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Ancient pozzolanic mortars show the high technological quality achieved by Roman construction workers, due to their ‘excellent state’ of preservation in every environment. These workers well knew that thanks to the combination of lime with specific volcanic products (pozzolana), mortar and concrete become hydraulic, allowing underwater hardening and increasing mechanical strength. The use of pozzolana in a mortar provides the underwater curing (hydraulic limes) of whatever construction with higher speed compared to carbonation processes of slaked lime. Whenever pozzolana is not available, it is substituted by ceramic fragments, which possess similar hydraulic properties. This research focuses, for the first time, on the detailed characterization of mortars coming from the Thermal Complex of Baia, which represents one of the most important archaeological sites in the Campania region. Thanks to several thermal springs, the ancient city of Baiae (Campi Flegrei) was the holiday resort of the Roman aristocracy. The former Soprintendenza Archeologia della Campania, allowed us to perform non-invasive, but representative, sampling of mortars that were characterised by multianalytical methodologies (POM, XRPD, SEM-EDS, TGA, and MIP) providing useful information on possible future activities of restoration. Results confirmed the expertise of Roman workers, who skilfully combined volcanic tuff aggregate, hydrated lime, and ceramic fragments. In particular, the typical zeolitic mineral association of phillipsite > chabazite > analcime found in the tuff aggregate pointed out their provenance from the Neapolitan Yellow Tuff related to the volcanic activity of Campi Flegrei of ca. 15 ka BP. The most relevant characteristic detected in all studied samples is the mortar hydraulicity testified by evidences such as reaction rims between pozzolana and binder, Hydraulicity Index (HI), and thermal analyses investigation. Also, composition of secondary mineralogical phases in the cementiceous matrix is particularly relevant. Distinctive is the contemporary presence of C-A-S-H gel, calcite and gypsum. C-A-S-H gel is derived from lime/ceramic fragments reaction; calcite is likely related to the partial reaction of underburned lime; and gypsum could be ascribable to the sulphation process of calcite. These secondary minerogenetic products fill pore space and enhance bonding in pumice fragments, thus contributing to long-term durability of mortars.

Quantitative mineralogical analysis of clay-bearing rocks is often a non-trivial problem because clay minerals are characterized by complex structures and are often affected by structural disorder, layer-stacking disorder, and interstratification. In the present study, internal-standard Rietveld X-ray powder diffraction (XRPD) analyses were combined with X-ray fluorescence (XRF) chemical analyses for the mineralogical characterization and quantitative analysis of heterogeneous clay-rich sedimentary rocks that are involved in a slow-moving landslide in the Termini-Nerano area, Sorrento Peninsula (Italy), in order to investigate the relationship between the mineralogy of these rocks and landslides. Slow-moving landslides are usually considered to be associated with the more weathered and surficial parts of structurally complex slopes, and mineralogical analysis can help to clarify the degree of weathering of siliciclastic rocks. XRPD quantitative analyses were conducted by combining the Rietveld and internal standard methods in order to calculate the amounts of poorly ordered phyllosilicate clays (considered amorphous phases in Rietveld refinements) by difference from 100%. The vbAffina program was used to refine the amounts of mineral phases determined with XRPD using the element compositions determined by XRF analysis. XRPD analyses indicated that the samples mainly contain several different clay minerals, quartz, mica, and feldspars. Analysis of the clay fraction identified kaolinite, chlorite, and interstratified illite-smectite (I-S) and chlorite-smectite (C-S). The mineralogy of the materials involved in the landslide in comparison with the mineralogy of the "undisturbed" rocks showed that the landslide is located in the weathered realm that overlies an arkosic bedrock. The interstratified I-S and C-S occurred at landslide activity locations and confirmed that areas more susceptible to sliding contained the most weathered parts of the rocks and perhaps represent areas of past and currently active fluid flow.

The present research accounted for an accurate selection of representative samples from zeolitized deposits of different world geographical areas commonly mined and marketed by American and European mining companies. These geomaterials displayed high contents of clinoptilolite, phillipsite, and chabazite and were deeply characterized from mineralogical, chemical, and technological points of view. A preliminary quality control of the selected materials allowed us to determine the presence of undesired minerals and/or elements. A thermodynamic investigation of the surface exchange reactions between the selected zeolite-rich rocks and the surfactant agents (HDTMA-Br/Cl, hexadecyltrimethylammonium bromide/chloride, BC-Cl, benzalkonium-chloride, CP-Cl, cetylpiridinum-chloride) enabled us to verify the extent and the compactness of the formed micelle and to foresee their future behavior through interaction with molecules of anti-inflammatory drugs (drug delivery). The encouraging results pave the way towards good perspectives on the possible use of zeolite-rich rocks in the pharmaceutical sector through a preliminary basic protocol for the characterization and monitoring of the batches to be employed.

The Neapolitan Yellow Tuff (hereafter NYT) is definitely the building material most used in the historical architecture of Naples (Southern Italy) since Greek times. The high heterogeneity of NYT, resulting from the concomitant occurrence of lithic fragments, pumices, crystals and glass cemented by crystalline or amorphous phases, the latter highly sensitive to acid environments, define a strong attitude to weathering. This research confirmed the inhomogeneous features of this volcanic formation, within the same deposit and sometimes within the same outcrop. Based on these premises, the investigation was carried out on four most representative lithofacies, according to their different textural and petrophysical features. Actually, mechanical features are governed by two concurring factors: a) the mineralogical composition; b) the texture of the rock. In the first case, the predominance of anhydrous phases (analcime + feldspar) over zeolites improves its mechanical strength. By contrast, if the mineralogical composition is constant (similar total wt.% zeolite content), the petrophysical parameters are strictly related to the texture of the rock.

This research provides a characterization of ancient Roman mortars from “Villa del Capo di Sorrento” (commonly known as “Villa di Pollio Felice” or “Bagni della Regina Giovanna”). A deepened analysis of cementitious binding matrix and aggregates was conducted with the aims of determining possible sources of raw materials and the mix recipe, and to evaluate the minerogenetic secondary processes. Twenty samples taken from the Villa were investigated by means of a multi-analytical approach, including polarized optical microscopy on thin sections, X-ray powder diffraction, scanning electron microscopy analysis, energy dispersed spectrometry, simultaneous thermal analyses, and mercury intrusion porosimetry. Bedding mortars were made with slaked lime mixed with volcanic materials, whereas coating mortars were made adding to previous recipe as ceramic fragments. All samples were classified as hydraulic mortars. Cementitious binding matrix was characterized by gel-like C-A-S-H, calcite, hydrocalumite, and gypsum, deriving from lime/pozzolanic material. Geomaterials used for mortar production had a local origin. Pozzolanic materials, such as volcanic fragments, scoriae, pumice, and crystal fragments derived from both pyroclastic rocks of the Campi Flegrei district and from rocks of the Somma-Vesuvio complex, porosity test suggest that the products related to minerogenetic secondary processes, make mortars more resistant.

Two zeolite-rich rock samples extracted from Campanian Ignimbrite tuff quarries, southern Italy, usually used as binding and anticaking agents in animal feeding, were characterized and tested in terms of their resistance in stomach, small and large intestine of pig, using a three step in vitro digestibility trial. The mineralogical composition and major and trace-elements analysis were performed after each digestion step using XRPD and ICP-OES techniques. The main zeolite phases identified are phillipsite and chabazite. Results showed that in vitro physical-chemical conditions (pH 2–3 and T 39 °C) the release of Pb and other elements from the zeolite structure is extremely low and due to the limited breakdown of the zeolite framework and glass/amorphous matter hydrolysis, by the gastric liquids. This aspect also suggests that zeolites, after the total permanence in the animal body digestive tract, can further perform their important function of cation exchanger, with also relevant relapses on the growth and health of the animal species, as well as on the environment. Moreover, the contact of zeolite material with liquids of small and large intestine leads to negligible release of undesirable elements, which are far less than those envisaged by the European Regulations.

Fourteen samples of tourmaline from the Real Museo Mineralogico of Federico II University (Naples) have been characterized through multi-methodological investigations (EMPA-WDS, SEM-EDS, LA-ICP-MS, and FT-IR spectroscopy). The samples show different size, morphology and color, and are often associated with other minerals. Data on major and minor elements allowed to identify and classify tourmalines as follows: elbaites, tsilaisite, schorl, dravites, uvites and rossmanite. Non-invasive, non-destructive FT-IR and in-situ analyses were carried out on the same samples to validate this chemically-based identification and classification. The results of this research show that a complete characterization of this mineral species, usually time-consuming and expensive, can be successfully achieved through non-destructive FT-IR technique, thus representing a reliable tool for a fast classification extremely useful to plan further analytical strategies, as well as to support gemological appraisals.

Author(s): Jackson, MD; Mulcahy, SR; Chen, H; Li, Y; Li, Q; Cappelletti, P; Wenk, HR | Abstract: Pozzolanic reaction of volcanic ash with hydrated lime is thought to dominate the cementing fabric and durability of 2000-year-old Roman harbor concrete. Pliny the Elder, however, in first century CE emphasized rock-like cementitious processes involving volcanic ash (pulvis) "that as soon as it comes into contact with the waves of the sea and is submerged becomes a single stone mass (fierem unum lapidem), impregnable to the waves and every day stronger" (Naturalis Historia 35.166). Pozzolanic crystallization of Al-tobermorite, a rare, hydrothermal, calcium-silicate-hydrate mineral with cation exchange capabilities, has been previously recognized in relict lime clasts of the concrete. Synchrotron-based X-ray microdiffraction maps of cementitious microstructures in Baianus Sinus and Portus Neronis submarine breakwaters and a Portus Cosanus subaerial pier now reveal that Al-tobermorite also occurs in the leached perimeters of feldspar fragments, zeolitized pumice vesicles, and in situ phillipsite fabrics in relict pores. Production of alkaline pore fluids through dissolution-precipitation, cation-exchange and/or carbonation reactions with Campi Flegrei ash components, similar to processes in altered trachytic and basaltic tuffs, created multiple pathways to post-pozzolanic phillipsite and Al-tobermorite crystallization at ambient seawater and surface temperatures. Long-term chemical resilience of the concrete evidently relied on water-rock interactions, as Pliny the Elder inferred. Raman spectroscopic analyses of Baianus Sinus Al-tobermorite in diverse microstructural environments indicate a cross-linked structure with Al3+ substitution for Si4+ in Q3 tetrahedral sites, and suggest coupled [Al3++Na+] substitution and potential for cation exchange. The mineral fabrics provide a geoarchaeological prototype for developing cementitious processes through low-temperature rock-fluid interactions, subsequent to an initial phase of reaction with lime that defines the activity of natural pozzolans. These processes have relevance to carbonation reactions in storage reservoirs for CO2 in pyroclastic rocks, production of alkali-activated mineral cements in maritime concretes, and regenerative cementitious resilience in waste encapsulations using natural volcanic pozzolans.

The pozzolanic action played by five natural zeolite-rich materials (three clinoptilolite- and one each mordenite- and analcime-bearing rocks) coming from Turkey, has been examined, evaluating also the influence of various chemical–physical parameters, such as grain size of the zeolitic materials and nature of the cation present as extra-framework component of the structure. Pozzolan activity has been estimated by the official test of the European Standards and by thermogravimetry, finding a good accordance between the two procedures. Clinoptilolite-rich rocks gave the best results, but performance turned out to depend on the specific surface area and pre-enrichment in a potassium form. Experimental data analysis demonstrated that the pozzolanic reaction is kinetically controlled by the diffusion of reactants through a layer of dense reaction products. Experimental blended cements with the five zeolite-rich rocks were also prepared and the compressive strengths measured as a function of the curing time. The effectiveness of the pozzolanic action was monitored by XRD and FTIR analyses. An accurate microstructural study of the hardened pastes was also carried out and point analysis performed, pointing out that the zeolite-lime interaction is characterized by two stages: initially zeolite subtracts calcium from the environment by cation exchange, then it acts as a true pozzolan as soon as its structure breaks down.

This paper aims at testing the use of mixtures constituted by natural zeolitized products and SiC-bearing industrial wastes (sludge deriving from polishing of porcelain stoneware tiles, hereafter DPM) for the production of lightweight expanded aggregates as constituents of structural and/or thermo-insulating lightweight concretes. Two commercial products have been used as zeolite natural source: Cab70 (Yellow facies of Campanian Ignimbrite) and IZclino (Turkish clinoptilolite-rich epiclastite). Different amounts of a calcareous material (Pozzano limestones — hereafter CP) from the Sorrento peninsula (Naples — Italy) were also added to a Cab70–DPM mixture. All raw materials were characterized by means of mineralogical (XRPD) and chemical (XRF) analyses. All the products and mixtures were tested from a technological point of view by means of fusibility and firing tests in order to evaluate the expanding properties. It was evidenced that the expansion of the mixture was deeply depending on the occurrence of SiC in the industrial waste. The addition of CP (10 wt.%) to the mixtures accounts for an even increased expansion, though this is accompanied by a worsening of the mechanical features of the material. These results along with literature data allowed to select 3 mixtures (70% Cab70–30% DPM, 70% IZclino–30% DPM, 60% Cab70–30% DPM–10% CP) and each of them was used for the preparation of 5 l of lightweight aggregates afterward employed for the manufacture of lightweight concretes. It was remarked that natural zeolitized materials mixed with DPM (30 wt.%) can provide lightweight aggregates with densities ranging between 0.8 and 1.0 g/cm 3 suitable for the preparation of structural lightweight concretes. The addition to the mixture of CP (10 wt.%) produces less dense aggregates (0.6–0.7 g/cm 3 ) potentially useful for the manufacture of thermo insulating lightweight concretes.

Low-cost, naturally-occurring mixtures of feldspar and zeolite occurring in epiclastic rocks are promising substitutes for conventional quartz-feldspathic fluxes in ceramic bodies, since their fusibility and low hardness are expected to improve both grinding and sintering. Three epiclastic outcrops, with a different zeolite-to-feldspar ratio, were characterized (XRPD, fusibility) and tested in porcelain stoneware bodies; their behaviour during processing was appraised and compared with that of a reference. The addition of an epiclastic rock (20 wt.%), replacing rhyolite and aplite fluxes, brought about some significant advantages, mainly represented by better grindability, lower firing temperature with improved mechanical strength and lower porosity. Disadvantages concern increased slip viscosity, worse powder compressibility, resulting in larger firing shrinkage, and a darker colour of the tiles due to relatively high amounts of iron oxide.

Aim of this research is an evaluation of the zeolitized facies of Campanian Ignimbrite as raw material for the production of lightweight expanded aggregates (LEA). A commercial product (Cab70) was used as reference for this rock. Tests were carried out on “pure” samples or mixed with an industrial waste mud (DPM — Dried Polishing Mud) deriving from a porcelain stoneware tile polishing process. This mud contains SiC, a phase known to act as bloating enhancer. Raw materials were subjected to mineralogical (XRPD–RIR method) and chemical (XRF) analyses. Bloating upon heating was measured (Leitz heating microscope) on Cab70, DPM and on three mixtures having the following Cab70/DPM ratios: 85/15 (Mix1); 70/30 (Mix2); 50/50 (Mix3). LEA production was assessed both in static (muffle kiln) and in dynamic (rotating kiln) conditions by firing pellets, 3–8 mm in size, between 1220–1380 °C. The unit weight of the single particle was determined on fired and unfired products. All materials evidenced a decreasing density with temperature whereas the same parameter decreases with DPM increasing content. Cab70 LEAs never dropped below 0.90 g/cm3, even at the highest temperature, whereas DPM LEAs range between 0.86 g/cm3 (at 1260 °C) and 0.46 g/cm3 (at 1380 °C). A direct but not linear relationship between DPM content and density was evidenced. Among the three mixtures, Mix2 showed the lowest DPM content able to produce the strongest density reduction. To get LEAs with the same density the rotating kiln required temperatures generally 60–80 °C higher than those of the muffle kiln. This difference should be related to the different thermal insulation of the two systems during firing. Two sets of LEAs were massively produced in dynamic conditions from Cab70 (at 1380 °C) and Mix2 (at 1300 °C). These latter showed better technical performances in terms of unit weight of the single particle (0.81 vs. 0.98 g/cm3), bulk unit weight (460 vs. 565 kg/m3), water absorption coefficients (1.4 vs. 5.5% after 24 h) and compressive strength of the particles (2.9 vs. 0.6 MPa). Differences in pore shape, dimension, abundance and spatial distribution were observed by SEM between the two sets. The technical features of these LEAs were comparable to some expanded clays, with similar grain size, commercialised in Italy. These results are worth interesting as they reveal new perspectives of application both for a rock characterized by a low exploitation cost and widely available in central-southern Italy, as well as for an industrial waste produced in high amount but not recycled at all.

This paper reports novel data concerning the volcanic formation of the Piperno, a stone that has been used for a long time in the monumental architecture of Naples and the Campanian region (Southern Italy). A careful field survey of the outcrops or underground sites so far accessible allowed us to draw a lithostratigraphic reconstruction of the formation and enabled the recognition of the three main layers exploited in past centuries and which provided dimension stones for architectural and structural purposes. Petrophysical and mineralogical characterization also enabled us to discriminate the same layers previously identified. Different scoriae/matrix ratio, scoriae dimension and welding degree are the most peculiar features of these horizons. The combination of these three parameters, even though they did not affect the use of Piperno as dimension stone, somehow determined its variable susceptibility to the weathering agents. However, a linear relationship between the exposure time and the decay of the stone itself, at a parity of weathering intensity, was not observed. This assumption was proved by verifying that the specific layers of the volcanic sequence controlled the weathering degree of Piperno from monuments disregarding their age of emplacement.

The thermal behavior of two clinoptilolites from an epiclastic and a pyroclastic deposit of central-northern Sardinia and of their exchanged forms (Li, Na, K, Cs, Mg, Ca, Sr and ammonium) were investigated by differential thermal analysis and thermogravimetry up to 1000°C. Their thermal stability was studied by evaluating the residual crystallinity (expressed as rehydration capacity) after 2 h thermal treatments at 450, 600 and 900°C. The water loss at 1000°C was linearly related to the radius (r) and the charge (z) of the exchangeable cations by the equations r2/z or r3/z, which are proportional to the inverse of the charge density over the surface or to the charge density over the volume of the cations. The cation composition plays a crucial role in determining the thermal behavior of clinoptilolite. The presence of cations such as Cs or K, which have low surface or volume charge densities, was found to increase the thermal resistance. In particular, the crystallinity of Cs- and K-exchanged forms of both clinoptilolites was not affected by thermal treatment at 450°C and was only slightly reduced by thermal treatment at 600°C. Predicting the thermal behavior of natural and cation-exchanged forms of these clinoptilolites can provide useful information for possible applications in catalysis, in the case of high thermal stability, or for thermal transformation into ceramics or lightweight aggregates.

The zeolitic minerals have been observed in volcanic sequences of recent geologic age (Pliocene–Miocene) that have been located around the Laguna de Cuitzeo and near Morelia (Capital of the State of Michoacan, Mexico). The zeolites of the Cuitzeo area were studied by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), X-ray fluorescence (XRF), FTIR and Raman spectroscopy in combination with thermoanalytical methods (thermogravimetric analysis — TG/DTG — and differential thermal analysis — DTA). The main mineral constituent is an intermediate type of the isomorfous series heulandite–clinoptilolite end members. Trace of feldspars, biotite, and smectite (and an amorphous fraction) were also detected. Chemical composition (Ca 1.44–2.00 K 1.44–0.74 Na 0.05–0.53 Mg 0.67–0.92 Fe 0.02–0.10 )[Si 29.04–29.85 Al 6.31–7.04 O 72 ] 13.5 H 2 O and some chemical features (Γ = 0.96–1.08), (Si/Al ratio 4.47; Al + Fe 3 + of 6.36 to 7.13) with 2.38 (Mg + Ca) > 1.43 (Na + K) correspond to the intermediate member of the clinoptilolite–heulandite isomorphous series. The dehydration rate of the Cuitzeo zeolites, especially in the range from 150 to 400 °C, as well as spectroscopic features (FTIR and Raman), external cation exchange capacity (135 meq kg − 1 ) and porosimetric data are also characteristic for this intermediate clinoptilolite–heulandite member. The value of the BET specific surface area (20.3 m 2 /g) is about 1.5 times higher than that relative to clinoptilolite-rich tuff powders of different geographic origin and previously characterized. Cuitzeo zeolite deposit is of a great economic interest, considering that it is the unique and richest among the zeolite formations in Southwestern Mexico with zeolite content higher than 70 wt.%. This value is relatively high: most of the exploited zeolitic tuffs from the Oaxaca State (the most studied and well known deposits of natural zeolites in the south of Mexico) have been estimated to contain less than 60 wt.% zeolite minerals. Based on the above properties the zeolite from Cuitzeo area could be a very effective tool for technological application (such as agricultural use, decontamination of water and soils, cement industry, etc.), particularly due so far of the complete absence of zeolitic deposits in the central region of Mexico.

This paper investigates the thermal transformation of powders of volcanic tuffs that are used as building stones and aims at thermally transforming them into ceramics. The following positive indications concerning this thermal transformation were found: (1) the structural evolution which brings products similar to traditional ceramics, (2) the good ability to give rise to dense and compact final products, and (3) the good mechanical properties and the lovely appearance of the final products. Nevertheless, the high values of linear shrinkages recorded in this work seem to strongly hinder the thermal transformation of this powder-like waste into ceramics. However, mixing this by-product with other powder-like waste exhibiting higher-dimensional stability, such as those deriving from sawing of granites, appears proper.

A detailed mineralogical and petro-physical characterization was carried out on Campanian Ignimbrite (CI) formation, a volcaniclastic rock widespread over the Campania region. This stone represented and still is an important building material since historical times. Given the huge extension of this formation (about 30 000 km 2 ) the attention was mainly focused on the historical exploitation areas that provided building materials for the medieval village of Casertavecchia. Building stones (different facies of CI) used facciavista in some relevant monuments of this village were also characterized to carry out a comparison with the in situ corresponding rock. At the same time a complete survey of all the lithotypes used for the facades of the village as well as their state of conservation and weathering phenomena was also performed. As expected, CI in its different facies resulted the most common building stone, also affected by severe weathering such as lacks, alveolization and biological patinae, decay forms likely related to the high textural heterogeneity of the rock. Mineralogical and petro-physical characterization allowed to distinguish, within the investigated outcrop area, three different facies: dark, light and earthy grey tuff (DGT, LGT and EGT, respectively). Differences in mineralogical data mainly consist in the presence of clay minerals in the EGT facies only. K-feldspar always occurs in very high amounts (80–90%). As far as geomechanical parameters are concerned, the most pronounced differences are recorded in water absorption capacity, ultrasonic velocities and UCS values. These tests evidenced a substantial homogeneity of DGT and LGT facies and an overall worse behavior of EGT. Tests performed on CI samples from both monuments and outcrops gave similar results. This evidence strengthened the former hypothesis of a location of CI historical quarrying sites close to Casertavecchia. The only exception is the tuff used for the Mastio of the castle, whose chemical features are definitely referable to a different volcaniclastic formation. © 2004 Elsevier SAS. All rights reserved.

The aim of this research is to assess the possible use of Italian zeolitic rocks for the production of lightweight aggregates. In particular, both the expansion at high temperature and the technological features of fired products were investigated. Fifteen zeolite-bearing volcanoclastites from Northern Sardinia and three zeolitized tuffs from Campania and Tuscany (Sorano and Campanian ignimbrites and Neapolitan Yellow Tuff) were taken into account. The firing expansion turned out to be mainly dependent on the chemical composition (especially SiO 2 and fluxing oxides such as Fe 2 O 3 , Na 2 O, K 2 O, MgO and CaO) and the water content (largely related to the zeolite amount) of the raw materials. Other relevant parameters were the temperature of maximum expansion (ranging between 1350 and 1500 °C, without additives) and soaking time (between 2 and 5 min). Some products are highly impervious to water (water absorption below 1%) and exhibit a considerable firing expansion (>100% in volume), a low bulk density (0.5–0.7 g·cm −3 ) and fair technical properties (loose weight and strength of particles). These encouraging results make some of the investigated tuffs interesting raw materials for the production of lightweight aggregates.

An attempt to correlate differnt facies of an important volcaniclastic formation of southern Italy, the Campanian Ignimbrite, with their zeolite content and physico-mechanical properties was carried out. The following parameters were measured: total zeolite content, solid unit weight (γ s ), porosity, and uniaxial compressive strength. Samples were formerly grouped on the basis of the displayed colour in four categories each of them characterized by a different zeolite grade. An increase of zeolite content determines a decrease of porosity and a good positive correlation with UCS values. The relationship existing between zeolite grade and UCS becomes less pronounced or even lost, when zeolite content reaches about 50% wt. Here, UCS values scatter in a quite wide range (3–6 MPa). It is hypothesized that the lithification of zeolite-bearing rocks is the result of two combined effects playing a different role during the zeolitization process: the transformation of the amorphous fraction in zeolite and the rock texture. In the first stage of the zeolitization process the role played by the rock texture (clasts/matrix ratio, pumice concentration, fractures, etc.) is totally masked by the overwhelming behaviour of zeolite itself up to that threshold value, above which the influence of these two leading parameters is inverted.

Publisher Summary This chapter discusses the natural zeolites mineralization in the oligocene–miocene volcano-sedimentary succession of Central Sardinia. The investigations performed on the Cenozoic volcano-sedimentary sequence of Central Sardinia recognize widespread secondary mineralization processes, differently affecting the volcanic and sedimentary units cropping out in the region. Mineralogical studies confirm zeolite mineral association consisting of clinoptilolite and mordenite, locally attaining economic concentrations. Chemical composition of mordenite and clinoptilolite is strongly correlated with the rhyodacitic glassy precursor. Secondary mineralization process, which affects the volcaniclastic and epiclastic deposits, enables to identify the most interesting areas, as far as zeolite grade is concerned.

Publisher Summary In Campania region (Southern Italy), the large availability of volcanic products determined the utilization of these products for structural purposes. Neapolitan Yellow Tuff (NYT), Campanian Ignimbrite (CI), and Piperno (PI) were the most widely used volcanic products in historical architecture of Campania region.. This chapter describes the mineralogical and petrographical features of these materials and the research conducted to study the decay phenomena by means of laboratory simulations, which reproduce the aging processes of the stone. Mineralogical characterization was carried out by scanning electron microscopy (SEM) observations and by X-ray powder diffraction analysis (XRPD). Open porosity was calculated by He-pycnometer. Water absorption was measured by immersion test. Ageing tests, wet-dry and salt crystallization tests, were performed to study the decay phenomena. From the mineralogical analysis, a substantial difference was found out between the NYT on one side, and CI and PI on the other. The matrix of the former is mainly constituted by zeolites, amorphous phases, and volcanic glass; and the latter (CI and PI) have a matrix constituted by feldspars and minor amount of glass. The chapter provides table to illustrate variation of the physico-mechanical properties (porosity, water absorption, and uniaxial compressive strength) after aging tests. The overall results obtained show poorer durability of Neapolitan Yellow Tuff, when compared to other stones.

Experiments on zeolitization were conducted on four synthetic monocationic glasses (Na, K, Ca, or Mg-rich glass) with Si/Al molar ratios of 2.67, similar in acidity to many volcanic glasses of partially zeolitized Italian tuffs. The products of the hydrothermal treatment at 100, 150, and 200°C of single glasses or glass mixtures with deionized H2O or monosaline solutions (NaCl, KCl, CaCl2) were characterized by X-ray diffraction, thermal, microscopic and chemical analyses. Chemical analyses of mother liquors were also performed. Mineral assemblages, containing chabazite, phillipsite, analcime, and K-feldspar, very similar to those found in altered, volcaniclastic alkali-trachytic or trachytic glass deposits were produced. Potassium was essential to chabazite and phillipsite crystallization, although phillipsite was obtained also in Ca-Na mixed systems. Sodium was necessary for analcime formation. Calcium plays only a secondary role in zeolitization, and magnesium does not favor zeolite crystallization but promotes the formation of smectite. Glass composition determines the mineral assemblages obtained and hence in those commonly found in nature.

Volcaniclastic products of Northern Sardinia (Italy) turned out to be affected by diffuse zeolitisation processes. About 130 samples, representative of the identified formations (pyroclastic flows and epiclastic deposits), were collected in order to evaluate the distribution of zeolitic phases. Clinoptilolite was the most widespread zeolite, whereas mordenite and chabazite rarely occured. A quantitative evaluation performed by the Reference Intensity Ratio (RIR) and Rietveld methods indicated that about 30% and 44% of samples from pyroclastic flows and epiclastic deposits, respectively, have a zeolite content higher than 50%.

Two clinoptilolites from genetically different volcanoclastic formations have been studied. Both deposits are located in the Logudoro region (North-Western Sardinia, Italy) within epiclastic and pyroclastic formations related to calcalkaline volcanic activity. Chemical characterization performed by electron microprobe analysis on both samples showed a quite similar composition ([Si/(Si+Al)] = 0.81/0.82), with the exception of some extra-framework cations. In particular the epiclastic clinoptilolites turned out to be much higher in Mg content (0.72 vs. 0.26 a.f.u.) and considerably lower in K (1.10 vs. 2.37 a.f.u.) than the pyroclastic clinoptilolites. Previous investigations evidenced a different behaviour of the two clinoptilolite samples towards cation exchange processes and a substantial difference between the theoretical and experimental CEC. In this frame, Rietveld refinements based on synchrotron data allowed to define a different cationic population within the four exchangeable cation sites.