomena should occur again
THE CRYSTAL-STRUCTURE OF HIORTDAHLITE-II
No full textThe crystal structure of Hiortdahlite II [triclinic P1, a = 11.012(6), b = 10.342(3), c = 7.359 (3) Å, a = 89.92(2)°, β = 109.21(5)°, y = 90.06(3)°], was determined and refined using 1793 reflections to R1 = 0.069 and R2 = 0.066. The results of the structural study indicated that hiortdahlite II presents the modules which characterize the whole family of minerals related to cuspidine and låvenite, namely "octahedral walls", four columns large and running along c, and Si2O7 groups. In hiortdahlite II the modules are connected according to the same topology realized in låvenite. The peculiar octahedral cations distribution, which is determined and discussed in this work, is responsible for the descent in symmetry to P
Modular mineralogy in the cuspidine group of minerals
No full textThe crystal structures of the minerals in the cuspidine-wohleritc- lavenite group can be described in terms of two kinds of modules whose connections form the structures of the various phases: "octahedral walls" four columns wide and running along c, and diorthosilicate groups. The octahedral walls are interconnected by corner sharing to create a framework that is the common feature in all the structuresof the family. There are various waysto distrib ute the Si207 units, whichserveto strengthen the frame work. Ten different structure-types were derived, within
fixed cell dimensions (a = b = 10.5 A, c = 7.3 A). One of these structure-types, with topological symmetry P21/a, is shown by cuspidine and lavenite, both with space-group symmetry Pl^/a, as well as by niocalite, in which the space-group symmetryis lowered to Pa by the ordering of the octahedral cations. Another structure-type, with topological symmetry P-l, is shown by wohlerite.The enumeration of the possible structure-types wassuccessfully applied to determine the unknown structures ofother natural phases in the group: hiortdahlite I and II, baghdadite, and a natural phase from the Burpala Massif, USSR. The disorder phenomena commonly occurring in these minerals, such as domain structure, micro-scale twinning, and stacking faults, can be interpreted on the basis of the "modular" structure
- …
