Papers by Francesco Princivalle
Alla fine del XIX secolo il francese E. A. Martel coniò il termine "speleologia" per definire la ... more Alla fine del XIX secolo il francese E. A. Martel coniò il termine "speleologia" per definire la scienza che ha come oggetto di studio le grotte, e nel 1883 a Trieste fu fondata la Società degli Alpinisti Triestini (dal 1886 Società Alpina delle Giulie), il primo gruppo speleologico al mondo. L'interesse per le moltissime cavità del Carso triestino s'intensificò conseguentemente, coinvolgendo anche alcuni personaggi -C. Marchesetti, soprattutto -che aprirono la strada alla ricerca archeologica sistematica.
International Journal of Earth Sciences, 2009
The Š ambron-Kamenica Zone is situated on the northern margin of the Levočské vrchy mountains and... more The Š ambron-Kamenica Zone is situated on the northern margin of the Levočské vrchy mountains and Š arišskà vrchovina Highland, where the Central Carpathian Paleogene joins the Pieniny Klippen Belt. Sandstone outcrops in this area. From Cretaceous to Late Oligocene in age, these sediments suggest transport directions from S and SE. The heavy mineral assemblages of this sandstone include Cr-spinel grains, mainly displaying types II and III alpine-peridotite affinities, and are representative of Ocean Island Basalt volcanism. A sample from Upper Eocene sediments at Vit'az shows a clear change in Cr-spinel composition, which turns out to have types I and II peridotite affinities, and to derive from arc and Middle Ocean Ridge Basalt volcanism, with sediment transport directions from SW and WSW. These data indicate major variations in the Upper Eocene tectonic setting, giving constraints to paleogeographic reconstruction of the Slovak Central Carpathians.
Physics and Chemistry of Minerals, 2006
The influence on the spinel structure of Fe 3+ fi Cr substitution was studied in flux-grown synth... more The influence on the spinel structure of Fe 3+ fi Cr substitution was studied in flux-grown synthetic single crystals of the magnesiochromitemagnesioferrite (MgCr 2 O 4 -MgFe 2 O 4 ) solid solution series. Samples were analysed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption and Mo¨ssbauer spectroscopy. With the exception of iron-poor samples (3-12 mol-% MgFe 2 O 4 ), optical absorption and Mo¨ssbauer spectra show that iron occurs almost exclusively as trivalent Fe in the present samples. A very intense and broad absorption band at ca 7,800 cm À1 dominates the optical absorption spectra of samples with higher Fe-contents. The appearance of this band is related to a distinct structural disorder of Fe 3+ and a development of magnetic ordering as demonstrated by Mo¨ssbauer spectra. Profound composition-related changes are observed in the Mo¨ssbauer spectra, which are magnetically unsplit in the range 2-41 mol-% magnesioferrite, but become magnetically split in the range 59-100 mol-% magnesioferrite. Structural parameters a 0 and M-O increase with magnesioferrite content and inversion degree, while u and T-O decrease. Our study confirms the previously reported influence of Fe 3+ at the M site on T-O bond lengths in the spinel structure.
Formulation and Evaluation of Vinylpyrrolidone/Vinylacetate Copolymer Microspheres with Carbamazepine
Pharmaceutical Development and Technology, 2000
Vinylpyrrolidone/vinylacetate copolymer (VP/VAc) was used for the enhancement of dissolution rate... more Vinylpyrrolidone/vinylacetate copolymer (VP/VAc) was used for the enhancement of dissolution rate of carbamazepine, an antiepileptic drug characterized by very low water solubility. Microspheres containing different drug-to-polymer ratios were prepared using a solvent-evaporation technique and their physical characterizations were carried out by differential scanning calorimetry, x-ray diffractometry, and scanning electron microscopy. Through the solubilization kinetics and dissolution rates studies, the in vitro drug availability of the microspheres was evaluated. These results showed that the dissolution of carbamazepine in gastrointestinal fluids from all of the prepared formulations was increased with respect to the drug itself. However, the best dissolution parameters were obtained from 1:10 w/w system because of the presence of the drug in amorphous form and its efficient encapsulation.
The effect of non-stoichiometry on the high-temperature behaviour of MgAl<SUB>2</SUB>O<SUB>4</SUB> spinel
Mineralogical Magazine, 2009
ABSTRACT The effect of cation vacancies upon the thermal expansion and crystal Structure of,I Syn... more ABSTRACT The effect of cation vacancies upon the thermal expansion and crystal Structure of,I Synthetic defect spinel with composition Mg0.4Al2.4 square O-0.2(4) was investigated by X-ray diffraction. in Win, at temperatures LIP 10 1273 K. No evidence of symmetry violations from the Fd (3) over barm even at the highest temperature were noted. The volume thermal expansion is markedly less than that of stoichiometric MgAl2O4 spinel, regardless of the degree of inversion. The u oxygen atomic coordinate remains constant throughout the temperature range investigated, with the M-O and T-O bond lengths showing identical rates of expansivities. An analysis of the evolution of polyhedral volumes with temperature indicates that at 1273 K the octahedron inflates by 0.099 angstrom(3) and the tetrahedron by 0.056 angstrom(3). The expansion of the octahedron is significantly greater than in stoichiometric MgAl2O4 spinel, whereas the expansion of the tetrahedron is similar. The results demonstrate that an excess of Al in the spinel structure accompanied by the formation of cation vacancies strongly affect in important thermodynamic property, in this case, thermal expansion. Such an effect Must be considered for those phases stable in the Earth&#39;s mantle where 4-5 wt% Al2O3 is thought to be present.
Geochimica et Cosmochimica Acta, 2009
A non-stoichiometric sample of spinel with composition T (Mg 0.4 Al 0.6 ) M (Al 1.8 h 0.2 )O 4 wa... more A non-stoichiometric sample of spinel with composition T (Mg 0.4 Al 0.6 ) M (Al 1.8 h 0.2 )O 4 was investigated by single-crystal X-ray diffraction in situ up to about 8.7 GPa using a diamond anvil cell. The P(V) data were fitted using a third-order Birch-Murnaghan equation of state and the unit-cell volume V 0 , the bulk modulus K T0 and its first pressure derivative K 0 were refined simultaneously providing the following coefficients: V 0 = 510.34(6) Å 3 , K T0 = 171(2) GPa, K 0 = 7.3(6). This K T0 value represents the lowest ever found for spinel crystal structures. Comparing our data with a stoichiometric and natural MgAl 2 O 4 (pure composition) we observe a decrease in K T0 by about 11.5% and a strong increase in K 0 by about 33%. These results demonstrate how an excess of Al accompanied by the formation of significant cation vacancies at octahedral site strongly affects the thermodynamic properties of spinel structure. If we consider that the estimated mantle composition is characterized by 3-5% of Al 2 O 3 this could imply an Mg/Al substitution with possible formation of cation vacancies. The results of our study indicate that geodynamic models should take into account the potential effect of Mg/Al substitution on the incompressibility of the main mantle-forming minerals (olivine, wadsleyite, ringwoodite, Mg-perovskite).
Contributions to Mineralogy and Petrology, 2000
The crystal chemistry of six clinopyroxenes enclosed in protogranular spinel-peridotite mantle xe... more The crystal chemistry of six clinopyroxenes enclosed in protogranular spinel-peridotite mantle xenoliths from Lake Nji (Cameroon, W Africa) was studied by means of single-crystal X-ray diraction and electron microprobe. These spinel-peridotite xenoliths are characterised by clinopyroxene contents distinctly higher than those reported by for spinel-peridotite xenoliths of the same region (19±11% and 15±8% respectively) and by high clinopyroxene/orthopyroxene ratios: 0.7±2.7 (present study) and about 0.4 . The clinopyroxene crystal chemistry indicates that the xenoliths show the compositional features of a mantle source contaminated by small-volume melts, responsible for the high clinopyroxene content. The protogranular texture of the Cameroon xenoliths (upper portion of lithospheric mantle) testi®es that the spinel peridotite and the associated small-volume melts completely re-equilibrated at the spinel-peridotite facies.
The Canadian Mineralogist, 2007
The uncommon sulÞ de djerÞ sherite, ideally K 6 (Fe,Cu,Ni) 25 S 26 Cl, occurs in the dunite porti... more The uncommon sulÞ de djerÞ sherite, ideally K 6 (Fe,Cu,Ni) 25 S 26 Cl, occurs in the dunite portion of the Guli complex, located in Polar Siberia, Russia. Distinctive features of the Guli complex are its considerable size, ~2000 km 2 , making it the largest dunite-clinopyroxenite massif in the world, and its complicated geology. The exposed part is composed predominantly (60%) of variably serpentinized dunite. Melanocratic alkaline rocks cover about 30%, and other rock types, including melilitolite, ijolite, alkaline syenite and carbonatite, occupy less than 10% of the area. The sample with the most abundant djerÞ sherite is a coarsegrained phlogopite-magnetite-rich clinopyroxenite. DjerÞ sherite most commonly occurs in irregular patches of sulÞ de composed mainly of pyrrhotite accompanied by minor chalcopyrite and rare galena, in a matrix of Ti-bearing andradite, clinopyroxene, phlogopite, plagioclase, apatite and rare zircon, titanite and pyrophanite. It forms crystals generally less than 100 m in size and occurs as irregular single-phase grains or it Þ lls Þ ssures of the silicate matrix and inÞ ltrates phlogopite along its cleavage planes. We provide new data on the physical and crystallographic properties of djerÞ sherite. Its composition is characterized by an extensive substitution among Fe, Cu and Ni; their reciprocal substitutions are mainly controlled by the nature of the host rock. The djerÞ sherite from the Guli complex is Cu-rich and resembles that reported from alkaline rocks. This feature is consistent with the proposal that djerÞ sherite in the Guli complex crystallized as a primary mineral, during the late-stage fractionation of a highly alkaline melt portion, derived from successive fractional melting of an ascending mantle plume under metasomatic conditions. SOMMAIRE La djerÞ sherite, de formule idéale K 6 (Fe,Cu,Ni) 25 S 26 Cl, sulfure assez inhabituel, a été trouvée dans la dunite du complexe de Guli, située en Sibérie polaire, en Russie. Le complexe de Guli se distingue par sa dimension, environ 2000 km 2 , ce qui en fait le massif de dunite-clinopyroxénite le plus grand au monde, et par la complexité des relations géologiques. Les afß eurements consistent surtout (60%) de dunite variablement serpentinisée. Les roches alcalines mélanocratiques couvrent environ 30%, et les autres variétés de roches, y inclus mélilitolite, ijolite, syénite alcaline et carbonatite, occupent moins de 10% de la superÞ cie. L'échantillon contenant la plus grande proportion de djerÞ sherite est une clinopyroxénite à phlogopite-magnétite à gros grains. La djerÞ sherite se présente surtout en amas irréguliers de sulfures faits de pyrrhotite avec chalcopyrite accessoire et galène plus rare, dans une matrice d'andradite titanifère, clinopyroxène, phlogopite, plagioclase, apatite, et zircon, titanite et pyrophanite plus rares. Elle se présente en monocristaux irréguliers, généralement de moins de 100 m, ou bien elle remplit les Þ ssures dans la matrice silicatée et s'inÞ ltre dans la phlogopite le long de clivages. Nous avons effectué de nouvelles mesures des propriétés §
Neues Jahrbuch für Mineralogie - Abhandlungen, 2008
The pre-Neogene subcontinental lithosphere beneath the Carpathian-Pannonian region is poorly stud... more The pre-Neogene subcontinental lithosphere beneath the Carpathian-Pannonian region is poorly studied and the mantle beneath the Tisza Unit (S Hungary) is known only from the rare occurrence of mantle xenoliths in Late Cretaceous lamprophyre dykes in the Villány Mts. This paper presents clinopyroxene and spinel single-crystal X-ray diffraction studies from spinel lherzolite xenoliths from this locality. Clinopyroxene unit cell volumes are signifi cantly high (up to 437 Å 3 ) and show fi nal equilibrium pressures near to the plagioclase stability fi eld. Unit cell parameters of the spinel crystals range from 8.1479 to 8.1541 Å, and are directly related with their low cr#. Oxygen atomic coordinates u are equal to 0.2628 and suggest slow cooling of the samples related to the subvolcanic character of the host rock. Crystal structure and thermobarometrical data of the xenoliths, together with a detailed petrographical study, indicate recrystallization and re-equilibration of the sampled mantle section under low PT conditions.
Uploads
Papers by Francesco Princivalle