Emanuele Costa

The competition between {} cleavage and {} steep rhombohedra in gel grown calcite crystals

Abstract Calcite crystals have been obtained from supersaturated solutions diffusing both in agarose and Na-metasilicate gels. Crystal morphology in agarose is characterized mainly by spherulites grown around solid gel impurities and terminated by the cleavage {1 0 1 4} rhombohedron. Grown from Na-metasilicate gel, {1 0 1 4} and {0 1 1 2} rhombohedra compete according to the influence of pH and of the acidifying agent, HCl or CH3COOH, the latter favouring the appearance of the {0 1 1 2} form.

Fragments of the Western Alpine Chain as Historic Ornamental Stones in Turin (Italy): Enhancement of Urban Geological Heritage through Geotourism

In Piemonte, stone has always been the most widely used raw material for buildings, characterizing the architectural identity of the city of Turin. All kinds of rocks, metamorphic, igneous, and sedimentary, are represented, including gneisses, marbles, granitoids, and, less commonly, limestones. The great variety of ornamental stones is clearly due to the highly composite geological nature of the Piemonte region related to the presence of the orogenic Alpine chain and the sedimentary Tertiary Piemonte Basin. This paper provides a representative list of the most historic ornamental stones of Piemonte, which have been used over the centuries in buildings and architecture. The main stones occurring in Turin have been identified and described from a petrographic and mineralogical point of view in order to find out the corresponding geological units and quarry sites, from which they were exploited. This allows the associated cultural and scientific interest of stones to be emphasized in the architecture of a town which lies between a mountain chain and a hilly region.

Messinian halite and residual facies in the Crotone basin (Calabria, Italy)

Abstract The Neogene Crotone basin in eastern Calabria contains extensive Messinian evaporite deposits, including thick gypsarenite and halite. The halite deposit reaches a maximum thickness of c. 300 m and in some areas forms relatively small diapirs piercing late Messinian and Pliocene sediments. Halite is strongly modified by folding and recrystallization, but a few primary features are preserved. Four primary halite facies have been recognized: (a) banded halite consisting of folded white and dark bands deposited in a salt pan and/or saline mudflat; (b) white facies, massive halite containing anhydrite nodules, probably formed in a variably desiccating saline lake; (c) clear facies made up of a mosaic of large blocky halite crystals separated by mud, possibly the product of displacive halite growth in a saline mudflat; and (d) breccia facies, a product of dissolution of halite/mudstone/siltstone layers. Residual facies formed from halite dissolution are present as both weld and cap rocks. Weld rocks are thick, undeformed, and composed only of insoluble phases originally included in the salt, whereas cap rocks are thin, strongly sheared and include clasts from the cover rocks.

Metamorphic CO2 Degassing in the Active Himalayan Orogen: Exploring the Influence of Orogenic Activity on the Long-Term Global Climate Changes

A number of studies suggest that mountain ranges have strong impact on the global carbon cycle; metamorphic degassing from active collisional orogens supplies a significant fraction of the global solid-Earth derived CO2 to the atmosphere, thus playing a fundamental role even in today’s Earth carbon cycle. The Himalayan belt, a major collisional orogen still active today, is a likely candidate for the production of a large amount of metamorphic CO2 that may have caused changes in long-term climate of the past, present and near future. Large metamorphic CO2 fluxes are facilitated by rapid prograde metamorphism of big volumes of impure carbonate rocks coupled with facile escape of CO2 to the Earth’s surface. So far, the incomplete knowledge of the nature, magnitude and distribution of the CO2-producing processes hampered a reliable quantitative modeling of metamorphic CO2 fluxes from the Himalayan belt. This study, integrated in the framework of the Ev-K2-CNR SHARE (Stations at High Altitude for Research on the Environment) Project, focuses on the metamorphic decarbonation processes occurring during the Himalayan collision. We hereby present preliminary results focusing on the distribution of different types of metacarbonate rocks in the Eastern Himalaya, their petrographic description and the first reported petrological data about the nature of the CO2-producing reactions in garnet-bearing calc-silicate rocks. These results represent a contribution toward a better understanding of the influence exerted by orogenic processes on climatic changes at global scale.

Stone materials used for monumental buildings in the historical centre of Turin (NW Italy): architectonical survey and petrographic characterization of Via Roma

Abstract One of the peculiarities of Turin (NW Italy) lies on the presence of monumental arcades which mainly consist of stone material. These arcades, characterized by more than 12 km of interconnected paths, represent one of the widest city promenades of Europe and are an architectural, aesthetic and socio-economic example unique in the world. This paper, analysing the urban axis of Via Roma (Rome Street), aims to study the material used in arcade construction. The main stones occurring in Via Roma have been identified and described from a petrographic and mineralogical point of view in order to find out the corresponding geological units and original quarry sites. The minero-petrographic study is accompanied by an architectural survey that was performed applying different methods, as well as the geometric mapping and the perspective rectification of span-types, of block terminations and of other architectonical elements, in plan and in elevation, of the arcades. This allows us to emphasize the merging of cultural and scientific interest for the stone materials used in the historical architecture of a town closely interconnected to the surrounding Western Alps orogenic chain.

The Ivrea Morainic Amphitheatre as a Well Preserved Record of the Quaternary Climate Variability (PROGEO-Piemonte Project, NW Italy)

In the Piedmont plain of NW Italy the Ivrea Morainic Amphitheatre (IMA) is a remarkable evidence of the Quaternary glaciations. It consists of a wide (505 km2) complex of lateral moraines (i.e. the Serra d’Ivrea), end moraines and kame terraces, encircling a 200 km2 wide flat internal depression above which a subglacially moulded rocky hills (the Colli d’Ivrea) elevates. The glacigenic succession ranges from the end of the Early Pleistocene (dated on palaeomagnetic basis) to the end of the Late Pleistocene (14C radiometric and 10Be exposure ages) (about 900–20 ky BP). The IMA has recently been parted into ten stratigraphical units, potentially correlable to the whole sequence of the main Quaternary glaciations recorded by the marine oxygen isotope stratigraphy. Natural (glacigenic deposits and forms) and archaeological (i.e. the Roman gold mines) features make the IMA a very interesting topic for a multidisciplinary research with educational, cultural and tourist purposes. Some recent and present activities for the land promoting are presented. A candidature to the UNESCO global geopark network is considered as a suitable and ambitious goal.

Deterioration of building materials and artworks in the ‘Santa Maria della Stella’ church, Saluzzo (Italy): Causes of decay and possible remedies

An in-depth scientific survey revealed the deterioration mechanisms affecting the ‘Santa Maria della Stella’ church in Saluzzo, Italy, where various salt crystallization processes are strongly damaging the building materials and artworks. Rainwater seepage permeates the vault and interior, causing: (1) epsomite growth as interstitial columnar crystals (resulting in pictorial coating detachment) or superficial, powdery efflorescence; (2) formation of nesquehonite/hydromagnesite crusts on wall paintings; and (3) nitratine growth causing pigment staining and detachment. These processes involve selective Mg2+ mobilization from magnesian-lime mortars and bacterial-induced formation of nitrates from guano, with consequent precipitation of degrading salts. The study confirms how characterization of all deterioration agents is fundamental to planning a viable cultural heritage conservation and restoration programme.

Preliminary Chemical and Isotopic Characterization of High-Altitude Spring Waters from Eastern Nepal Himalaya

Metamorphic degassing from active collisional orogens supplies a significant fraction of CO2 to the atmosphere, thus playing a fundamental role even in today’s Earth carbon cycle. Appealing clues for a contemporary metamorphic CO2 production in active orogens are represented by the widespread occurrence, along the whole Himalayan belt, of CO2 rich hot-springs mainly localized along major tectonic discontinuities. In contrast to these well-studied hot-springs, almost no chemical and isotopic data are actually available for cold-springs, especially for those located at high-altitude and in remote areas of the Himalayas. In the framework of the Ev-K2-CNR SHARE (Stations at High Altitude for Research on the Environment) Project, we have started a preliminary chemical and isotopic study on high-altitude cold-springs located at different structural levels in the eastern Nepal Himalayas. Chemical and isotopic data obtained from the high-altitude cold-springs are compared with those obtained by previous authors from hot-springs located along the MCT. The isotopic signature of stable isotopes of hydrogen and oxygen could help to identify the waters sources in the investigated Himalayan sectors, to individuate mixing phenomena between waters of different provenience and possible connection with different circulation nets. These first measurements on high-altitude springs from remote areas of eastern Nepal represent a first step towards a better definition of a reliable scenario of water resources availability and will contribute to the understanding of the water cycle in the studied area.

“Mohsite” of Colomba: Identification as Dessauite-(Y)

During a reorganization of the mineralogical collection of Turin University, old samples of the so-called mohsite of Colomba were found. “Mohsite” was discredited in 1979 by Kelly et al., as a result of some analyses performed on the equivalent material coming from the French region of Hautes-Alpes, but the original samples found in similar geological setting in Italy were lost and never analysed with modern equipment. After more than a century, the rediscovered samples of Professor Colomba were analysed by means of SEM-EDS analysis, microRaman spectroscopy, and X-ray diffraction. The results have demonstrated that the historical samples studied by Colomba are Pb-free dessauite-(Y), and pointed to an idealized crystal chemical formula (Sr0.70Na0.25Ca0.09)Σ=1.04 (Y0.62U0.18Yb0.09Sc0.08)Σ=0.97 (Ti12.66)Σ=17.70O38 and unit-cell parameters a = 10.376(3) A, c = 20.903(6) A, and V = 1949(1) A3.

Investigation about ancient mortars and plasters in the Mondovì cathedral (Cuneo, Italy)

St. Donato Cathedral of Mondovi (Cuneo Province, North-West Italy) is the last project of the famous architect Francesco Gallo (1672-1750). The construction started in 1744, but it has been consecrated only in 1763. The building is an impressive brick-made church with a main nave and two lateral aisles, which remarkable length is 56 meters and it is 24 meters wide. Its style is mainly baroque with some neoclassical additions. After the edification, the decoration of the interior walls was very simple; probably it was a white finish of smooth plaster consisting of lime and magnesian lime mortar. There are some evidences of a basic decoration: a uniform bluish or grayish tinge. Around 1850 a plan for a new decorative apparatus was made and some of the most important painters of that period were committed to paint sacred subjects on the vault and apse, and to provide the decorations of the walls. In early 2012 started some important restoration works in the Cathedral. One of the main purpose of the Restoration Team is to get scientific and historical information about the work of ancient painters and decorators. The scientific investigation on mortar layers was conducted on various samples, several of them were resin included polished sections, using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) supported by Energy Dispersive Microprobe spectroscopy (EDS). The analyses carried out on the samples clearly showed the historical stratifications of different layers. The first stratification is made of mortars and plasters dating around the middle of 18th century, and shows different compositions and very neat layers. While the last stratification is a more recent mortar plaster, which is coarse-grained, used as a background for the new decorations done in the middle of 19th century.