The building stones of the ancient centre of Naples (Italy): Piperno from Campi Flegrei. A contribution to the knowledge of a long-time-used stone

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ThebuildingstonesoftheancientcentreofNaples(Italy):PipernofromCampiFlegrei.Acontributiontotheknowledgeofa...

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Journal of Cultural Heritage 1 (2000) 415–427© 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved

1296-2074(00)01097-9/FLA

The building stones of the ancient centre of Naples (Italy):Piperno from Campi Flegrei. A contribution to the

knowledge of a long-time-used stone

Domenico Calcaterraa, Piergiulio Cappellettib, Alessio Langellac*, Vincenzo Morrab,Abner Colellab, Roberto de Gennarob

a Dipartimento d’Ingegneria Geotecnica, Universita Federico II, Piazzale V. Tecchio 80, Naples, Italyb Dipartimento di Scienze della Terra, Universita Federico II, Via Mezzocannone 8, Naples, Italy

c Facolta di Scienze, Universita del Sannio, via Port’Arsa 11, Benevento, Italy

Received 19 April 2000; accepted 23 August 2000

Abstract – Piperno, a Late Quaternary magmatic rock cropping out on the eastern side of the Campi Flegrei (Italy), isprobably the most important building stone of Naples, used over a time-span from at least the Roman age until thebeginning of the 20th century. Despite its wide diffusion in the monumental architecture of Naples, very little is knownabout this rock, as regards its technical features, as well as the geological aspects. This paper aims at providing a firstoverall contribution towards a rediscovery of this long-time-used material, in view of careful restoration works, whichnowadays at Naples only take into account the proper geological features of the stone in a few peculiar cases. Thus, itseems of extreme importance to understand the basic parameters of Piperno and, above all, its response to weatheringagents. Main mineralogical, petrographical and engineering–geological properties are presented here for the first time, withspecific reference to two sampling areas, located at Pianura and Soccavo, in the western sector of the Neapolitan urbanarea. As far as many of its physico–mechanical features are concerned, Piperno extends over a wide range of values, whichallow different varieties of the rock to be identified. This preliminary result is seemingly in accordance with data from oldhistorical literature, which stated the existence of six horizons in the Piperno formation. © 2000 Editions scientifiques etmedicales Elsevier SAS

Keywords: building stone / geological features / Campi Flegrei / Italy / Piperno / weathering

1. Introduction

Surveying and mapping of the building stonesused in the ancient city centre of Naples (Italy)allowed their distribution as well as the specificweathering grade to be assessed [1, 2]. The mostcommon building stones proved to be the Neapoli-tan Yellow Tuff (NYT) and the Piperno, both prod-ucts of Campi Flegrei emplaced in the LateQuaternary. Despite their importance in Neapolitanarchitecture, geological knowledge of NYT and

Piperno is definitely different. In fact, the wide-spread diffusion of NYT over the Neapolitan areaand in the eastern sector of Campi Flegrei deeplyinvolved this material in anthropical activities. NYThas, therefore, been widely studied, with a numberof contributions published over the last few decades,covering almost all the aspects of scientific interest(origin and nature of the formation, geomechanicalproperties, weathering features etc.). Furthermore, italso represents a relevant material from a technolog-ical point of view due to its particular mineralogicalcomposition.

On the other hand, Piperno is still an ‘obscure’material, notwithstanding its intensive use in

* Correspondence and reprints:E-mail address: [email protected] (A. Langella).

D. Calcaterra et al. / J. Cult. Heritage 1 (2000) 415–427416

Neapolitan architecture between the 13th and 19thcenturies. Several reasons can account for this situa-tion: first of all, the limited extension of the out-crops, and its better physico–mechanical featureswith respect to NYT. Much attention was devotedto volcanological and geological aspects concerningthis material over the last three centuries. However,no data are available in terms of mineralogical,petrographical and physico–mechanical propertiesconcerning the use of this material as a buildingstone.

The aim of the present research was to fill thisgap, defining some useful parameters that enablePiperno sensu strictu to be carefully distinguishedfrom other piperno-like materials (pipernoid tuffs,piperno sensu lato) coming from different volcanicformations and outcrops, and, in the meantime, tounderstand the behaviour of this stone when ex-posed to weathering agents.

2. Previous geological studies on Piperno

Piperno is the most well-known magmatic rock inCampi Flegrei. This lithotype is exposed at thenorthern and southern foot of Camaldoli Hill, atPianura and Soccavo (Torre Franco and Verdolino).The term ‘Piperno’ probably derives from the Latinpiperinus used by Romans to indicate a particularkind of volcanic rock ‘lapis piperinus, seu albiduscum punctuis nigris, durus atque fortissimus’ [3].

The only documented quarries are located in theabove-cited areas of Campi Flegrei and are formedby tunnels branching under the hill [4, 5]. Theformation seems to gently dip northward, but itsbase is not exposed; however, whenever visible,thickness is about 20 m [6].

The origin and age of this deposit are still de-bated. The occurrence of the scoriae, called fiammeby von Buch [7], led some authors to a very com-plex interpretation of the depositional mechanism asa lava flow. Since the beginning of this centurymany researchers have addressed their attention tothis typical deposit in order to find an answer to thePiperno ‘question’. Dell’Erba [8] and Zambonini [9]related Piperno to a high temperature ‘pyroclasticcloud’; De Lorenzo [10] defined it as a trachyticschlieren-lava; Rittmann [11] and Gottini [12] re-lated it to a lava-lake activity. Fisher and Schmincke[13] considered the deposit as a welded fallout tuff(agglutinate); Rosi et al. [6] defined Piperno as apyroclastic flow deposit resulting from a substainedactivity. In the last years, some authors have differ-ently interpreted Piperno in a wider volcanologicalcontext.

It is useful to remember that in Campi Flegrei(mainland and island of Procida) many pyroclasticsequences, known as ‘breccias’ crop out. These de-posits are present on Procida island, Monte di Pro-cida, Cuma, Licola, Quarto, Soccavo (CamaldoliHill) and Naples (Ponti Rossi). Rosi et al. [6] inter-preted these deposits as proximal breccias of theCampanian Ignimbrite, thus hypothesizing CampiFlegrei as the source of this huge eruption [14]. Thisconclusion is also supported by 39Ar/40Ar dating. Infact sanidine from both Campanian Ignimbrite andsome western breccias yielded a common age of37 000 years [6].

This interpretation was questioned by other au-thors. Di Girolamo et al. [15], Lirer et al. [16] andMelluso et al. [17], also on the basis of 14C dating ofpaleosoils (22 000 years) occurring at the bottom ofwestern breccias, considered them as deposits re-lated to local vents. However, these controversialhypotheses are overrun by recent petrologic andradiometric data that indicate similarities betweenthese breccias and the deposit of Campania Ign-imbrite (Ricci, Ph.D. thesis in progress).

Field features are also debated. De Lorenzo [10]described two layers of Piperno interspersed bybreccia layers. Maggiore [18] accurately describedsix layers characterized by very different technicalproperties. These layers have been exploited overdifferent ages. Rosi et al. [6] identified four layers ofeutaxitic tuff, interspersed by loose lithic-rich brec-cia beds. At this time the outcrops are barely acces-sible and the entrance to the underground quarriesare almost hidden.

3. Materials

Sampled materials come from two outcrops lo-cated at Pianura and Soccavo at the foot of theCamaldoli hill, the highest peak of the entire Phle-graean area (figure 1). Such outcrops, close to theentrance of the old underground quarries, are barelyaccessible at present.

A fundamental contribution of the first half ofthis century reports that these quarries exploited atleast five out of six layers of Piperno and that thephysical features of each layer were substantiallydifferent [18]. Therefore, it was attempted to collectsamples that differed at least from a macroscopicalpoint of view, as it was impossible to identify theoutcrops of these different layers.

Figure 1 and table I report the location of thesampling areas and a short description of thematerials.

D. Calcaterra et al. / J. Cult. Heritage 1 (2000) 415–427 417

Figure 1. Sketch map of Camaldoli Hill (Naples, southern Italy) with the location of the sampling areas. (a) Pianura; (b)Soccavo.

D. Calcaterra et al. / J. Cult. Heritage 1 (2000) 415–427418

Table I. Sampling locations and macroscopical features of Piperno samples from Pianura and Soccavo

Location Description

Pianura Quite homogeneous material characterized by a light grey matrix and very small collapsed fiamme(max. 7–10 cm)

Very heterogeneous material with a variable matrix generally similar to Pianura samples but, inSoccavosome cases, dark grey or reddish. In the latter case, a great amount of xenoliths (max. 1 cm) isrecorded. Generally, grey or reddish samples are characterized by very large fiamme (30–40 cm)that in some areas represent more than 90 % in volume.

For all laboratory samples, all traces of weather-ing were removed and, according to the needs of thevarious testing methodologies, various sets of sam-ples were obtained:� pycnometer tests (cylindrical specimens: diame-

ter=21.6–22 mm; height B35 mm);� capillarity absorption tests (diameter 58 mm;

variable height);� water absorption by total immersion (diameter

58 mm; variable height);� water vapour permeability (diameter 58 mm;

variable height);� ultrasonic and uniaxial compressive tests (71

mm-sided cubic samples);� point load tests (prismatic samples; height=

17.5–38.5 mm; width=37–74 mm).

4. Methods

4.1. Mineralogical characterization

Mineralogical characterization was carried outboth by means of XRPD (X-ray powder diffraction)analysis (Philips PW1730/3710) and SEM observa-tion (JSM 5310). Chemical composition of the dif-ferent crystal phases was obtained by EDS-WDSmicroprobe analyses (CAMECA SX50).

Quantitative mineralogical analyses were per-formed by XRPD on two representative samplesusing a Cu Ka radiation, incident- and diffracted-beam Soller slits, curved graphite crystal monochro-mator, 2u range from 3 to 100°, step size 0.02° 2uand 10 s counting time per step. An internal stan-dard, a-Al2O3 (1 mm, Buehler Micropolish), wasadded to each sample in amounts of 20.0 wt.%.

Powders with grain size B10 mm were obtainedusing a McCrone micronizer mill; such a particlesize allows several problems to be overcome, suchas: particle statistics, primary extinction, microad-sorption and preferred orientation [19, 20].

Powder data sets were analysed using the Rietveldmethod [21] with a GSAS package [22]; startingatomic coordinates of the structure were taken fromthe literature: sanidine [23], albite [24], diopside[25], biotite [26], magnetite [27] and sodalite [28].

4.2. X-ray fluorescence spectrometry (XRFS)

Major and trace elements were analysed at Napleson pressed powder pellets with a Philips PW1400X-ray fluorescence spectrometer, following themethods described by Melluso et al. [17]. Thirty-fiveinternational standards were used as calibrationanalyses. Precision is generally within 1 % for SiO2,TiO2, Al2O3, Fe2O3t and CaO, better than 6 % forK2O, 90.03 wt.% for MnO and P2O5, generallybetter than 5–10 % for all trace elements in theobserved compositional ranges. Na and Mg werealso analysed by atomic absorption spectrophotome-try (AAS). Typical precision is better than 2 % forMg and better than 6 % for Na.

4.3. Specific gravity

Specific gravity was determined with a He-pyc-nometer (Micromeritics Multivolume Pycnometer1305), with an accuracy of 90.1–0.2 %. Given thehigh heterogeneity of the material, the test wascarried out on a large number of samples (about100) and, for each of them, at least three measureswere performed. The measured apparent and realvolumes allowed the open porosity to be calculated.

4.4. Capillarity absorption

The amount of water absorbed as a function oftime was measured according to the Italian-sug-gested standard reported in NORMAL 11/85. Speci-mens used for this test [29] had a cylindrical shapeand a surface (s)/apparent volume (v) ratio of 1cm−1Bs(cm2)/v(cm3)B2 cm−1. Each series ofspecimens (three) was previously chosen on the basis

D. Calcaterra et al. / J. Cult. Heritage 1 (2000) 415–427 419

of similar macroscopical features in order to givehomogeneous results. The capillarity absorption co-efficient was the following: Mt (g/cm2·s1/2).

4.5. Water absorption by total immersion

The total absorbed water after immersion indeionized water at room temperature and pressurewas evaluated on the same specimens (21) as usedfor capillarity absorption. The imbibition capacity isgiven by the following ratio: Mmax–Mf/Mf · 100,where Mmax is the weight (g) of the sample at theend of the test and Mf is the weight of the driedsample. The procedure follows NORMAL 7/81[30].

4.6. Water vapour permeability

Water vapour permeability is the water vapourflowing in a time unit through two parallel faces ofa body with a constant thickness, under a differenceof water vapour partial pressure at constant temper-ature (20 °C) [31]. If measurements are made at adifferent temperature, a correction should be oper-ated; the permeability is expressed in g/m2· 24 h.This test was also carried out on at least threespecimens for each series (in total 18).

4.7. Ultrasonic tests

Ultrasonic tests were carried out according toItalian-suggested standards [32], also taking intoaccount international recommendations [33].Sawcut samples were washed with deionized water.A PUNDIT (CNS Instruments Ltd.), ultrasonic non-destructive digital tester was used with a pair of24-kHz transducers, in direct arrangement (i.e.transmitter and receiver positioned on oppositesides). Ultrasonic pulses were read out on the digitaldisplay, to an accuracy of 90.1 ms. To provide anadequate acoustic coupling between the rock speci-men and the transducers, a thin film of hydrosolublegel was used; to enhance energy transmission, thetransducers were firmly hand-pressed onto the speci-mens. Measurements were taken on all three pairsof sides of the cubic samples. The compressive wavevelocities were determined in both dry and water-saturated conditions. The set of dry measurementswas performed after oven-drying the samples at50°C and overnight cooling in dehumidified atmo-sphere until a constant weight was reached. Thesaturation was accomplished by immersion in deion-ized water until constant weight was reached and, inany case, for at least 10 days. Before both test series,

rock density was also determined. Forty-three sam-ples from Soccavo and 33 from Pianura wereanalysed.

4.8. The uniaxial compressive strength

Uniaxial compressive strength (UCS) tests werecarried out on some of the specimens previouslyused for the ultrasonic measures. AGI [34] sugges-tions were followed, even though the tests wereperformed on cubic samples. Before each test, rockdensity was determined. The testing device (Gald-abini PMA60 apparatus) allowed a maximum axialload of 600 kN. The axial load was increasedcontinuously at a rate within the limits of 0.5–1.0MPa/s. Axial strain was measured for all specimens,by means of two linear transducers; diametricalstrain was determined for two samples, in each caseusing four strain gauges. Load and strain were con-tinuously registered by an automatic data logger;sampling time interval was between 80 and 120 ms.Thirty tests were carried out on samples from Soc-cavo and ten from Pianura.

4.9. Point load strength

Point load strength (PLS) tests were carried outusing a portable device (Controls D550) and com-plied with the established procedures [35], especiallyas regards the ‘factoring’ of the strength results, inorder to obtain a normalized value (Is50). Each PLSresult (21 from Soccavo, 26 from Pianura) repre-sents the average of at least five crush tests.

5. Results and discussion

The results of minero–petrographical and physico–mechanical investigations so far obtained have al-lowed us to define the properties of Piperno which,even though widely employed over several centuries,had never undergone such a systematic characteriza-tion.

5.1. Mineralogical and petrographical features

Piperno is characterized by a eutaxitic texturewith black flattened scoriae ( fiamme) set in a light-grey matrix. Similar textures can be seen on amicroscopic scale with tiny shards flattened andmoulded one over another.

At the macroscopic scale Piperno shows centime-ter- to decimeter-sized fiamme set in a hard, greymatrix (figure 2). The fiamme show a maximum

D. Calcaterra et al. / J. Cult. Heritage 1 (2000) 415–427420

Figure 2. Specimens of Piperno showing the typical eutaxitic texture. Samples from Pianura (a) and Soccavo (b). Samplesize: 71 mm.

length of 30–40 cm and an average flattening ratioof 1:10.

The main phases are sanidine (Or68–43), subordi-nate plagioclase (An86–28), clinopyroxene rangingfrom diopside to salite (Mg85–47), biotite, amphibole(Mg62–56), magnetite (ulv40–37) and sodalite. Thesephases are set in a totally recrystallized matrix,where alkali feldspar (Or53–34) represents the ne-oformed phase. Figure 3 shows the typical eutaxitictexture of Piperno; an euhedral alkali feldspar phe-nocryst is present at the centre of the section. Fi-amme are also recrystallized by tiny new crystals ofalkali feldspar with the same composition as thoseof matrix.

The fiamme have a composition ranging fromtrachyte to trachyphonolite (SiO2=60.9–63.5wt.%; K2O=6.8–7.3 wt.%; on dry basis). No widecompositional differences were noted for Pipernosampled in different localities (Soccavo and Pia-nura). In some cases it shows a peralkaline character(A.I.=agpaitic index, up to 1.14). Minor elementsshow a restricted range in concentration; Nb and Zrexhibit their incompatible characteristics and con-centrations ranging from 90 to 121 ppm and 581 to713 ppm, respectively; Sr and Ba exhibit low con-centrations (from 40 to 22 ppm and from 54 to 18ppm, respectively). All these geochemical featuresare typical of the very differentiated rocks of CampiFlegrei and testify to the residual character ofmagma that produced the Piperno deposit.

The features of Piperno are related not only towelding phenomena, but also to vapour phase crys-tallization. In a general way this process takes placeas the volcanic deposit ‘cooks in its own juices’ [36].Vapour phase crystallization results from hot gasespassing up through the body of the deposit. Somegas may be juvenile exsolved from pumice and vitricparticles, and some may be from heated groundwa-ter. This process leads to significant lithologicalchanges. Large glassy fiamme loose their characterand become a hard mass, as does the matrix thatbecomes hard and compact. This process forms a

Figure 3. Polarizing microscope photograph of an euhe-dral crystal and tiny authigenic alkali-feldspars within ascoria ( fiamma). Crossed nicols, 40× .

D. Calcaterra et al. / J. Cult. Heritage 1 (2000) 415–427 421

Figure 4. SEM micrograph of feldspar crystals growingon the residual glassy matrix.

different development and was almost completed inthe Soccavo facies. A subordinate amount of so-dalite and magnetite were also recognized.

5.2. Physico–mechanical parameters

Table III summarizes the physical and mechanicalparameters determined on the Piperno samples fromSoccavo and Pianura.

A comparison between data of the two samplingareas demonstrates a number of relevant differences.First of all, the Piperno sampled at Pianura gave amore homogeneous response to almost every test,compared to the Soccavo material. Pycnometer testsconfirm this statement, since dry densities vary inthe 13–17 kN/m3 range for Pianura (figure 5),while they extend from 15 to more than 22 kN/m3

for Soccavo lithotypes. Open porosity follows asimilar trend (figure 6) while specific gravity remainswithin a very narrow range (24.97–26.26 KN/m3)for both sampling areas (figure 6).

Despite very similar average values of capillarityabsorption coefficient for Soccavo and Pianura(0.027 and 0.03 g/cm2·s1/2, respectively — tableIII), the ranges are substantially different, the Soc-cavo one being much wider (0.0063–0.0434). Liter-ature data concerning similar rocks (volcanic tuff)[37] are very consistent with the reported data, atleast as regards mean values (0.047).

As far as water absorption by total immersion isconcerned (figure 7 and table III), both sets ofsamples display a wide range of variability (11.6–18.2 % and 21.7–27.8 % for Soccavo and Pianura,respectively), even though Soccavo exhibits the low-est values. The order of magnitude for this parame-ter is in good agreement with the scanty dataavailable in the literature on volcanic rocks [37].

The data set on water vapour permeability (tableIII) does not seem to be very dependent on thesampling location. Again, Soccavo samples show awider range.

The greatest differences between Soccavo and Pia-nura facies were recorded on UCS and PLS data.This feature is very evident in figure 8, which re-ports the uniaxial compressive strength related to

cement which reduces the available pore space. Theproducts of vapour phase crystallization in Pipernoare alkali feldspars with a narrow range in chemicalcomposition (Or53–34). They are observed in fiammeas well as in the matrix and their composition isdistinguishable from the few phenocrysts present inthe rock (Or68–43). The minerogenetic process seemsto be confirmed by many gas-escape pipes present inthe upper breccia (e.g. at Verdolino); these verticalchannels testify to the wide degassing of the under-lying Piperno unit [6].

Electron microscopy observations (SEM) confi-rmed the above considerations and demonstratedthe presence of feldspar crystals, with a typicaltabular shape, growing on the glassy matrix (figure4).

Table II reports the results of a mineralogicalquantitative evaluation carried out on a representa-tive sample of Piperno from Pianura and Soccavo.This test showed that, in the Pianura sample, afraction of unreacted glass is still present (about5.5 %), whereas in the Soccavo sample no residualglass was found out. It is therefore supposed thatthe post-depositional minerogenetic process, whichled to crystallization of alkali feldspars, followed a

Table II. Mineralogical quantitative evaluation of representative samples of Piperno from Pianura and Soccavo (tr.=traces)

Total feldspars Sodalite Magnetite AmorphousBiotite Amphibole

0.80.53.595.4Pianura tr.–89.3 3.9 1.5 tr. –Soccavo 5.4

D. Calcaterra et al. / J. Cult. Heritage 1 (2000) 415–427422

dry density. Pianura samples cluster in a very nar-row area, whereas Soccavo samples are scatteredover a wide portion of the diagram, thus confirmingthe high variability of the latter. On this basis,Pianura UCS values (4.7–8.5 MPa) testify to a‘weak and moderately weak’ rock [38]. On theother hand, Piperno from Soccavo exhibits valuesranging between 13.5 and 67.5 MPa, hence fallingin the ‘moderately strong with some strong’ band[38].

Similar considerations can be drawn from PLStests (table III and figure 9). Once again, as far asdata clustering and strengths are concerned, theSoccavo samples proved to be much more scatteredand resistant, compared to Pianura.

As far as ultrasonic measures are concerned, bothdry and wet velocities did not reveal significantdifferences between the two provenance areas. But,if we consider the increase from dry to wet veloc-ities, Soccavo again exhibits a range (6.4–23.4 %)wider than that of Pianura (2.9–13.3 %).

6. Conclusions

After several centuries of exploitation and usagein the architecture of the ancient centre of Naples,Piperno has been thoroughly studied here from dif-ferent points of view, namely mineralogy, petrogra-phy and engineering geology.

Mineralogical and petrographical studies did notreveal significant differences between the two sam-pling locations. However, intense post-depositionalminerogenetic processes were confirmed by thequantitative mineralogical analysis carried out onsome representative samples that exhibited a veryhigh alkali feldspar content and, for the Pianurasample only, a residual 5 % of glass.

On the contrary, as far as the physical and me-chanical features are concerned, almost all testsdemonstrated a marked difference between Pianuraand Soccavo as well as widely ranging data.

Piperno from Soccavo showed the best perfor-mances in terms of mechanical strength, as confi-rmed by the UCS and PLS tests (up to about 70MPa for UCS and 7 MPa for PLS) and partly by theultrasonic velocities. As a consequence, the range ofvalues allows this facies to be defined as a moder-ately strong rock. On the other hand, Pianura faciesfalls completely within the range of weak rocks.

The most striking feature among the physicalproperties seems to be the total open porosity,which is significantly lower for Soccavo (12–40 %)with respect to Pianura (34–50 %). As expected, aT

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D. Calcaterra et al. / J. Cult. Heritage 1 (2000) 415–427 423

Figure 5. Ranges of dry density values within the Soccavo and Pianura sets of samples.

Figure 6. Total open porosity versus specific gravity. Standing two separate fields, Soccavo is more scattered.

direct relationship was found between this parame-ter and water permeability and absorption.

A further difference between the two facies isgiven by the wider data range, constantly recorded

for every parameter measured on the Soccavomaterial.

A tentative explanation of this difference, both interms of absolute values and data range, is based on

D. Calcaterra et al. / J. Cult. Heritage 1 (2000) 415–427424

the heterogeneity of the rock, probably influencedby the relative abundance of the two main compo-nents of the rock: matrix and fiamme. As a conse-quence, it is difficult to consider Piperno as a uniquematerial; the existence of several different horizonscited from the historical literature is most likelyconfirmed.

In view of a better comprehension of the observeddifferences, the wide scattering of the Soccavo data(figure 6, 8 and 9) led to a closer examination of themacroscopic features of this material. This studymade it possible to distinguish at least three lithofa-cies characterized by a different matrix (light grey,dark grey and reddish), the latter including a greater

Figure 7. Water absorption by total immersion as a function of time.

Figure 8. Uniaxial compressive strength versus dry density. Pianura samples cluster in a narrow area. The wide area ofSoccavo samples testify to the high variability of both parameters.

D. Calcaterra et al. / J. Cult. Heritage 1 (2000) 415–427 425

Figure 9. Frequency distribution of point load strength. Pianura samples, showing a good homogeneity, display lowervalues.

amount of fiamme. On this basis, some determina-tions, and in particular capillarity absorption tests,were reconsidered as shown in figure 10. The lithofa-cies macroscopically recognized, exhibited a verydifferent behaviour towards this parameter and onlythe light grey facies seems to be comparable to the

Piperno from Pianura. This feature promoted a furtherinvestigation of this rock in order to define a completecharacterization, starting from a detailed stratigraphiclogging of Piperno, at present not available.

This paper clearly indicates that the mineralogicaland physical characterization of Piperno still requires

Figure 10. Water absorption by capillarity as a function of time for the different facies of Piperno.

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further specific knowledge on the different layersexploited in historical ages. The analysis of an ade-quate number of samples collected in these facieswill provide the tools to interpret the behaviour ofthis rock used as a building stone. This first ap-proach most probably foresees a relationship be-tween the mineralogical composition, in terms of theauthigenic feldspatization process, and the otherinvestigated properties. The collected data, however,do not totally support this first hypothesis.

The different weathering typologies shown in aprevious work [2] seem to be related not only toparticular microenvironment conditions but, aboveall, to the different features of the material used.

The results of this research demonstrated how thisproblem has been disregarded up till now. Thissituation is also confirmed by the total forsaking ofthe exploitation areas which would deserve moreattention as a result of the uniqueness and thelimited extension of the deposit. In fact, the sameattention addressed to historical monuments shouldalso be devoted to the exploitation area that pro-vides the stones used for the monument itself andshould be considered as a cultural heritage by thesame standard. The current unavailability of thisstone makes this necessity more urgent in cases ofrestoration.

Acknowledgements. The research was carried outwith the financial support of the Italian NationalCouncil of Research (C.N.R.) Progetto Finalizzato‘Beni Culturali’, contr. No. 97.00630.PF36 grantedto Maurizio de’Gennaro. Thanks are due to Mar-cello Serracino (CNR, Rome) for his skills in mi-croprobe analyses and to Antonio Canzanella(Federico II University, Naples) for his help in SEMobservations. A final thanks to Maurizio de’Gen-naro and Carlo Manganelli (CNR, Florence) fortheir helpful discussions and suggestions.

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