A methodology for locating the original quarries used for constructing historical buildings: application to Málaga Cathedral, Spain

Engineering Geology 54 (1999) 287–298

A methodology for locating the original quarries used for constructing historical buildings: application to Ma´laga Cathedral, Spain E. Gala´n a, *, M.I. Carretero a, E. Mayoral b a Departamento de Cristalografı´a y Mineralogı´a, Facultad de Quı´mica, Universidad de Sevilla, Prof. Garcı´a Gonza´lez s/n, Apdo. 553, 41071 Sevilla, Spain b Departamento de Geologı´a, Facultad de Ciencias Experimentales, Universidad de Huelva, 21819 Palos de la Frontera, Huelva, Spain Received 3 August 1998; accepted for publication 3 February 1999

Abstract It is often necessary to locate the original quarry which supplied the stone for a particular historical building. This stones could be used for future restoration work and for testing in the laboratory (artificial aging tests, physical properties determination, control of the efficacy of conservation treatments, etc.). Generally, reviewing historical documentation gives information about the geographical setting of quarries and location of the stones in the monument, but this information needs to be proved by field and laboratory studies. The comparative study of stone from quarries and monuments should basically include the following: (1) mineralogical and petrographical studies; (2) the chemical analysis of major, minor and trace elements; (3)stable isotopes determinations; (4) physical properties of quarry materials and unweathered building stone (water absorption, ultrasound transmission velocity, porosity and porous system, density, bulk density, compressive strength, etc.). This methodology was applied to Ma´laga Cathedral stones represented in the main fac¸ade, towers, and the western zone of the terrace, which, according to historical literature, came from Almayate (Miocene–Pliocene limestones) and Cerro Coronado (Permotriassic sandstone) in Ma´laga. The conclusion of the comparative study carried out on quarries and building stones was consistent with the information available from the historical documentation. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Limestone; Ma´laga Cathedral; Methodology; Quarries location; Sandstone

1. Introduction In studying the cause and mechanisms of the alteration of monument stone and/or the possible conservation products which can be applied as support or to avoid deterioration, it is sometimes necessary to have at one’s disposition, a stone with similar characteristics to that used in the building * Corresponding author. Tel: +34-5-4557140; fax: +34-5-4557141. E-mail address: [email protected] (E. Gala´n)

in order to carry out laboratory studies (tests of accelerated alteration which simulate the environmental conditions of the edifice, variation of the physical properties with the alteration, testing of the efficiency of treatments for conservation, etc.) and also with the aim of possible restoration work which would involve replacement of badly damaged zones (Guerrero et al., 1988; Fitzner and Kalde, 1991; Alonso et al., 1994; Gala´n and Carretero, 1994; Carretero and Gala´n, 1996; Wessman, 1996). The ideal situation would be to use stone from

0013-7952/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S0 0 1 3 -7 9 5 2 ( 9 9 ) 0 0 04 2 - 3

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the quarries which supplied the original stone used, but failing this, if this stone is not accessible or the quarries no longer exist it is necessary to use stones from other quarries with similar properties to the originals used. In any case a comparative study should be made of the stones from the quarry and from the monument in order to establish any similarities. Various methods have been proposed for identifying the quarries which supplied the original stone used in the construction of monuments. These methods are based on the analysis of trace elements and rare-earth elements, the determination of stable isotopes, cathodeluminescence analysis, etc. (Herz and Dean, 1986; Herz, 1987; Decrouez et al., 1988; Barbin et al., 1992; Bello et al., 1992; Gaspari et al., 1992). In this work we propose a methodology for the identification of the original quarries which supplied the stone used in the monuments, which was applied to the stones of the principal fac¸ade, the towers and the western zone of the terrace of Ma´laga Cathedral (southern Spain).

2. Work methodology proposed for identifying original quarries used to supply the stone used in monument construction To locate the original quarries used to supply stone for an historic edifice, we propose the following scheme of work (Fig. 1): 2.1. Examination of the historic documentation The study of the historic documentation of a monument allows us to obtain information on the location of the original quarries and the location in the monument of stone which has been extracted from those quarries. Therefore, it is convenient to examine the historic documentation of the monument (city and monument archives, publications on the edifice, etc.) with special emphasis on the details of materials used and their origin, the various construction steps including the quarries used for each step, the location of the stone in the edifice, etc. It is also important to take into account any

restoration which has been carried out and, in the cases where replacement of stone has taken place, the origin of the stone used. 2.2. Geological study Previous sampling has shown that it is essential to make an exhaustive local and regional geological study, because when stone used in the building has come from a currently non-accessible quarry or when there is no accredited documentation about the quarry used, it is necessary to search for other quarries with the same geological formation. 2.3. Sampling from quarries and buildings The next step in this investigation is to obtain a series of samples in the quarries originally used in the construction of the monument, supposing that these are still accessible, and also samples from any zones of the edifice where historic studies indicate what stone from which quarry was used. The sampling in the edifice must be carried out, for each litotype, on the least altered stone, since the mineralogical, chemical and physical characteristics of a rock vary with the degree of alteration (Gala´n, 1990; Hammecker and Jeannette, 1988). If the quarries utilized in the original construction are not accessible (due to construction of urban zones, exhaustion of the stones, etc.) samples can be taken from other quarries with the same geological formation and can be checked to see if their petrographic characteristics and properties are similar to the stone used in the monument. 2.4. Stone characterization The following studies must be carried out on the samples from the monument and from the quarries: 1. Mineralogical and petrographic analysis by X-ray diffraction ( XRD), polarizing microscopy, scanning electron microscopy (SEM ); etc. 2. Chemical analysis of the major, minor and trace elements by atomic absorption spectrometry (AAS ), inductively coupled plasma-mass spec-

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Fig. 1. Scheme of work methodology.

trometry (ICP-MS ), ultraviolet–visible ( UV– Vis) spectrophotometry, volumetry, etc. 3. Determination of stable isotopes (mass spectrometry). 4. Determination of the physical properties: porosity and porous system, density, bulk density, velocity of ultrasound transmission, capacity of

water absorption, resistance to compression, etc., following the testing standards available (such as RILEM, NORMAL, ASTM, ISRM, etc.). In particular, special attention should be paid to a study of the porous system, using a combination of Hg-porosimetry, N adsorption (BET ) and 2

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Fig. 2. Geologic setting of the sandstone and limestone quarries.

digital image analysis applied to microscopic observations for determining pore size volume and distribution. In general, the techniques used will take into account the laboratory facilities available. Some of the physical properties cited can also be determined in the edifice using non-destructive techniques (absorption of water using a Karsten tube, impact resistance with a Schmidt hammer, etc.) or otherwise using techniques which require a very small quantity of the sample (e.g. pointload test). In the quarries any determinations must be carried out using the same techniques which were used in the edifice so as to obtain comparable results.

study can be carried out. This will indicate the degree of similarity between the stone of the quarries sampled and that belonging to the edifice. It might be helpful when tackling a comparative study to make a statistical analysis of the data obtained from both the quarries and monument samples: mean; standard deviation; correlation coefficients; principal components analysis (PCA); and hierarchical ascending classification, etc. Using the results of this study it is then possible to determine which quarries were used in the construction and the areas of the edifice where those stones are situated.

2.5. Comparative study of the results

3. Application of the working-plan proposed for Ma´laga Cathedral

Once the stones of the monument and the quarries have been characterized a comparative

An examination of the existing documentation on the construction of Ma´laga cathedral in the

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archives and records of the cathedral, as well as of more recent publications on work on the cathedral, show that there were two main stages of construction ( Torres Balba´s, 1960; Isla Mingorance, 1977; Pe´rez del Campo, 1985; Llorden, 1988). During the first stage (1528– 1588), the eastern section of the cathedral was constructed using stone from quarries very close to the city. During the second main stage of construction (1721–1782) the main fac¸ade and the towers were constructed, and the north and south sides were united. The quarries used in the first construction phase of the cathedral are no longer accessible because they are situated in urban areas, consequently this study focused on zones which were constructed during the second stage, and the structural stones for which, according to the historic documentation, came from quarries situated in the region of Cerro Coronado, 2 km NNW of the centre of the city (used in the construction of the first and second bodies of the principal fac¸ade and towers), and from the quarries at Almayate, ca 25 km to the east of the city (used in the construction of the

third and fourth bodies of the north tower, and the western part of the terrace). At the Cerro Coronado quarries Permotriassic red sandstone from the Malaguide Complex was mined (Azema, 1961). The Almayate quarries supply post-orogenic tertiary yellowish limestone from the marine Miocene–Pliocene of the Betic Cordilleras (Mayoral & Rodrı´guez, 1994) ( Fig. 2). The samples taken for this study belong to two well defined lithotypes: red sandstone from Cerro Coronado and yellow bioclastic limestone from Almayate. The sampling in the cathedral was carried out considering different orientations and different levels, taking 10 samples of limestone and 14 of sandstone. In the quarries a total of 15 samples were taken, nine of limestone and six of sandstone. For the stone characterization the following determinations were carried out: 3.1. Petrographic characterization Petrographic characterization was done using a microscope Nikon Optiphot pol.

Table 1 Petrographic, mineralogical, chemical and isotopic data of sandstones and limestones from quarries and buildings

Sandstones

Limestones

Group

Petrographic characterization

Mineralogy

Mineralogy of <2 m fraction

Chemical analysis

Stable isotopes

Cathedral

A

Orthoquartzites of siliceous cement

>90% Quartz No dolomite

Illite, kaolinite, illite–smectite interstratified

–

Cathedral and quarries

B

Protoquartzites and subarkoses. Carbonate cement

70–90% Quartz 5–25% Dolomite

Cathedral and quarries

I

Bioclastic limestones

≥70% Calcite ≤12% Phyllosilicates No dolomite

>94% SiO 2 <0.5% CaO ≤0.1% MgO 2–4% Al O 2 3 0.2–0.4% Fe O 2 3 70–90% SiO 2 2–7% CaO 1–5% MgO 2–4% Al O 2 3 0.5–1.1% Fe O 2 3 >40% CaO 0.3–0.8% MgO <4%Al O 2 3 <0.7% K O 2 0.6–1.1% Fe O 2 3 37–40% CaO

Cathedral

II

60–70% Calcite ≤15% Phyllosilicates 9–11% Dolomite

Illite, kaolinite, smectites, chlorite, illite–smectite interstratified

2–3% MgO ≤4% Al O 2 3 0.3–0.9% K O 2 0.6–1.8% Fe O 2 3

d13C : (PDB) −3.94 to −5.21 d18O : (SMOW) 24.17–25.28 d13C : (PDB) −6.23 to −7.10 d18O : (SMOW) 25.58–26.41

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3.2. Mineralogical analysis

3.5. Physical properties

Mineralogical analysis was carried out by XRD of the total sample (random powder diffractogram) and the <2 mm fraction (diffraction diagram of oriented aggregate). For this we used a Philips diffractometer (model PW 1130/90) using Ni-filtered Ka radiation of Cu, equipped with an automatic slit.

1. Velocity of transmission of ultrasound using a Pundit apparatus. The methods with the quarry stone were carried out in test specimens of 5×5×10 cm. In the cathedral direct and indirect methods were used on the ashlars from which the samples for this study were taken. 2. The porosity was studied by Hg-injection, using a Micromeritics porosimeter model autopore 9220; adsorption of nitrogen (BET ) using a Micromeritics apparatus model ASAP 2000; and by image analysis under a microscope. For the image analysis the sample was impregnated in vacuo with a mixture of resin and fluorescent colouring and a thin section was prepared according to the usual method. The empty spaces under the microscope were a yellow colour with normal light and a light yellow/green fluorescent colour with UV light. Using a camera adapted for use with the microscope, we obtained successive photographs of the thin section (at an average of 30 photographs per sample). These were processed and analysed using an computer and in this way quantitative values were obtained for the distribution of pore size and the total porosity. The real and bulk densities were obtained directly with the Hg-porosimeter. 3. The water absorption capacity was measured using a Karsten tube (pipe method ) (RILEM, 1978). 4. Impact resistance, using a Schimidt hammer, which was used so as to obtain in situ, immediate, non-destructive measures of the mechanical resistance, using a calibration curve which was incorporated into the apparatus. These measures were carried out with a controls type hammer, with a angle of a=0° between the hammer and the stone.

3.3. Chemical analysis Chemical analysis of the major and minor elements (Si, Ca, Mg, Al, K, Na, Fe, S) and the trace elements (Mn, Ni, Co, Cu, Zn, Pb, Sr, Ba, Cr, Cd ) was carried out. The elements Ca, Mg, Al, Fe and the trace elements were determined by atomic absorption spectrometry and Na and K were detected using a Perkin–Elmer spectrophotometer, the sample being previously dissolved by means of a triacid attack. In the samples where the concentration of Ca and Mg was very high, the determination of both these elements was carried out by volumetry. The analysis of Si was carried out by colorimetry in an UV–V spectrophotometer. The sulphates were precipitated with barium acetate and the turbidimetry determined.

3.4. Stable isotopes The stable isotopes of 18O and 13C were determined following a method based on those described by McCrea (1950) and Craig (1957). For this we used an ISOCARBs@ equipment which was connected to a mass spectrometer of type SIRA-II @ ( VG Isotech). For the determination of the isotopes of carbon and oxygen in calcite ( limestones), we analysed the CO produced over 3 h 2 by the sample reacting with phosphoric acid. In the case of dolomite (sandstones), the time of reaction was 3 days. The accuracy of the method was ±0.02‰ for d13C and ±0.12‰ for d18O. As standards references, we used the PDB standard (peedee belemnite) for C, and the SMOW standard (standard mean ocean water) and PDB both for oxygen (O’Neil, 1986).

4. Results and discussion 4.1. Sandstone 4.1.1. Petrographic study A petrographic study classified the sandstone samples into three different groups (Pettijohn, 1975). The group of the orthoquartzites with silica

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cement, formed entirely by building samples, and the groups of protoquartzites and subarkoses (with samples from the cathedral and quarries) which are cemented with a sparitic carbonate, and with iron oxides and clay minerals in certain cases. 4.1.2. The mineralogical and chemical analysis The mineralogical and chemical analysis of the sandstones divided all the samples into two groups ( Table 1, Fig. 3(a)), one consisting of the orthoquartzites (A) (only the cathedral samples), with

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>90% of quartz, and a second group (B) (cathedral and quarry samples) constituted by the protoquartzites and subarkoses, which are composed of quartz, feldspars and dolomite (5–25%). Nevertheless this difference is not deductible from the trace element contents [Fig. 3(b)], as it occurs in other cases (Barbin et al., 1992; Bello et al., 1992). The high values of Zn and Pb in the cathedral samples is probably due to pollution (Crnkovic and Miko, 1991; Cala et al., 1992; Carretero and Gala´n, 1996).

(a)

(b)

Fig. 3. (a) Major and minor elements of building and quarry sandstone samples (average values for each group). (b) Trace elements of building and quarry sandstone samples (average values for each group).

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Table 2 Isotopic values of 13C and 18O from quarries and building sandstones and limestones

Sandstone

Quarry (B) Quarry (B) Cathedral (B) Cathedral (B) Cathedral (B) Quarry (I ) Quarry (I ) Cathedral (I ) Cathedral (I ) Cathedral (I ) Cathedral (II ) Cathedral (II ) Cathedral (II )

Limestone

d13C (PDB)

d18O

−5.21 −3.94 −5.05 −4.21 −4.37 −6.23 −6.55 −6.97 −7.10 −6.98 −6.79 −6.99 −6.66

−5.46 −6.54 −3.77 −6.42 −6.30 −4.36 −4.58 −5.04 −5.16 −4.73 −4.48 −4.81 −4.48

d18O (SMOW)

(PDB)

25.28 24.17 27.03 24.29 24.41 26.41 26.19 25.71 25.58 26.03 26.29 25.95 26.29

Table 3 Physical properties of sandstones and limestones from quarries and building (average values for each group)

Sandstones

Cathedral

Limestones

Quarries Cathedral Quarries

Group

Ultrasound transmission velocity (m s)

Porosity (%vol.)

BET (m2 g−1)

Density (g cm−3)

Bulk density (g cm−3)

Water absorption (ml min−1)

Mechanical resistence (kg cm−2)

A B B I II I

3317 3238 3472 2000 4500 2037

15–17 15–17 13–15 36–39 19–21 34–37

0.63 1.88 3.40 0.52 2.31 2.81

2.64 2.68 2.68 2.70 2.73 2.69

2.25 2.23 2.35 1.56 2.20 1.76

0.04 0.05 0.03 2.56 0.06 2.50

650 640 660 100 380 100

The Mg from sandstones of group B is contained only in dolomite, and as the values of the correlation coefficients of Fe versus Mg (r=0.82) and Mg versus Mn (r=0.98) are positive and high, we may deduce that Fe and Mn are also associated with dolomite. Likewise, the high correlation of Al versus K (r=0.85) indicates that the feldspars are fundamentally potassic. Ba appears positively correlated with K (r=0.74), suggesting that this element is included in the feldspars. We should point out that the cathedral samples have, as a whole, smaller amounts of Ca, Mg, Fe and Mn than those from the quarries possibly due to alterations in the cathedral causing a loss of carbonates and consequently any associated elements. These processes cause an increase in SiO 2 in the cathedral stones [Fig. 3(a)].

4.1.3. Stable isotopes The determination of the stable isotopes was carried out in the samples which had a carbonate cement (only group B) and for this purpose five samples were selected, three from the cathedral and two from the quarries. The data obtained were similar for all the samples studied ( Table 2) showing the similarity between the samples belonging to group B (cathedral and quarry). 4.1.4. Physical properties On the other hand there were no appreciable differences between the values of the physical properties for the sandstones belonging to groups A and B ( Table 3), except in the porous system, since although all the samples have pores of the bottle neck type the entry to these pores had a

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radius of<4 mm for sandstones of group B and >4 mm for those of group A. Concerning the physical properties for the quarry and cathedral samples of group B, the quarry stone values are slightly different in relation to those for the cathedral stone, probably due to the alteration in the cathedral, although we chose apparently fresh samples for this study. It could be thought that the orthoquartzite samples (all these samples are from the cathedral ) were protoquartzites which have lost their dolomitic cement due to various alteration processes. However, in view of the values of the physical properties, this does not seem probable since if there had really been a loss of intergranular cement the values of the physical properties would be very different and under the microscope interparticle porosity due to the cement dissolution would be seen. 4.1.5. Conclusion To conclude, our comparative study suggests that the cathedral sandstone belonging to group B came from quarries in Cerro Coronado and those of group A belong possibly to other Permotriassic sandstone-quarries of the region which have not been taken into consideration in this study. 4.2. Limestone 4.2.1. Petrographic study In the case of the limestone, a petrographic study indicated a great similarity between all the samples. They are sandy bioclastic limestone (Folk, 1962) with a sparitic cement granular and drusic in type, with 20–40% of bioclasts and 15– 25% porosity of geode, channel and intraparticle types. 4.2.2. Mineralogical and chemical studies Mineralogical and chemical studies differentiated between two well-defined types (I and II ) [ Table 1, Fig. 4(a)], the first of which comprises samples from the cathedral and the quarries and the second contains only stone from the cathedral, the two types being basically differentiated by the dolomite content (0.3–0.8% MgO for group I and 2–3% for group II ). With regard to the trace

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elements there were not differences between all the samples [Fig. 4(b)], except for Zn and Pb which could be due to urban contamination, according to various authors (Crnkovic & Miko, 1991; Cala et al., 1992; Carretero & Gala´n, 1996). Taking into account the chemical analyses of all the limestone samples, we deduced that Fe presents a high and positive correlation with Al (r=0.91) and K (r=0.78) and a negative correlation with Ca (r=−0.91) from which one may deduce that Fe in these samples is partially associated with phyllosilicates. Mn has a high and positive correlation with Fe (r=0.74) and a negative correlation with Ca (r=−0.76) from which it may be deduced that Mn forms part of the free oxides together with Fe and none of these is an essential component of the carbonates. Zn, Ni, Cr and Co are partially associated with the phyllosilicates, while Co and Ni are also associated with iron oxide. Finally, Ba is a component of the micas and possibly of the feldspars since it shows good correlation with Al, K, Na and Fe. The alteration processes in these limestones caused quartz and phyllosilicates loss, therefore the concentration of SiO in the cathedral samples 2 is smaller than in the quarry samples [Fig. 4(a)]. 4.2.3. Stable isotopes The determination of the stable isotopes of carbonates in limestones, was carried out in indifferentiate calcite (clast or cement) from two quarry samples and six from the cathedral, three belonging to group I and three belonging to group II. The values obtained ( Table 2) indicated that all the samples were very similar, consequently there was a strong geochemical and genetic similarity between the limestone from the quarries studied and that of the cathedral independently of the mineralogical and chemical groups defined. 4.2.4. Physical properties On the other hand the values of the physical properties ( Table 3) differentiate clearly between groups I and II of the limestone, those of group II being much more compact with less porosity and capillarity coefficient and a larger velocity of

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(a)

(b)

Fig. 4. (a) Major and minor elements of building and quarry limestone samples (average values for each group). (b) Trace elements of building and quarry limestone samples (average values for each group).

transmission of ultrasound, mechanical resistance and bulk density. 4.2.5. Conclusions In summary a comparative study of the results obtained gives rise to the conclusion that the cathedral limestone belongs to two groups, one of them, group I, came from the Almayate quarry while the limestone of group II showed different properties to those of the quarries studied.

5. Conclusions From the comparative study of the petrographical, mineralogical, isotopic, chemical and physical properties of the samples of limestone and sandstone which were chosen from the cathedral and from the quarries of Cerro Coronado and Almayate, one may deduce that the first and second body of the principal fac¸ade and the towers of the cathedral were fundamentally constructed using

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sandstone from the Cerro Coronado quarry, although, there also exists another type of sandstone which from quarries different to those sampled but belonging to the same geological setting. The third and fourth body of the north tower and the western zone of the terrace of this Cathedral was built with limestone from the Almayate quarries but there is also a dolomitic limestone with different properties to that from Almayate. The methodology proposed in this work gives a reasonable identification of the quarries from which the stones of a monument are taken.

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