Geological features technological characterization and weathering Cusano 1

ABSTRACT

Bryozoan and Lithothamnion limestones (BLL) from central-southern Italy, commercially known as Perlato Royal Coreno, wereused for a long time in the monumental architecture of the Campa-nia and Lazio regions.

In this paper, new mineralogical-petrographical and engineering-geological data about BLL are reported and the relations between thelithofacial and technical features of this stone are investigated.

A field survey of the main limestone outcrops allowed a lithostrati-graphic reconstruction of this formation to be drawn and the eightmain lithotypes presently used as dimension stones to be recognized.

Mineralogical and petrographical characterization was performedby means of X-ray powder diffraction and optical microscopy observa-tion of thin sections (under transmitted, UV-reflected light and coldcathodoluminescence). Petrophysical characterization enabled to com-pare some engineering-geological properties and to evaluate the influ-ences of rock fabric, chemical composition, fractures and stylolithes onthe technical features of the stone. Ageing tests were also performed.

Finally the main weathering phenomena affecting the stonewere recognised through a detailed study on the facades of the belltower of the Santa Chiara monastery in Naples.

KEY WORDS: Bryozoan and Lithothamnion Limestones,lithofacies, engineering-geological properties, central-southern Italy, weathering.

INTRODUCTION

Limestones are among the most common sedimen-tary rocks in the world and are widely used in construc-tion as building stones (ALMESBERGER et alii, 2000; CAL-CATERRA et alii, 2003; DE VITO et alii, 2004; TÖRÖK et alii,2004; CARTA et alii, 2005; ALLOCCA et alii, 2010) and/or asraw material for manufacturing lime and cement.Depending on depositional environment and diagenesis,limestones show an extremely wide range of rock fabricsfrom very dense varieties to highly porous rocks (JERRYLUCIA et alii, 2001; PRIKRYL & PRIKRYLOVÁ, 2004; TÖRÖKet alii, 2004; EHRENBERG et alii, 2006; TÖRÖK, 2006). The

physico-mechanical behaviour of these rocks can be fur-ther affected by secondary phenomena like weldingand/or weathering (GIBSON et alii, 1997; AIRES-BARROS &DIONISIO, 2002). Pore space in particular affects physicalproperties, such as mechanical behaviour and durability.

Low porosity limestones show a surprisingly widerange of geomechanical properties (ALLOCCA et alii, 2010)seemingly controlled by the microfabric and especially bythe characters of pore space and by the lithofacial fea-tures. In fact, previous studies demonstrated that theoriginal depositional fabric and the cementation processduring diagenesis can be responsible for variance in phys-ical and technological properties of these types of rocks(LATHRAM & THIEL, 1946; MELIM et alii, 2002; TÖRÖK, 2006).

The Miocene Bryozoan and Lithothamnion lime-stones (BLL), commercially known as Perlato RoyalCoreno, crop out widely in central and southern Italy(Lazio, Campania and Abruzzo regions). These rocks havebeen extensively employed from Roman times (as demon-strated by several findings in the archaeological sites ofMinturno, Cassino and Pompei, fig. 1a, b), through theMedieval period (e.g., the bell tower of the Santa Chiaramonastery in Naples, fig. 1c) to modern times (e.g., the19th century Bourbon Bridge on the Garigliano river inMinturno, fig. 1d). They are appreciated as valuablebuilding material today as well (e.g., the MontecassinoAbbey, rebuilt in the 1950s after being destroyed duringWorld War II, fig. 1e).

Although numerous studies focused on the sedimen-tological and stratigraphical features of the BLL (SELLI,1957; D’ARGENIO, 1961, 1967; ZALAFFI, 1963; IPPOLITO etalii, 1973; BARBERA et alii, 1978, 1980; CORDA & BRAN-DANO, 2003; CIVITELLI & BRANDANO, 2005), little isknown about their mineralogical-petrographical and geo-mechanical parameters (CONSORZIO PER LA VALORIZ-ZAZIONE DEL PERLATO CORENO, 2002).

The present study aims to fill this gap by investigatingthe relations between the BLL lithofacies characters andtheir physical and mechanical properties.

GEOLOGICAL SETTING

The BLL crop out in several areas of the central andsouthern Apennines (fig. 2), including Matese Mts., Mt.Camposauro, Trebulani Mts., Mt. Massico, Aurunci Mts.and the hills south of Cassino, such as Mt. Trocchio andMt. Porchio (ACCORDI et alii, 1988; BONARDI et alii, 1988).

(*) Dipartimento di Scienze della Terra, Università degli Studidi Napoli Federico II, Via Mezzocannone, 8 - 80134, Napoli, Italia;e-mail address: [email protected]; mobile: +393293711407;fax: +390812538318.

(**) Dipartimento di Ingegneria Idraulica, Geotecnica e Ambien -tale, Università degli Studi di Napoli Federico II, Piazzale V. Tecchio,80 - Napoli, Italia.

(***) Institute of Geochemistry, Mineralogy and Mineral Resour -ces, Faculty of Science, Charles University in Prague, Albertov, 6 -12843, Prague, Czech Republic.

Geological features, technological characterization and weatheringphenomena of the Miocene Bryozoan and Lithothamnion limestones

(central-southern Italy)

ANNA CLAUDIA ANGRISANI (*), DOMENICO CALCATERRA (**), PIERGIULIO CAPPELLETTI (*), ABNER COLELLA (*), MARIANO PARENTE (*), RICHARD PRIKRYL (***) & MAURIZIO DE’ GENNARO (*)

17-10

Ital.J.Geosci. (Boll.Soc.Geol.It.), Vol. 130, No. 1 (2011), pp. 75-92, 14 figs., 9 tabs. (DOI: 10.3301/IJG.2010.25)

Queste bozze, cor rette deb bo no es serere sti tuite im med i at a mente alla Se g re te riadel la Società Geo log i ca Ital i a nac/o Di par ti men to di Scienze del la Ter raPi az zale Aldo Moro, 5 – 00185 ROMA

06 (17-10) ANGRISANI 75-92_GEOLOGIA 18/02/11 09.24 Pagina 75

76 A.C. ANGRISANI ET ALII

Fig. 1 - Examples of the use of Bryozoan and Lithothamnion Limestones: a) Roman columns and paved road of the archaeological site ofMinturno (Province of Latina); b) theatre (archaeological site of Minturno, Province of Latina) - CONSORZIO PER LA VALORIZZAZIONE DELPERLATO ROYAL CORENO, 2002; c) Santa Chiara Monastery’s bell tower (Napoli); d) Real San Ferdinando Bridge (Minturno, province of Latina - from: Manuale del perlato Royal Coreno); e) Montecassino Abbey (Province of Frosinone).


They overlie the Cretaceous limestones of the Abruzzi-Campania platform (BARBERA et alii, 1980), locally withthe interposition of a conglomeratic layer consisting ofCretaceous clasts (i.e. at Mt. Maggiore, VALLARIO, 1964)or of a few meters of Paleogene limestones (Cassino Plainand Mt. Porchio, ZALAFFI, 1963).

According to previous studies, the BLL Fm. wasreported as Langhian-Serravalian in age (ACCORDI et alii,1967; PAROTTO & PRATURLON, 1975; DAMIANI, 1990), butmore recent Sr-isotopic and biostratigraphic analysessuggest a Late Aquitanian to Early Tortonian age (CORDA& BRANDANO, 2003), at least for the outcrops in theLazio-Abruzzi area.

However, the BLL Fm. presents some characters thatare common to all the outcrop areas:

– a dominant lithology made by thick, generally mas-sive beds of bioclastic deposits;

– a macroscopically aspect imparted by closelyspaced anastomosing sub-horizontal stylolithic seams;

– a biogenic composition dominated by coralline redalgae, bryozoan colonies, mollusk shells, larger foraminifera(i.e. Amphistegina sp.) and echinoid remains, with minorcontribution by planktic foraminifers, serpulids and balanids(CARANNANTE, 1982).

The thickness ranges from 20-30 m in the Mt. Cam-posauro area (D’ARGENIO, 1961) to 100 m in the southernpart of Mt. Maio, close to Coreno Ausonio (ACCORDI, 1963).

Detailed sedimentological studies revealed that severallithofacies can be distinguished in the BLL on the basis oftheir rock fabric and relative abundance of the biotic com-ponents (BARBERA et alii, 1980; CIVITELLI & BRANDANO,2005). Many of these lithofacies correspond to commercialvarieties with different economic value (CONSORZIO PER

LA VALORIZZAZIONE DEL PERLATO CORENO, 2002).Nowadays in the Coreno Ausonio district (Frosinone

province, Lazio region) several quarries are active, produc-ing good quality material marketed in Italy and abroad.On the contrary the few quarries originally present in

Campania region (i.e., Cava Canale, Pietraroja, Benevento)were abandoned in the second half of the 1950’s, essen-tially for reasons of environmental preservation.

MATERIALS AND METHODS

The investigated samples were collected from twoquarry areas located at Coreno Ausonio (Cava La Valle-Frosinone province) and at Pietraroja (Cava Canale-Bene -vento province) (fig. 2). The selection of the former site isdue to the presence of all the commercial varieties; on thecontrary material from the latter site was studied for itshistorical importance, since it represents a stone used fora long time in the architecture of Campania region (Italy).

Oriented samples from unaltered blocks (approximatesize 100×50×50 cm) were taken. The specimens were thenreduced by diamond sawing and/or drilling to the shapeand size required by the specific tests.

The tests were performed at the Federico II Universitylaboratories in Naples and at the Institute of Geochem-istry, Mineralogy and Mineral Resources, Charles Univer-sity in Prague.

SEDIMENTOLOGICAL ANALYSIS

The sedimentological analysis was carried out on 37polished rock slabs, with a low magnification hand lens,and on 40 thin sections with an optical microscope. Eachsample was described by identifying the main componentsand the textural characters, according to the correspond-ing nomenclature (DUNHAM, 1962; EMBRY & KLOVAN,1971). Facies interpretation was performed with referenceto the facies model of CORDA & BRANDANO (2003).

MINERALOGICAL AND PETROGRAPHICAL ANALYSIS

Two sets of polished thin sections were used for theconventional optical microscopy and the cathodolumines-cence (CL) study, respectively. A third set of thin sections

GEOLOGICAL FEATURES, TECHNOLOGICAL CHARACTERIZATION AND WEATHERING PHENOMENA 77

Fig. 2 - Location of the main outcrop areas of the BLL.


was manufactured by filling the pore space (micropores,microcracks, open stylolites) with a mixture of low viscos-ity epoxy resin and fluorescent dye, following a proceduredescribed elsewhere (NISHIYAMA & KUSUDA, 1994;PRIKRYL, 2007). The microfacies description was per-formed by using a conventional optical microscope. Forthe CL study, a «cold» cathode attached to the petro-graphic LEICA DMLP microscope was used (apparatusCCL 8200 Mk4, working conditions 14-15 kV –300 µA).

X-ray powder diffraction analyses were performed byusing a Panalytical X’Pert PRO PW 3040/60 with X’celerator(working conditions: CuK� rad., 40 mA, 40 kV, scanspeed0.02° 2θ, time per step: 60 sec) on whole rock and insolubleresidue. Powders with grain size <10 �m were obtainedusing a McCrone micronizer mill. The milling allows se -veral problems to be overcome, such as particle statistics,primary extinction, microadsorption and preferred orienta-tion (KLUG et alii, 1974; BISH & CHIPERA, 1988). Quantita-tive results were obtained using the Reference IntensityRatio-RIR method (CHIPERA & BISH, 1995). The insolubleresidue was obtained by digesting the carbonates in a 3.7%diluted hydrochloric acid solution (Carlo Erba, HCl).

Major and trace elements were analysed on pressedpowder pellets with a Panalytical Axios fluorescence spec-trometer following the methods described by MELLUSO etalii (2005). Accuracy is generally ±1% for SiO2, TiO2, Al2O3,Fe2O3, CaO, K2O, MnO and ±4% for MgO, Na2O and P2O5.

PETROPHYSICAL PROPERTIES TESTING

The following physical properties were tested, accord-ing to the European-suggested standards (UNI EN) andISRM suggestions.

Specific gravity

Specific gravity was determined using a He-pycnome-ter (Multi Volume Pycnometer 1305 Micromeritics) withan accuracy of 0.1-0.2%. The test was carried out on fourcylindrical specimens (diameter = 21.6-22 mm; height<35 mm) for each lithotype. The measured apparent andreal volumes allowed the open porosity to be calculated.

Capillarity absorption

The amount of water absorbed in function of time(capillarity coefficient) was measured according to UNIEN 1925 suggested standards on a set of six 7.1 cm-sidedcubic specimens for each lithotype.

Water absorption by total immersion

The total absorbed water after immersion at roomtemperature and pressure was determined on the samespecimens used for the capillarity absorption. The testwas carried out following the UNI EN 13755 suggestedmethods on 7.1 cm-sided cubic samples.

Ultrasonic velocity tests

Ultrasonic tests were performed following the recom-mendations of UNI EN 14579 standards. The testingequipment was a Controls E 48 with a pair of 54 kHztransducers (diameter = 45 mm) in direct arrangement.To provide an adequate acoustic coupling between therock specimens and the transducers, a thin film of

hydrosoluble gel was used. To enhance energy transmis-sion, the transducers were firmly hand-pressed onto thespecimens. Measurements were taken on a set of thirty7.1 cm-sided cubic samples for each lithotype on all threepairs of sides of the specimens. P-wave velocity was deter-mined in both dry and wet conditions.

Uniaxial compressive strength

Uniaxial compressive strength (UCS) tests were car-ried out on ten 7.1 cm-sided cubic specimens for eachlithofacies previously used for the ultrasonic measure-ments. The tests were carried out according to the Euro-pean-suggested standards (UNI EN 1926). The testingdevice (Controls C5600 apparatus) allowed a maximumuniaxial load of 3000 kN; the axial load was increasedcontinuously at a rate of 0.5-1 MPa/s.

Flexural strength

Flexural strength was tested according to the UNI EN12372 standards on a set of three rock slabs (length =15 cm, width = 5 cm, thickness = 2.5 cm) only for the CavaCanale lithotype. The testing device was a Controls 65-L1300 apparatus with a maximum axial load of 25 kN.

Indirect tensile strength

Indirect tensile strength (Brazilian test) was evaluatedon a set of three cylindrical samples (diameter = 54mm;height = 21mm) for each Cava Canale lithotype following theISRM suggestions (ISRM, 1978). The testing device (WPMRavenstein equipment) allowed a maximum load of 100 kN;the load was increased continuously at a rate of 4 kN/min.

Abrasion resistance

Abrasion resistance was tested according to the UNIEN 14157 standards, on a set of three rock slabs (length =12 cm, width = 12 cm, thickness = 3 cm) only for CavaCanale lithotypes by using a Controls 48 D 0471 apparatus.

Rupture energy

Rupture energy was evaluated on a set of three rockslabs (length = 20 cm, width = 20 cm, thickness = 3 cm)only for Cava Canale specimens according to the Euro-pean-suggested standards (UNI EN 14158). The testingdevice was a Lonos test equipment.

AGEING TESTS

Ageing tests could be helpful to explain weatheringphenomena affecting the stone when used outdoor. Freeze-thaw tests were performed according to the UNI EN 12371standards on three 7.1 cm-sided cubic specimens for thelithotypes sampled both in Cava Canale and Cava La Valle.

The climatic chamber used for the freeze-thaw testswas a Binder MK 53. During the 20 freeze cycles the tem-perature decreased from 20°C to –12°C in six hours.

WEATHERING PHENOMENA CLASSIFICATION

The main weathering phenomena affecting the stonewere recognised through a detailed study on the façadesof the bell tower of the Santa Chiara monastery in the his-



torical town centre of Naples and were classified accord-ing to the NORMAL 11/88 standards.

The weathering of each bell tower facade was sur-veyed according to three grades of intensity: high, moder-ate, negligible. The extent of specific alteration was mea-sured in a semi-quantitative way in relation to the totalsurface area exposed (DE’ GENNARO et alii, 2000).

Moreover, a rock fragment sampled from the eastfaçade of the bell tower during a previous restoration wasanalysed under Scanning Electron Microscopy (SEM).These observations were performed with a Jeol JSM 5310apparatus equipped with an Oxford Inca Energy disper-sive X-ray Spectroscopy system (EDS).

RESULTS

SEDIMENTOLOGICAL ANALYSIS

Eight lithofacies were identified in the BLL of theCoreno Ausonio district and six in the Pietraroja one onthe basis of the textural characters, the relative abun-dance of the main biogenic components and the rhodolithdimension and shape as observed on polished rock slabsand in thin sections (figs. 3-4-5).

By integrating the sedimentological description withthe commercial classification used in the Coreno Ausoniodistrict, it was possible to correlate each lithofacies to aspecific commercial rock type as defined in the PerlatoRoyal Coreno Manual (CONSORZIO PER LA VALORIZ-ZAZIONE DEL PERLATO CORENO, 2002).

The main biogenic components are bryozoans (fig. 3a),corallinacean algae (fig. 3b), mollusk shells (fig. 3c) withminor contribution by serpulids and balanids. Largerbenthic foraminifers (i.e. Amphistegina sp. – fig. 3f,Gypsina sp. – fig. 4a, Elphidium sp. – fig. 4b, Heterosteginasp. – fig. 4c) and planktic foraminifers (figs. 4a-b-c) andechinoid remains (fig. 4d) are abundant in the matrix.According to the classification proposed by DUNHAM

(1962) and EMBRY & KLOVAN (1971) the recognised litho-types vary from rudstone to floatstone (tab. 1).


Rock type Figure Lithofacies(Embry & Klovan, 1971)

Main macroscopic characteristics

Porosity type (Choquette & Pray,

1970)Petrography

Perlato 5a Rhodolith rudstone Large rhodoliths (at least 10 cm in diameter) Fracture Porosity calcite, dolomite,

quartz

Mezza Perla 5b Rhodolith floatstone Smaller often distinctly elongated rhodoliths than in Perlato Fracture Porosity calcite, dolomite,

quartz

Perlatino 5c Rhodolith and oyster rudstone – floatstone

Small rhodoliths and abundant mollusks shells Fracture Porosity calcite, dolomite,

quartz

Risatino 6a Red algae and bryozoan grainstone – packstone Absence of large rhodoliths Fracture –

Intraparticle Porosity calcite, dolomite,

quartz

Botticino 6b Red algae and bryozoan rudstone Absence of rhodoliths Fracture Porosity calcite, dolomite,

quartz

Conchigliato 6c Bryozoan, coralline algae and mollusk shells rudstone

Rare and small rhodoliths and abundant mollusk shells Fracture Porosity calcite, dolomite,

quartz

Svirgolato 7a Bryozoan, oyster and red algae rudstone Abundant mollusk shells Fracture Porosity calcite, quartz

Nocciolato - Bryozoan, coralline algae and mollusk shells rudstone Abundant bryozoans Fracture Porosity calcite, quartz

TABLE 1

Sedimentological and petrographical characterization of the BBL from Cava Canale and Cava La Valle

TABLE 2

X-ray powder diffraction analysis – Cava Canale

Cava Canale

Lithofacies Sample Quartz (%) Calcite (%) Total (%)

Perlato C11CC 1 ± 1 101 ± 3 102 ± 4Mezza Perla C8-10CC 1 ± 1 99 ± 2 100 ± 3Perlatino C7-9CC 1 ± 1 99 ± 2 100 ± 3Botticino AD 1 ± 1 97 ± 2 98 ± 3Conchigliato C6CC 1 ± 1 97 ± 2 98 ± 3

TABLE 3

X-ray powder diffraction analysis – Cava La Valle

Coreno Ausonio

Litofacies Sample Quartz (%) Calcite (%) Total (%)

Perlato C1-5-6CA 1 ± 1 98 ± 2 99 ± 3Mezza Perla C3-C8-C15CA 1 ± 1 99 ± 2 100 ± 3Perlatino C4-C9-C10CA 1 ± 1 100 ± 3 101 ± 4Botticino C2CA 1 ± 1 101 ± 3 102 ± 4Risatino C12-C16CA 1 ± 1 99 ± 2 100 ± 3Nocciolato NCA 1 ± 1 98 ± 2 99 ± 3Conchigliato C7CA 1 ± 1 97 ± 2 98 ± 3Svirgolato C11CA 1 ± 1 98 ± 2 99 ± 3

TABLE 4

Insoluble residue of BLL from Cava Canale. Qz = quartz,Mt = montmorillonite (smectite), Kao = kaolinite, Il = illite,TiO2 = Ti-bearing oxide (rutile, anatase), Ab = feldspar (albite)

Insoluble residue

Lithofacies Sample Abundance Qz Mt Kao Il TiO Ab(%)

Perlato C11CC 0.33 x x x x x xMezza Perla C8-10CC 0.21 x x x x xPerlatino C7-9CC 0.19 x x x x xConchigliato C6CC 0.27 x x x x



Fig. 3 - Thin section photographs showing the main biogenic components of BLL: a) Thalli of coralline red algae encrusting bryozoans’remains (Perlatino-Cava La Valle); b) Nodular Bryozoan colonies (Conchigliato-Cava Canale); c) Pycnodontid oyster shell fragment (MezzaPerla-Cava La Valle); d) Serpulids and bryozoans (Perlato-Cava Canale); e) Balanid fragment (Svirgolato-Cava la Valle); f) Amphistegina sp.and echinoid spine (Perlato-Cava La Valle).


In detail, the Perlato commercial variety (fig. 5a) isa rhodolith rudstone in a bioclastic wackestone-pack-stone matrix and is characterized by the remarkabledimension of the rhodoliths (at least 10 cm in diame-ter). Mezza Perla (fig. 5b) is a rhodolith floatstone in abioclastic packstone matrix with smaller and oftenmore distinctly elongated rhodoliths than Perlato. Per-latino (fig. 5c) is a rhodolith and oyster rudstone-float-stone in a packstone matrix and is characterized bysmall rhodoliths and abundant mollusk shells. Risatino(fig. 6a) is a red algae and bryozoan grainstone-pack-stone with rare small rhodoliths. Botticino (fig. 6b) is ared algae and bryozoan rudstone in a bioclastic pack-stone matrix. Conchigliato (fig. 6c) is a bryozoan,coralline algae and mollusk shells rudstone with awackestone-packstone matrix. Svirgolato (fig. 7a) is abryozoan, oyster and red algae rudstone with a pack-stone matrix characterized by abundant fragments ofmollusk shells. Finally, Nocciolato is a bryozoan,

coralline algae and mollusk shells rudstone in a bioclas-tic packstone matrix characterized by the remarkabledimension of the bryozoans.

The thickness of the succession is 42 m at Cava LaValle and about 28 m at Cava Canale.

Among the lithofacies cropping out at Coreno Auso-nio, only those corresponding to the commercial varietiesPerlato, Mezza Perla, Perlatino, Botticino, Conchigliatoand Risatino were recognised also in the Campanianoutcrop of Cava Canale. The specimens from this out-crop exhibit the same texture and lithofacies charac-ters of the analogues of Coreno Ausonio. However,minor differences in the biogenic composition and inthe relative abundance of biogenic components weresometimes observed in a single lithofacies both in thesame locality and between the two sampled localities(fig. 8). Besides comparing the two logs (fig. 8) thelithofacies rarely occupied the same stratigraphicalposition.


Fig. 4 - Thin section photographs showing the main biogenic components of BLL: a) Gypsina sp. (Perlatino-Cava La Valle); b) Elphidium sp.(Svirgolato-Cava La Valle); c) Heterostegina sp. (Perlatino-Cava La Valle); d) Echinoid spine (Perlato-Cava La Valle).



Fig. 5 - Polished slabs and related thin sections of the BLL lithofacies: a) Perlato Classico (C1CA); b) Mezza Perla (C3CA); c) Perlatino (C9CA).


MINERALOGICAL AND PETROGRAPHIC ANALYSES

The cold cathodoluminescence microscopy enabledto recognise the calcitic cements filling the fractures andthe intraparticle voids of fossils (i.e., Coralline Red Algaeand bryozoans) for both Cava La Valle and Cava Canalespecimens.

Porosity was studied, for Cava Canale specimens, underUV-reflected light and classified according to the CHO-QUETTE & PRAY classification (1970). Porosity in the BLLstudied samples (tab. 1) is mainly represented by fractureporosity (fig. 9a) with minor contribution from intraparticleporosity, mainly in Risatino from Cava Canale (fig. 9b).

The X-ray powder diffraction pointed out the pres-ence of calcite and, in minor amount, quartz in all thelithofacies. Total amount of calcite ranges from about 97weight % to about 99 weight %. The insoluble residue,obtained only for Cava Canale samples, is essentially con-stituted by quartz and smectite, kaolinite, illite and rarelytitanium oxide and feldspar.

X-ray spectrometric analysis highlights the presence ofa minor amount of MgO in the Cava Canale (0.45-0.76%)samples than in the Cava La Valle ones (0.49-1.49%)(tabs. 5-6; fig. 10).

PETROPHYSICAL ANALYSIS

The petrophysical characterization was carried out onBotticino, Mezza Perla and Perlatino both from Cava Canaleand Cava La Valle and on Risatino sampled in Cava Canalebecause of its different macroscopic and microscopic char-acters that suggested different technical features.


TABLE 5

XRF chemical analysis – mean values for Cava Canale.ND means that the oxide is undetectable through the used

analysis method

Cava Canale – Major elements (%)

Lithofacies Perlato Mezza Perlatino Botticino Risatino ConchigliatoPerla

SiO2 0.73 0.44 0.33 0.65 0.44 0.27st. dev. 0.02 0.055 0.05 0.03 0.02 0.045

TiO2 0.02 0.02 0.01 0.02 0.02 0.01st. dev. 0.001 0.001 0.001 0.001 0.001 0.001

Al2O3 ND ND ND ND ND NDst. dev. – – – – – –

Fe2O3 0.12 0.06 0.04 0.10 0.09 0.03st. dev. 0.005 0.015 0.005 0.008 0.003 0.005

MnO 0.01 0.01 0.01 0.01 0.01 0.01st. dev. 0.001 0.001 0.001 0.001 0.001 0.001

MgO 0.65 0.46 0.47 0.76 0.74 0.59st. dev. 0.01 0.02 0.015 0.02 0.02 0.01

CaO 54.21 55.11 55.62 54.18 54.12 54.95st. dev. 1.2 1.905 1.375 1.35 1.6 1.705

Na2O 0.05 0.04 0.03 0.08 0.05 0.05st. dev. 0.001 0.001 0.005 0.001 0.001 0.001

K2O 0.05 0.04 0.02 0.06 0.03 0.02st. dev. 0.003 0.005 0.005 0.03 0.03 0.05

P2O5 0.62 0.74 0.14 0.21 0.10 0.15st. dev. 0.3 0.665 0.05 0.2 0.35 0.25

LOI 43.55 43.06 43.32 43.92 44.40 43.92

TOT 100 100 100 100 100 100

TABLE 6

XRF chemical analysis – mean values for Cava La Valle. ND means that the oxide is undetectable through the used analysis method

Cava La Valle – Major elements (%)

Lithofacies Perlato Mezza Perla Perlatino Botticino Risatino Conchigliato Svirgolato Nocciolato NC

SiO2 0.45 0.48 0.51 0.49 0.52 0.40 0.35 0.54 0.44st. dev. 0.045 0.095 0.035 0.025 0.085 0.055 0.02 0.05 0.07

TiO2 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02st. dev. 0.005 0.005 0.005 0.003 0.005 0.001 0.001 0.001 0.001

Al2O3 ND ND ND ND ND ND ND ND NDst. dev. – – – – – – – – –

Fe2O3 0.03 0.05 0.04 0.03 0.05 0.03 0.03 0.09 0.05st. dev. 0.005 0.005 0.005 0.008 0.001 0.015 0.005 0.005 0.005

MnO 0.01 – 0.01 0.01 – 0.01 – 0.01 0.01st. dev. 0.001 – 0.001 0.001 – 0.001 – 0.001 0.006

MgO 0.67 0.68 1.00 0.71 0.97 0.83 1.04 1.49 1.06st. dev. 0.19 0.115 0.02 0.04 0.09 0.02 0.01 0.015 0.03

CaO 54.92 55.19 55.09 54.67 54.92 55.17 55.88 53.81 53.95st. dev. 0.55 1.845 1.515 1.3 1.555 1.905 1.15 1.375 0.74

Na2O 0.04 0.03 0.05 0.03 0.04 0.03 0.05 0.08 0.04st. dev. 0.01 0.005 0.015 0.001 0.005 0.001 0.001 0.005 0.2

K2O 0.02 0.02 0.04 0.02 0.03 0.02 0.02 0.06 0.03st. dev. 0.005 0.005 0.004 0.05 0.005 0.005 0.002 0.005 0.015

P2O5 0.10 0.11 0.14 0.09 0.10 0.11 0.11 0.15 0.14st. dev. 0.025 0.01 0.01 0.25 0.004 0.55 0.3 0.055 0.005

LOI 43.74 43.41 43.10 43.94 43.35 43.39 42.52 43.76 44.28

TOT 100 100 100 100 100 100 100 100 100



Fig. 6 - Polished slabs and related thin sections of the BLL lithofacies: a) Risatino (C16CA); b) Botticino (C2CA); c) Conchigliato-Ghiandone (C7CA).


The main physical-mechanical parameters are givenin tabs. 7 and 8.

Specimens from both the sampling areas gave lowporosity, imbibition coefficient and capillarity absorptioncoefficient values. Risatino was characterized by thehigher values of these features.

All the UCS tests, performed considering the originalorientation of bedding, did not reveal any influence ofstrata orientation on the measured unconfined compres-sive rock strength.

The experimental data show that the UCS values for allthe three compared lithofacies (Mezza Perla, Perlatino andBotticino) are higher for the Cava La Valle samples thanfor the Cava Canale ones; the UCS variability range wasnarrower for Cava Canale specimens. Perlatino from boththe sampling areas has shown a wide range of variabilitywhile Botticino is constrained within a narrow range.Risatino from Cava Canale shows the smallest UCS values.

Dry and wet P-wave velocity did not reveal significantdifferences between the two provenance areas. The increasefrom dry to wet velocities was on the average of 3%.

The indirect tensile (Brazilian) strength average valuesof Mezza Perla, Perlatino and Botticino of Cava Canalevary from 9 to 9.8 MPa while the flexural strength onesrange from 11.5 to 12.3 MPa. Risatino was characterizedby the smallest average values of both these features.

The average abrasion resistance is about 16-17 mm,except for Risatino which shows a lower resistance to thistest but still higher than the reference sample.

Ultrasound velocity and uniaxial compressive strengthtests were also used to verify the resistance of the mate-rial after the ageing tests. The decrease of P-wave velo -city (fig. 11) and of UCS (fig. 12) measured after thefreeze-thaw cycles was of 5% and 8% respectively. Afterthe test the specimens rarely presented fractures or lossof material.

WEATHERING PHENOMENA AFFECTING THE BELL TOWER

OF THE SANTA CHIARA MONASTERY (NAPLES)

The main weathering phenomena affecting theBLL are well visible on all the above mentioned monu-

ments and in particular on the bell tower of the SantaChiara Monastery, which has been studied as a casehistory. These are essentially black crusts, efflores-cence, stain, detachment, scaling, and rarely exfolia-tion, pitting and vegetation (fig. 13). Integration (i.e.lacks filled up with different materials) and joints areoften observed.

The weathering of the northern, western and south-ern bell tower façades was moderate; on the contrary,the eastern facade showed a high decay probablybecause of its position facing a very trafficked street(tab. 9).

Finally, a small rock fragment (Mezza Perla) from theeast façade of the bell tower was analysed under Scan-ning Electron Microscopy. Results proved the presence ofa black crust on the surface of the sample characterizedby some alveoli (honeycombed shaped voids) (fig. 14a) inwhich it could be observed organic matter (Cyanobacteria– fig. 14b – and Diatoms – fig. 14c) and clay minerals(fig.14d), probably due to previous artificial treatmentson the material and/or presence of atmospheric particu-lates. The EDS analysis confirmed the presence of clayminerals whose composition is essentially made by silicaand allumina.

DISCUSSION

The results of sedimentological, mineralogical-petro-graphical and physico-mechanical analyses allowed todefine the properties of BLL that, although widelyemployed over several centuries, had never undergonesuch a systematic investigation.

The sedimentological study demonstrated that thecommercial varieties defined in the Coreno Ausonioquarrying district (CONSORZIO PER LA VALORIZZAZIONE

DEL PERLATO CORENO, 2002) correspond to differentlithofacies, defined on the basis of rock texture,rhodolith size, shape and orientation and relativeabundance of other biogenic components. The samelithofacies occur in both the studied sites, with only


Fig. 7 - Polished slabs and related thin sections of the BLL lithofacies Svirgolato-Fondomare (C11CA).



Cav

a C

anal

e

Roc

k ty

pe

Mez

za P

erla

P

erla

tino

Bot

ticin

oR

isat

ino

Spe

cim

ens

(no.

per

fa

cies

)m

in

mea

n m

ax

st. d

ev.

min

m

ean

max

st

. dev

. m

in

mea

n m

ax

st. d

ev.

min

m

ean

max

st

. dev

.

Dry

den

sity

(kN

/m3 )

30

26.0

1 26

.06

26.1

3 0.

005

25.8

2 25

.83

25.8

4 0.

001

25.9

0 26

.04

26.1

2 0.

010

25.3

4 25

.43

25.5

7 0.

010

Spe

cific

gra

vity

(kN

/m3 )

30

26.2

6 26

.31

26.3

7 0.

005

26.1

5 26

.20

26.2

5 0.

004

26.2

5 26

.47

26.6

0 0.

016

25.8

9 26

.29

26.6

7 0.

032

94.0 4

)%( ytisorop nep

O0.

951.

36

0.00

4 1.

26%

1.

411.

54%

0.

001

1.32

1.

651.

93

0.00

3 1.

95

2.40

3.20

0.

006

99.0 03

ssentcapmo

C0.

991

0.00

4 0.

98

0.99

0.99

0.

001

0.98

0.

990.

99

0.00

3 0.

96

0.97

0.98

0.

008

Imbi

bitio

n co

effic

ient

(%)

6 0.

31

0.37

0.44

0.

056

0.42

0.

450.

48

0.02

7 0.

21

0.25

0.32

0.

045

0.69

1.

101.

54

0.30

8

Cap

. Abs

orpt

ion

(g/c

m2 *s

0,5 )

6 3.

33E

-05

4.78

E-05

6.98

E-0

51.

38E

-05

5.09

E-0

55.

65E-

056.

06E

-05

3.69

1E-0

62.

78E

-05

3.37

E-05

3.83

E-0

53.

79E

-06

1.88

E-0

41.

97E-

042.

09E

-04

8.39

E-0

6

P-w

ave

dry

velo

city

(m/s

) 30

56

23

6113

6411

19

8.37

52

75

6057

6291

17

2.43

56

53

6090

6351

17

8.54

49

64

5495

5856

25

1.24

P-w

ave

wet

vel

ocity

(m/s

) 30

61

71

6298

6454

88

.88

6170

62

3763

49

66.4

2 61

06

6221

6364

99

.03

5472

57

2558

82

126.

18

Un.

com

pres

sive

stre

ngth

(MP

a)10

14

5 16

017

4 10

.9

126

161

188

25.1

17

5 18

218

7 5.

4 14

5 16

217

2 10

.9

Indi

rect

tens

ile s

treng

th (M

Pa)

3

6.9

9.8

11.1

1.

8 8.

8 9.

810

.8

0,8

8 9

10.7

1

5,9

7,2

8,2

0.1

Flex

tura

l stre

ngth

(MP

a)

3 9.

53

12.3

014

.77

2.15

1 3.

59

11.5

016

.08

5.61

3 7.

65

11.9

815

.85

3.34

9 7.

65

9.40

11.2

4 1.

466

Abr

asio

n re

sist

ance

(mm

) 3

15.8

8 16

.81

17.6

3 0.

817

16.1

3 16

.94

17.8

8 0.

715

15.8

8 16

.88

17.8

8 0.

884

16.8

8 18

18.8

8 0.

893

Rup

ture

ene

rgy

(J)

3 3.

43

3.76

4.41

0.

462

2.94

3.

113.

43

0.23

1 1.

96

2.65

3.43

0.

588

3.43

4.

094.

41

0.46

2

TABLE7

Petrophysical Characterization

– Cava Can

ale

Cav

a La

Val

le

Roc

k ty

pe

Mez

za P

erla

P

erla

tino

Bot

ticin

oS

peci

men

s(n

o. p

er fa

cies

)m

in

mea

n m

ax

st. d

ev.

min

m

ean

max

st

. dev

. m

in

mea

n m

ax

st. d

ev.

Dry

den

sity

(kN

/m3

28.52 03

)25

.88

25.9

2 0.

004

25.7

9 25

.92

26.0

6 0.

012

25.8

7 25

.94

25.9

9 0.

005

Spe

cific

gra

vity

(kN

/m3

12.62 03

)26

.33

26.4

4 0.

010

26.2

4 26

.30

26.3

6 0.

006

26.1

6 26

.25

26.3

0 0.

005

82.1 4

)%( ytisorop nep

O1.

692.

35

0.00

4 0.

91

1.44

2.08

0.

005

0.92

1.

191.

52

0.00

2 89.0

03 ssentcap

moC

0.99

0.99

0.

004

0.98

0.

990.

99

0.00

5 0.

98

0.99

0.99

0.

002

Imbi

bitio

n co

effic

ient

(%)

6 0.

48

0.56

0.70

0.

083

0.61

0.

660.

72

0.05

0 0.

47

0.50

0.54

0.

026

Cap

illar

ity a

bsor

ptio

n (g

/cm

2 *s0,

5 ) 6

5.15

E-0

5 6.

79E-

059.

71E

-05

1.80

E-0

57.

12E

-05

7.84

E-05

9.48

E-0

59.

51E

-06

6.05

E-0

56.

82E-

057.

72E

-05

7.57

E-0

6P

-wav

e dr

y ve

loci

ty (m

/s)

30

5868

61

3763

13

119.

48

5966

61

4163

21

94.5

0 51

17

6010

6357

23

4.38

P

-wav

e w

et v

eloc

ity (m

/s)

30

6237

63

3764

27

55.6

6 62

32

6311

6436

63

.35

5842

62

1964

14

155.

64

Uni

axia

l com

pres

sive

stre

ngth

(MP

a)

10

139

196

245

40.4

13

8 18

825

0 48

.2

153

205

252

30.5

TABLE8

Petrophysical Characterization

– Cava La Valle


minor differences in the relative abundance of the bio-genic components. This indicates that the CorenoAusonio and the Pietraroja area experienced very simi-lar paleoenvironmental conditions during the deposi-tion of the BBL. All the lithofacies recognized at CavaLa Valle and at Cava Canale can be referred to the mid-dle sector of a carbonate ramp, according to the depo-sitional model proposed for the BLL by CORDA &BRANDANO (2003). This paleoenvironmental interpreta-tion is confirmed by the available water-depth indica-tors like the rhodolith shape, growth structure and tax-onomic composition (BRANDANO et alii, 2007) and themorphology of amphysteginid tests (MATEU-VICENS etalii, 2009).

On the other hand, a comparison of the stratigraphiclogs of the Cava La Valle and Cava Canale quarriesreveals that the lithofacies do not occur in the samestratigraphic order in both the localities. This is eitherdue to the scarce lateral continuity of the depositionalsystem of the BBL, largely controlled by the inheritedmorphology of the substrate, and/or to slight differences

in the age of the stratigraphic interval represented by theBBL in the two studied localities.

The analytical results confirmed the homogeneousmineralogical and chemical composition of the stone; theonly difference between the two sampling areas is thelarger amount of MgO in the Cava La Valle samples. Thisdifference could be useful during restoration of historicalbuildings to identify the provenance of the employed BLL.


Fig. 8 - Lithological logs for the sites of Cava La Valle (FR) and Cava Canale (BN): M, mudstone; W, wackestone; P, packstone; G, grainstone;F, floatstone; R, rudstone. The relative abundance of the biogenic components and the occurrence of particular taxa of red algae and foraminifersare shown in the table on the right.

TABLE 9

Weathered area of the façade of the bell tower of Santa Chiara Monastery

Façade Weathered area (%) Intensity

Northern 49.59 ModerateWestern 34.19 ModerateSouthern 38.56 ModerateEastern 70.88 High


The main index properties of the BLL are comparableto the ones of other sedimentary rocks widely employedas ornamental stones throughout the architectural historyof the Campania region (Breccia Irpina, Marmi di Mon-dragone, Marmi di Vitulano, Pietra di Bellona, Pietra diPadula - ALLOCCA et alii, 2010).

Contrary to the existing literature (LATHRAM & THIEL,1946; PRIKRYL, 2001; TÖRÖK, 2006) results from physi-cal-mechanical tests demonstrated no evident relationsbetween the lithological and the technical features ofthe BLL.

In fact, as regards apparent density and bulk den-sity values are similar for all the lithofacies from boththe outcrops. For each lithofacies the differencesbetween apparent density and bulk density values arealso very small: this reflects the generally very lowporosity values. Risatino from Cava Canale showsthe highest values of open porosity, imbibition andcapillarity absorption coefficient, probably due to thecontribution of intraparticle porosity observed underUV-reflected light.

BLL from both the sites showed good performance interms of mechanical strength, as confirmed by the UCStests and by the ultrasonic velocities. As a consequence,the range of values allows this rock to be defined as ahigh strength rock (COATES, 1964; DEERE & MILLER,1966; BIENIAWSKI, 1973; BROCH & FRANKLIN, 1972;IAEG, 1979; ISRM, 1981).

The similar UCS values measured both along verso(parallel to the stratification) and contro (perpendicularly tothe stratification) – DE’ GENNARO et alii, 2000; PAPAMICHOS

et alii, 2006 – demonstrate that the mechanical behaviour ofthe material is primarily influenced by the 3D-arrangementof the joints that pervasively transect the rock.

The experimental physical-mechanical data show thatthe UCS values for all the three compared lithofacies(Mezza Perla, Perlatino and Botticino) are higher for theCava La Valle samples than for the Cava Canale ones,while open porosity is similar for both the sites, showingin this case no evident relation with lithofacies. Risatinofrom Cava Canale gave the lowest UCS values, in accor-dance with the highest open porosity values.

The narrower UCS variability range for the CavaCanale specimens demonstrated the greater homogeneityof these lithotypes; Botticino from both sites remainswithin a narrow range probably because of the rare pres-ence of rhodoliths and stylolithic surfaces.

The difference in the UCS values between the twoareas could be linked to the presence in the Cava Canalesamples of calcite-filled microfractures, well visible incold cathodoluminescence microscopy; these microfrac-tures could act as preferential weakness lines, even if theydo not contribute significantly to open porosity. Besides,the higher UCS values of Cava La Valle samples could bepartly due to the major concentration of MgO (ALLOCCA,2007; VOLA, 2009).

As regards the remaining tests, the following pointscan be highlighted:

– flexural strength was influenced especially by thepresence of fractures and mollusk shells arranged parallelto the application of the load;


Fig. 9 - BLL porosity in thin section under UV-reflected light: a) stylolite seams (Botticino - Cava Canale); b) bryozoans and coralline red algaefragments (Risatino - Cava Canale).

Fig. 10 - MgO and CaO concentration in Cava Canale and Cava LaValle samples.


– abrasion resistance and rupture energy valuesproved the disposition of the material for paving;

– ageing tests show a decrease of the main technicalfeatures of the stone (P-wave velocity and UCS) after thefreeze-thaw cycles. However, the rock must be classifiedas frost-proof.

Finally this research work enabled to remark that themost common weathering phenomena affecting the stone areblack crusts and efflorescences, the most typyical weatheringfeatures for limestones (TÖRÖK, 2003; TÖRÖK et alii, 2007).Fractures and detachments, probably due to the dissolutionand the breaking along the calcite-filled fractures, are oftenobserved (i.e. S. Chiara Monastery bell tower, Naples) asclearly emphasized through optical microscopy.

CONCLUSIONS

The present study brings new data on the sedimento-logical-stratigraphical, mineralogical-petrographical and

engineering-geological characters of the BLL Fm. and onthe main weathering phenomena involving the stonewhen used outdoor. The paper discusses also the influ-ence of rock fabric, chemical composition, presence andarrangement of fractures and stylolithes on the technicalfeatures of the stone. This approach could produce infor-mation relevant to the decision of the most appropriatecommercial use of the different lithofacies and commer-cial varieties.

The sedimentological analysis allowed distinguish-ing of eight lithofacies corresponding to as many com-mercial rock types in the BLL Fm. It is worth mention-ing that the correspondence established in this paperbetween the lithofacies of the BLL and the commercialvarieties of the Perlato Royal Coreno disclosed somevery interesting perspectives. In fact, like any faciesmodel (WALKER, 1992), the BLL depositional model(CORDA & BRANDANO, 2003; CIVITELLI & BRANDANO,2005) can be used to make predictions on lithofaciesdistribution. This could be of great value inasmuch as it


Fig. 11 - P-wave velocity before (v0) and after (v20) 20 freeze-thaw cycles for both Cava Canale (CC) and Cava La Valle (CA) samples.

Fig. 12 - UCS before (UCS0) and after (UCS20) 20 freeze-thaw cycles for both Cava Canale (CC) and Cava La Valle (CA) samples.



Fig. 13 - Weathering phenomena of thebell tower of Santa Chiara monasteryexpressed in percentage of involvedsurface.

Fig. 14 - SEM micrograph: a) black crust; b) Cyanobacteria; c) Diatoms; d) clay minerals.


would allow using the extensive sedimentological-strati-graphical literature on the BLL to optimize the explo-ration both of mature quarrying districts and of areasthat have not yet been intensively exploited. In particu-lar it would be possible to evaluate the economic poten-tial of new areas by predicting the volume and distribu-tion of the most valuable varieties. However, the factthat the two studied localities, despite they share thesame paleoenvironmental setting, show differences inthe vertical distribution of the lithofacies suggest thatdetailed stratigraphic studies are needed in order todefine accurately the vertical and lateral distribution oflithofacies, and commercial varieties, in each area ofpotential interest.

Mineralogical and petrographical studies did notreveal significant differences between the two samplingsites. However, a greater content of MgO was detected inthe Cava La Valle specimens. This information could behelpful to identify the provenance of the BLL used asdimension stone in historical buildings and could partlyinfluence some technical features of the stone such asthe UCS.

On the contrary, physico-mechanical tests demon-strated a difference between the Cava La Valle and theCava Canale samples. Although open porosity is similarfor both the sites, UCS values are higher for the Cava LaValle samples. This difference could be due to the calcite-filled microfractures present in the Cava Canale samplesthat could act as preferential weakness lines, even if theydo not contribute to open porosity.

The similar UCS measured both along verso andcontro demonstrate that the mechanical behaviour ofthe material is primarily influenced by the spatial distri-bution of the fractures/joints that go through the rockpervasively.

However, the overall results of the physico-mechani-cal tests demonstrated that no evident relation betweenthe lithological and the technical features of the stone canbe univocally found.

In addition, the ageing tests suggested that althoughresistant to freeze-thaw action the stone could be affectedby weathering when used outdoor.

Finally, it must be emphasised that the BLL fromboth sites showed good performance in terms of mechani-cal strength, abrasion resistance and rupture energy. Itevidently implies that the rock could be successfullyemployed for street furniture and/or with architecturaland structural purposes as confirmed by its historical andpresent-day uses.

ACKNOWLEDGEMENTS

The authors are grateful to Prometeo s.r.l. and Sant’AnnaMarmi Coreno s.n.c. for supplying the samples and to Angelo Urgeraand Marco Brandano (University of Rome «La Sapienza») for theirhelpful suggestions. This work was carried up within the scientificactivities of the Centro Regionale di Competenza «INNOVA». Partof geomechanical tests were financially supported by the researchproject of the Ministry of Education, Youth and Sports of theCzech Republic: MSM 0021620855 ‘Material flow mechanisms inthe upper spheres of the Earth’. The staff of the laboratory of rockphysical properties of the Institute of Geology, Academy ofSciences of the Czech Republic (namely Mr. Zdenek Erdinger andMrs. Julie Erdingerová) is acknowledged for help with rockmechanical tests. Dr. Aneta Št’astná kindly introduced Anna Clau-dia Angrisani to the method of CL microscopy. Thanks are also dueto R. de Gennaro (CISAG, Federico II University of Naples) fortechnical support during SEM-EDS analyses.

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Manuscript received 19 May 2010; accepted 30 September 2010; editorial responsability and handling by S. Conticelli.


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