The Materials of Construction of the West Wall of the Mosque of Cordoba (Spain) and Their Deterioration

THE MATERIALS OF CONSTRUCTION OF THE WEST WALL OF THE MOSQUE OF CORDOBA (SPAIN) AND THEIR DETERIORATION.

MONTEALEGRE,L., Dpto.C.R.Agricolas y Forestales. E.T.S.l.A. Univ. Cordoba (Spain) BARRIOS,J. Dpto. Quimica lnorganica. Facultad de Ciencias.Univ.C6rdoba NIETO,M. Museo Diocesano. C6rdoba (Spain).

KEY WORDS:Upper Miocene, Guadalquivir Basin, Cordoba, Mosque, Biocalcarenite, Stone, Ashlar, Quarry.

SUMMARY The Great Mosque of Cordoba(Spain) is the most important religious monument of the arabic spanish period. It is one of the largest sacred structures of the word. It can be considered as the" Western Mecca". This monument was built in the most brilliant period of cordobesian Caliphate. Add-ar-Rahman I began to built this Mosque in 784 a.C. and it was finish about 976 a.C. This building has a complex architectonic structure due not only to the long period needed for its completion and subsequent restoration processes, but also because of the large number of different material involved in the construction. In this communication we study the material used in the construction of the west wall (wall ang gates) of Mosque of Cordoba (Spain). The building material of the west wall is characterized and mapped. A cartographic study is also made of the different types of alterations observed with the aim of tinting the factors responsible of such effects. The whole building is constructed by calcaires materials (biocalcarenites of Upper Miocene): biomicrites, conglomeratic biomicrites, clay- and sandy-biomicrites, biorudites, biosparites. They are other materials such as: marbles, bricks, stuccos (ornamentation).

This communication can be summerized as follow: 1. Characterization the materials used and identification of possible origin quarries. 2. Mapped of restaurations and performed at different periods and with different materials. 3. Litological mapping. 4. Cartographic study of the different alteration processes. This paper is included as a part of a more complete work about stony materials.

1. INTRODUCTION The Islamic section of Cordoba's Mosque-Cathedral is, without doubt, the starting point for Spanish/Moorish architecture in the Iberian Peninsula. It has been said that this is the oldest building still standing and still in use in Spain. Its peculiar history alone - from great Moorish mosque to diocesan cathedral - makes it one of the most outstanding buildings in the world. As far back as the 15th century it was considered one of the Wonders of the World and was finally declared World Patrimony in 1984. The Mosque has the appearance of a fortress. The enclosure of the site consists of a strong wall of ashlars placed in an outbond/ inbond formation, and crowned with battlement cresting (Fig.1). Several doors open onto this enclosure, one of the most important being " the door of St Stephen" (given this name after the Reconquest) (BARRIOS 1994). The first inscriptions made by muslim artists can been seen engraved on this door. Investigation began on a section of the monument, thus allowing the study of mineralogical and structural characteristics of the different lithotypes found and lithological mapping (FITZNER 1992). 52

Once the rocky materials present had been studied, the search for possible quarries of origin began as their whereabouts were not known. Several quarries near the city of Cordoba (Fig.2) were studied and their particular material content was compared with that of the "ashlars" or stones in the Mosque. The ashlars in the monument had similar characteristics to material originating from rocky formations of "edge facies" from the marine Tortonian in the Guadalquivir Depression ( Fig.3) (MONTEALEGRE 1976, 1990; ESBERT 1988; RODRIGUEZ-NAVARRO 1994). The facies consisted of mixed, arenaceous ( yellowish ) carbonated deposits, rich in fossils and some resedemented microfauna. Their lithology was not uniform and their profiles were not always constant from one to another. The lowest levels were bioconglomeratic. There were 4 stratigraphic sections representing the lithostructural or petrological groups characteristic of this type of formation: biosparites, sandy-biomicrites ( the majority are biomicrites ), calcareous arenites and conglomeratic calcareous biorrudites (MONTEALEGRE 1990 ). Biorrudites and conglomeratic calcareous with quartzite edges are found in abundance in the bed of the formation, as well as volcanic rocks from the Paleozoic era of Sierra Morena. The overlaying bed consists of sandy beds with clays, in the Al-Andalousian transition, capped by thick clayey sedimentation which marks the end of the Miocene.

2. HISTORY Abd-al-Rahaman I ( the first independent emir of Al-Andalus ) ordered construction of the Aljama Mosque to commence at the beginning of Rabi I of the year 170 of the Hegira, the year 786 AD. according to the Christian calender. Construction can be divided into two main historical phases : the Moorish phase, from its construction in the 8th century to the year 1236; and the Christian phase, from 1236 up to modem times. Of the original Mosque, only the doors of the west side survive. The La Leche door dates from the 10th Century and was the centre of restoration work in the 15th and 20th Centuries. There is a gothic allonge dating from the (1475) 15th Century which is being restored (1935) using a mixture of cement and coloured calcareous mortar (thus imitating the ashlars)(Photo 1). As regards the Deanes door, the wall and door date from the 8th Century. The ly~flower decoration on the top the wall is dated in the 15th Century and replaced the old decoration. The aboutement (Fig.4b) is original but it is very modified by replacement of bricks and ashlars. Also in 16th Century,the aboutments were added to the original wall (Figs.1 and 4a). A conglomeratic material was used to substitute some original ashlars in 16th Century.

3. CONSTRUCTION BED-STONES IN THE MOSQUE The rocks most frequently used (Barrios 1994) for ashlars in the west wing of the Mosque were: - Biomicrite ( yellow 2.5 Y )(Photo 2a) and detritical material. These are porous, permeable and of relative macroscopic homogeneity. They contain a high proportion of fossils and limestone-bearing cement, as well as detrital segments of quartz. Microfossils tended to be fragmented. Other minerals present were: feldspar, glauconite, muscovite and some clay. In certain thicker yellow-coloured ashlars iron was clearly visible in thin layers (needle ironstone). This colouration was only present in altered ashlars. - Biosparites (pale ochre and pale yellow, 7.5 YR to 2 Y)(Photo 2b). These rocks were fairly compact, consisted of approximately 20 % spathic cement ( with visible crystallites }, more cristallized than the biomicrites and contained many fossils. The minerals present were: quartz (from 100 to 150m), calcite (at 160m). orthoclase, chalcedony, iron oxides and hidroxides ( needle ironstone, hematite ). The rock fragments ( with diameters ranging from 200 to 300m ) were: quartzites and metamorphical slate-clay from the Precambrian era, volcanic rocks, etc, all from the hercynian massif of Sierra Morena. - Conglomeratic Biomicrites and biorrudites (reddish or yellow-brown)(Photo 2c). These were compact, porous and permeable. Their lithology was similar to that of the biomicrites, consisting of 12 to 10 % reddish conglomeratic fragments, ( .tE > 2 mm). The conglomeratic fragments consisted of: Bunt 53 quartzites, red and green limolites (Bunt and Paleozoic), green and purple volcanic rock (Keratophyre from the Cambrian era ), etc. - Clay biomicrites and bioarenites (yelow 2.5 Y)(Photo 2d). The particle size is less in these two types of rock than in the micrites, and contained a higher percentage of clay and detritical sandy fractions. The bioarenites contained approximately 25 % quartz and a low percentage of clay. They consequently tended to be more altered than the biomicrites mentioned in the first group. Microfauna observed in thin film differed depending on the lithological type. In the biosparites, heterosteginas, lime algae, (lithothanium) , etc, as well as bivalve fragments, brachiopocls, ericius (plates or needles and silk fibres), bryozoans, etc. In biomicrites and clay biomicrites, there were greater quantities of fragments of resedimented and broken foraminifers (heterosteginas, dentallium, etc,) bivalves (ostreas, pectem), ericius (plates and needles), brachiopods, etc. In conglomeratic material, microfauna was usually less common, with the exception of dentalium, heterosteginas, lithothanmium algae, etc. Macrofauna also tended to be well preserved in the ashlars and quarries. Bivalves were observed (ostreas, pectem), brachiopods (terebratullas), ericius (clypeaster), etc. There are many varied "burrow" structures in the ashlars or stones, the most important being Trypanites ichnofacies ( tubes of O filled with sipunculids, polichaetes, bivalves, sponges and others ) and G/ossifungites ( "burrow" pholadides, tha/assinoides, and traces), etc.

4. MAPPINGS. The lithological mapping of the area studied is shown in Figs. 4a, 4b (the La Leche Door and Deanes Door) and 4c (the wafO. The types of alteration (TERREROS 1992) in these doors and panels in the west wing of the mosque have previously been the subject of study (BARRIOS 1994). These are: arenisation, bioalteration and general collapse of structure, crust and to a lesser degree, alveolization, differential alteration, etc, .

5. THE STONE QUARRIES The location of the quarries of origin is not known, but based on litholgy and structure, they most probably belong to the " edge facies" formation of the marine Tortonian of the Guadalquivir Basin. In the aforementioned lithological formation, there is no single pattern governing the sequence, thickness and properties of materials which may be applied to the alignment of the ridge as a whole. This becomes more apparent when compared with other quarries in the area (Las Cuevas, Naranjo, Patriarca, etc). The sedimentary sequences of some of the outcrops where the stone quarries are located are shown from west to east in Fig.2, as well as the stratigraphy of each quarry. The heterogeneity, both in lithology as well as in the relative succession of occurrence was also noted. The characteristics of the rocky formation suffer constant changes from section to section, even within the same quarry. The present study concentrates on 3 of the existing quarries. POSADAS (N°1 , Fig.2) This is one of the most important deposits due to the area it covers and the volume of rock extracted. Thin detritical surfaces are more common, fair1y compact and relatively homogenous laterally, but in only a few metres the mechanical properties may suddenly vary and this is not easily observed.(Photo 3a) LA ALBAIDA (N°2, Fig.2) Outcrops of the lowest section of the formation, including the sole (wall) were observed here. There are greater quantities of conglomeratic deposits, together with sandy biocalcarenites and biomicrites. The deposit is one of the closest to the city and one of the most important as regards the thickness of the rocky formation and the area of the different digging surfaces, some of which contain extractive morphology from the last century (Photo 3b). ASLAND (N° 5, Fig.2) In this quarry, the carbon and clay content varies frequently and levels of blue arenite containing lime-algae were common, especially in the sole. There were thin and highly compact layers located near the over1aying bed of the formation which correspond to periods of greater faunistic content in chalk water.(Photo 3c) 54

6. COMPARATIVE STUDY

Mineralogical data obtained by optical microscopy ( thin section ) and Diffraction of X rays are presented as percentages in Table I. Data from the 3 quarries studied is shown (Q- Albaida, Q- Asland and Q-Posadas) as well as the four most common rocks in the ashlars (M- bioarenite, M-conglomeratic, M-biomicrite, M biosparite ) . The most relevant petrostructural characteristics have been studied and data obtained has been presented as percentages in Table II. The percentages of silica consist of: quartz, opal, feldspar, etc. The percentages of carbon include: matrix, cement, calcareous fossils, calcite, ankerite, etc. The percentage of fossils present is included in the total carbonates. The porous values correspond to visible spaces. The data obtained reveals the changing composition which exists between some levels and others within the same layer or section of the "edge facies" formation. It should be noted that rocks or fragments of rock with a diameter greater than 4mm and which tend to be found exclusively in conglomeratic levels have not been included. Quartz is present in varying sizes (sand and gravel fragments). There are occasionally other materials which we have not included in the tables, and which consisted of general rock fragments: red quartz, some fragments of red volcanic rock, arenite and Paleozoic quartzite, anphibolite, andesite, marble, Cambrian limestone, and other rocks which were unidentifiable due to their high degree of alteration. Among the carbonates, apart from calcite, which is dominant, ankerite, dolomite and, occasionally, aragonite were observed. Feldspar was not common and orthclase and plagioclase were observed, the latter only being clearly visible in highly altered ashlars, or material affected by its proximity to iron. Other minerals included: mica ( muscovite), clayey minerals ( glauconite, illite, smectite, chlorite, etc.) In Table 111, the data corresponding to chemical composition is presented as percentages of oxide. Quartz is included in silica, and calcite in the value C03R (R indicates Ca fundamentally). The presence of Al, Fe ( in part ), K, Mg ( in part ) represents the presence of feldspar and/or micaceous or clayey minerals, together with a small quantity of silica. The occasional presence of S may indicate sulphates ( gypsum ). P.F. indicates loss on ignition.

7. OTHER DATA The mechanical characteristics (compression tests in perpendicular and in parallel), ultrasonic speeds and hydric properties are studied in both the ashlars as well as the materials in the quarries. Some of the results obtained are summarized in Table IV.

BIBLIOGRAPHY.

BARRIOS-NEIRA,J., NAVAS,J., MONTEALEGRE, L. and NIETO,M. (1994) II Characteristics and types of alteration in materials found in the west fa<;ade o9fthe Mosque of C6rdoba (Spain)". Proc. Ill Inter. Symp. on the conservation of Monuments in the Mediterranean Basin. 755-761 .Venecia (Italia) BARRIOS-NEIRA, J., MONTEALEGRE, L. and NIETO, M. (1996) " El Alcazar de los Reyes Cristianos de C6rdoba: materiales petreos y canteras". Proc. 111 Congr. Inter. de Rehabilitaci6n del Patrimonio Arquitect6nico y Edificaci6n. 238-242. Granada (Espana). FITZNER, 8 ., HEINRICH, Kand KOWNATZKI, R. (1992)" Classification and mapping of weathering forms". Proc. 7th Inter. Congr. on Deterioration and Conservation of Stone. 957-968. Lisboa (Portugal). ESBERT, R.M., ORDAZ, J. and ALONSO, F.J. (1988) " Caracterizaci6n petroffsica y alterabilidad de las piedras de la Catedral de Sevilla." Materiales de Construci6n, 30, 5-23. Madrid (Espana). MONTEALEGRE, L. (1976) "Estudio mineral6gico de sedimentos y suelos en la Oepresi6n del Guadalquivir". Tesis doctoral, Universidad de Granada, 672 pp. MONTEALEGRE, L. (1 990) "Geologfa de la Depresion del Guadalquivir". Jomadas de Geog. Ffs.y Analisis ambiental. 61-78. Cordoba (Spain). 55

RODRIGUEZ-NAVARRO, C., SEBASTIAN PARDO, E. and ZEllA, U. (1994) Petrophysical-Mechanical parameters for decay evaluation of building stones. A case study: Jaen Cathedral (Andalousia, Spain). Proc. Ill Inter. Symp. on the Conservation of Monuments in the Mediterranean Basin. 595-004. Venecia (Italia). TERREROS G.G. and ALCALDE M. (1992)" Factors and indicators of stone deterioration at the principal portal of the School-Seminary of San Telmo in Seville." Proc. 7th lnter.Congr. on Deterioration and Conservation of Stone. 1001- 1009. Lisboa (Portugal).

Table I: Mineralogy ( % )

sample % quarz % calcite %ankerite %feldspar % micas % others

Q-Albai. 23- 28 40-55 0-3 7-12 4-8 2-6

Q-Asland 5-15 65-80 2-4 2-5 2-7 2-4

Q-Posad. 10-15 70-82 2 3-5 2 0

M-baren. 20-35 25-55 2-4 2-8 3-15 2-5

M-congl. 20-30 35-60 3-8 5-10 3-10 5-10

M-bmicr. 5-12 60-70 3-7 1-4 2-5 2-5

M-bspar. <10 80-85 1 <5 <5 2 Q =quarry, M = Mosque. bioarenite, conglomeratic, biomicrite, biosparite.

Table ll:Characteristics petrostructurals (%)

sample % carbonates % silica % porosity % fossils

Q-Albaida <60 25-30 <15 40-50

Q-Asland 70-80 7-17 10-15 20-30

Q-Posadas 75-85 10-12 8-13 25

M-bioaren. 65 20 12 20

M-conglom. 60 25 15 15

M-biomicr. 80 10 10 32

M-biospar. 80-85 <10 <10 40 56

Table Ill: Chemical Composition (%)

sample Si02 cao AbOJ F!!:!OJ t

0-Alb. 22,85 35 5,06 2,11 1, 16 1,04 0,05 1,7 61,5 31

Q-Asl. 11 ,08 47,45 1,31 0,94 0,49 0,38 0 0,53 85,25 31,81

0-Pos. 13,47 44,9 2,65 1,04 0,63 0,43 0 0,8 80,75 38

M-baren 22,25 37,39 3,13 2,83 1 1 0,1 1,3 67 31,12

M-congl 28,96 34,79 3,35 1,59 0,77 0,56 0 1,36 62,87 28,62

M-bmicr 11,41 45,11 3,2 1,53 0,55 0,63 0 1,42 80,5 36,13

M-bspar 6,21 50,59 1 0,75 0,2 0,43 0 0,48 91 40,34

Q-Albaida., Q-Asland, Q-Posadas. M-bioarenites, M-conglomeratics, M-biomicrites, M-biosparite.

Table IV: Others data

2 Sample Comprenssion resistance (kg/cm ) Ultrasonic speed (km/s)

Biosparite 290 250 3.2 2.8 Biomicrite 190 130 3 2.8 Bioarenite (altered) 60 50 3.5 3.6 POSADAS 130 105 2.7 3.1 57

Original ashlars Bricks 18th Century Ashlars 20th Century (second half)

Ashlars 15th Century Resins 20th Century (second half)

Ashlars 16th Century

Fig.1 . Historic mapping of the walls

Biorrudite ~~ :~ Conglomerates Ii : :1 [2 m Bioesparite . Bloarenite + ~ E8 Sandy-biomicrlte D . Blomlcrite ~ Clay Blomlcrlte ~ Bioesparrudlte ~ Sandy blc>e$1>4rite 5

2 6 4

. ' ... mI I

Albalda Patrlarca Naranjo Posadas

FIGURE 2. SERIES AND UTOSTRATIGRAPHYC CORRELATION.

Fig.2 Series and lithostratigraphic correlation 60

LEGE HO Quarrier abanclollM or ..._._ (deer...... ,.,,_,

clly''"., I •lllage "faclee °' borcle" lounatk>n ,...-(P'alNozolo I Trlaa)

~5Km

Fig.3 . Cartography of" Borde Formation" Guadalquivir Basin

a ' b

Conglomeratic Biorrudile

Biomicrite Biosparite

Clay biomicrile Old brick

Resins Recent brick

. .. Painting Coatings

C '

Fig.4 . Lithological mapping : a) La Leche door ; b) walls and c) The Deanes door