223

THE PHYSICO-CHEMICAL PROPERTIES OF THE WEATHERED CAPPADOCIAN TUFF AND THEIR SIGNIFICANCE ON CONSERVATION STUDIES

TOPAL, TAMER and DOYURAN, VEDAT

Geological Engineering Department, Middle East Technical University, 06531 , Ankara, Turkey

SUMMARY The tuffs of the Cappadocia region and unique earth pillars, the so-called "fairy chimneys" are undergoing serious deterioration due to atmospheric effects. Conseivation studies require the

determination of the physico-chemical properties of the weathered zones of the tuff and the

understanding of their effects on the engineering behaviour of the tuft. To achieve this task, the physico­chemical properties of the weathered tuff have been investigated through optical microscope, methylene blue adsorption, X-ray diffraction, X-ray fluorescence, and various index tests (dry and saturated unit

weight, effective porosity, water absorption) . The lichen-covered surfaces and discolored zones adjacent to joints are found to be the mostly affected zones. The mechanical weathering is minor and totally

ceases at a depth of 8 to 10 cm, whereas chemical weathering is restricted to the upper 2 cm in the case of lichen-covered surfaces, and 20 cm adjacent to joints. Oxidation of biotites and rock fragments cause discoloration of the tuff. The alteration of volcanic glass and rock fragments produces smectite-type clay

mineral. Macro tension cracks are formed around completely weathered rock fragments. Conservation

studies should consider different swelling strain and associated pressures developed upon wetting of clays; tension crack development around altered rock fragments; and, the oxidation potential of iron

containing materials in contact with water and air.

1. INTRODUCTION

The Cappadocia region of Central Anatolia has long been recognized as an outstanding area due to its

spectacular and unique landforms, and historical heritage. In the region, "fairy chimneys" are formed

within the tuffs by the natural processes of weathering and differential erosion. Typical occurrences of the fairy chimneys may be seen within Orgi.ip, U9hisar, and Avanos triangle, located 10 km east of Nevpehir (Figure 1). Some of the dwelled fairy chimneys were inhabited in the past, and contain valuable

wall paintings inside dating back to Byzantine times. Due to the active natural processes as well as human activities, they are undergoing serious deterioration. Therefore, some spectacular examples and

those containing valuable wall paintings need to be protected. Studies towards conservation have already been started and necessitate the understanding of the processes which cause deterioration of the

tuffs. In this study, physical and chemical weathering products of the Cappadocian tuft are investigated to determine the state and depth of weathering of the tuff, and to predict the engineering behaviour of the

tuft.

2. SITE GEOLOGY

The Cappadocia region is generally underlain by a thick and extensive deposits of volcano-sedimentary

sequence (Miocene-Pliocene) of the Orgi.ip formation (Pasquare, 1968). Although the formation comprises a number of well-distinguished members, in the study area only the Kavak and Tahar

members contain the fairy chimneys. Both members are characterized by non-welded tuffs. Since most

of the dwellings and wall paintings are found within the fairy chimneys of the Kavak member, our study is

focused on this member. The Kavak member represents the product of the first intermittent volcanic activity which produced the

Orgi.ip formation. Thus, this member constitutes the basal portion of the volcano-sedimentary sequence.

The chaotic arrangement of pumice fragments within the unit suggests that it is an ash flow tuff

deposited in a lacustrine environment. It is dirty white to pink, and contains phenocrysts of plagioclase,

224

quartz, biotite and opaque minerals. Various rock fragments and pumice are also commonly observed. In

the matrix, volcanic glass shards are rather common (Topal and Doyuran, 1994; M.E.T.U., 1987). Two

dominant joint sets (N80°E/85°NW and N03°E/90°) are developed within the tuff and they control the

formation of the fairy chimneys (Topal and Doyuran, 1995). In this paper, the term "Cappadocian tuft'' is

used to denote the Kavak member.

5.--\..\CPLE LOC..\TIO~S

0 iron-stained ~le

'-i

I \

)

0 5 IO Km \

. - -·-

Figure 1. Location map of Orgi.ip-Uc;:hisar-Avanos area.

3. PHYSICO-CHEMICAL PROPERTIES OF THE WEATHERED CAPPADOCIAN TUFF

Weathered zones in rocks are formed due to complex physico-chemical processes. Chemical

deterioration affects both chemical and associated mineralogical properties of rocks through their contact with the atmosphere. Physical deterioration, however, produces fractured rock in macro and/or micro

scale (Loughnan, 1969; Carroll, 1970). From alteration point of view, volcanic glass of tuffs is the most

unstable component and decomposes more readily than the other associated mineral phases because it has a poorly ordered internal structure consisting of loosely linked Si04 tetrahedra with considerable

intermolecular space (Fisher and Schmincke, 1984). From physical deterioration point of view, the minerals of tufts especially those having cleavages are fissured .

In order to determine the state and depth of weathering of the Cappadocian tuff, mineralogical and

petrographical , chemical , and physical properties of the weathered zones of the tuff are studied.

Mineralogical and petrographical properties of the weathered tuff are studied by polarizing optical

microscope, methylene blue adsorption test, and X-ray diffraction (XRD). The chemical properties of the

weathered tuffs are studied by X-ray fluorescence (XRF). The physical properties of the weathered tuffs are studied through dry and saturated unit weight, effective porosity, and water absorption.

The field investigation performed in the study area reveal that the fairy chimneys, which are partially

covered by lichens and cut by joints, show clear effects of weathering. Since the weathering products are

also protected in those places, field studies are concentrated to find such typical locations in the study

area in order to determine the state and depth of weathering. Two block samples from Ortahisar (lichen­covered) and OrgUp (iron-stained) were collected (Figure 1). The sizes of the block samples were so selected that they fully incorporate the weathered zone.

225

3.1. Mineralogical and Petrographical Properties of the Weathered Cappadocian Tuff

3.1.1. Optical Microscopy

For the mineralogical and petrographical analyses, polarizing optical microscope was used. Several thin sections were systematically prepared from the two block samples to provide a continuous view of the tufts from both lichen-covered and iron-stained surfaces to a depth of 23 cm.

In the lichen-covered sample, slight mechanical and very little chemical weathering of the minerals are observed within the upper 2 cm of the sample. Plagioclase feldspars are slightly fractured at this zone. The cleavage planes of the feldspars and biotites are widened due to weathering . According to M.E.T.U. (1987), lichens play a very important role in deterioration of tufts within this zone. Biotites and rock fragments, however, are slightly discolored forming iron oxide staining at this depth. The effect of mechanical weathering decreases with depth and ceases almost at a depth of 8 cm whereas no chemical weathering can be observed after 2 cm depth. In the iron-stained sample, slight mechanical and chemical weathering of the minerals are also noted within the first 2 cm of the sample nearer to the joint surface. In this zone, plagioclase feldspars are slightly fractured. Biotites are highly discolored forming iron oxide staining so that the outer boundary of the minerals can hardly be traced. Their cleavages are widened. On the other hand, the rock fragments are also discolored. The effect of mechanical weathering decreases with depth and ceases almost at a depth of 10 cm whereas chemical weathering in the form of discoloration in biotites and in rock fragments, extends laterally about 17 cm from the joint surface with decreasing intensity. In the field, however, discolored zone of up to 20 cm was observed (Topal and Doyuran, 1994)

3.1.2. Methylene Blue Adsorption Test The methylene blue adsorption test is performed to obtain information on the presence and properties of clay minerals in the lichen-covered and iron-stained samples. The spot method proposed by AFNOR (1980) is used during the test. The description of the methylene blue adsorption test procedure, as well as the methylene blue adsorption value (MBA) and the cation exchange capacity (C.E.C.) of the lichen­covered and iron-stained samples are presented in Topal (1996). Based on the test results, the lichen­

covered sample has 2-7% smectite whereas iron-stained sample has 7.5-14% smectite.

3.1.3. X-Ray Diffraction The X-ray diffraction (XRD) analyses are performed on both lichen-covered and iron-stained samples to assess abundance of all minerals and the types of clay minerals within the tufts. The sampling depths are selected on the basis of the methylene blue adsorption test results. The depths of samples from the source of alteration are 0-0.5 cm, 0.5-1cm, 1-1.5 cm, 1.5-2 cm, 3-4 cm, 5-6 cm, 8-9 cm, 11-12 cm, 15-16 cm, and 22-23 cm. For the XRD analyses, 20 samples are obtained by scratching on the two block

samples in the laboratory from the surface to a depth of 23 cm. The scratched samples are then powdered to pass through 200 mesh. Two kinds of samples are prepared from each sample for the analyses, namely unoriented and oriented samples. The oriented samples were tested after air-drying,

glycolation, and heating at 300°C. The XRD results of the lichen-covered samples yield similar diffraction patterns. A typical XRD analyses

of the lichen-covered sample corresponding to a depth of 0.5-1 cm is shown in Figure 2. The XRD analyses of the unoriented lichen-covered samples reveal that very small peaks of clay minerals exist within the tuft samples other than dominantly feldspar, some quartz, and small amounts of mica minerals (Figure 2A). The oriented XRD analyses, however, indicated mainly the smectite-type clay minerals with

minor quantity of illite (mica) (Figures 2B,C,D). The XRD results of the iron-stained samples also yield diffraction patterns very similar to those of the

lichen-covered samples. The XRD analyses of the unoriented iron-stained samples indicate the presence of dominantly feldspars, quartz, mica, and clay minerals. The oriented XRD analyses show the smectite­

type clay minerals. The clay mineral peak on the unoriented XRD pattern of the iron-stained sample corresponding to a depth of 0-0.5 cm has slightly higher intensity than the others. This is attributed to the

existence of relatively higher clay content near the joint surface.

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In both samples, the tuff matrix is partly altered to smectitic clay. The smectitic clay is not only found at

the weathered zone but also away from it. So, the alteration of volcanic glass to smectitic clay has

probably started after the deposition of the tuffs even before the formation of the fairy chimneys. Besides the alteration of volcanic glass, some of the rock fragments are also highly altered to clay minerals, giving rise to discoloration and fractures when they are in contact with water. Therefore, the

mineral contents of an altered rock fragment which caused tension cracks on the samples are also determined by XRD method (Figure 3). The unoriented XRD peaks reveal the presence of dominantly clay (smectite), feldspar, and quartz (Figures 3A). The oriented XRD peaks (air-dried, glycolated, and heated), however, show mainly smectite with very small amount of kaolinite (Figures 38, C, D ).

Therefore, fractures are attributed to swelling of smectite.

1•, I Q•

I I \, i I

.1 l I I I I

!

"' ,. )0

,,. C."-

..

I .,

18 CuK-

(A) Unoriented \

I I I I

<O '° ..

(C) Glycolatcd I

..

'"• I i

~, j \,., \

I ~

(B) Air-dned I

•·,-------------(0) Heated \ !

I I I

f\~~\ I \ .

' ~ ' r • t "C> 11 n 1J w. ~ ,,. c .....

Fi~re 2. !ypic~ ~-~ay diffraction patterns for the lichen-covered sample (0.5-1 cm) (S. Smectite, B. B1ottte, F: Feldspar, Q: Quartz, I: Illite).

,. (A) Unorientcd (B) Air-dned

" I

~..;.:J. \ \,._

lO .. lO )0 "' ,. '-"- XI Cw14-

,.I 1l s

(C) Glycolated \ r !\ (D) Heated \

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Figure 3. X-ray ?i~action patterns of altered rock fragments (S: Smectite F· Feld Q· Quartz, K: Kaobrute). ' · spar, .

227

3.2. Chemical Properties of the Weathered Cappadocian Tuff

Chemical weathering of rocks may result changes in initial elemental concentrations by leaching and enrichment (Borchardt et al., 1971; Borchardt and Harward, 1971 ). In order to determine the depth of chemical weathering, major element concentrations in percent, from the source of alteration (lichen and joint surface) at ten different depths from each block sample (a total of 20 samples) are determined by means of X-ray fluorescence (XRF) (Tables 1-2). These analyses were carried out at the laboratory of Leeds University in U.K. Because chemical weathering is more pronounced near the source of alteration, much closely spaced samples were collected from the highly altered zones. The depths of samples from the source of alteration are 0-0.5 cm, 0.5-1 cm, 1-1 .5 cm, 1.5-2 cm, 3-4 cm, 5-6 cm, 8-9 cm, 11-12 cm, 15-16 cm, and 22-23 cm. These depths correspond to the same depths of samples taken for XRD.

Since the weathering products derived from the fresh tufts are of major interest, analytical data are normalized by dividing each elemental compositions of every sample by the same elemental composition of the fresh tuft sample. For this purpose, the tuft sample obtained at a depth of 22-23 cm of the lichen-covered sample is considered to be a reference sample. So, all the analyses belonging to other depth intervals are normalized to this sample. This permits easy comparison of the two block samples and of different weathering zones of each tuft. The relative contents (normalized values) of each major element of both lichen-covered and iron-stained samples, are plotted against depth in Figure 4. Since the sampling points correspond to a range of depths (e.g. 3-4 cm). an average depth is used during the plotting of the graph. Considering the fact that the weathering proceeds horizontally in the fairy chimneys, the depth of analysis of every element is shown in abscissa of the graph.

Table 1. Major element analyses of the lichen-covered samples.

Depth (cm) 0-0.5 0.5-1 1-1.5 1.5-2 34 5-6 8-9 11-12 16-17 22-23

Si~ 68.43 72.66 73.42 73.81 73.35 73.24 73.40 73.52 73.19 73.49

Ti~ 0.18 0.17 0.17 0.17 0.18 0.19 0.18 0.19 0.18 0.19

Al2~ 12.26 12.34 13.01 13.11 13.24 13.38 13.31 13.22 13.31 13.35

F4'.2._~ 1.30 1.16 1.12 1.14 1.15 1.14 1.11 1.17 1.15 1.16

MnO 0.05 0.06 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05

MgO 0.77 0.69 0.53 0.42 0.38 0.39 0.33 0.38 0.33 0.36

Cao 2.43 1.87 1.75 1.74 1.79 1.82 1.78 1.77 1.80 1.77

N"_20 1.94 2.11 2.24 2.19 2.25 2.33 2.28 2.31 2.39 2.29

K20 3.51 3 .64 3.83 3.90 3.95 3.93 3.93 3.98 3.94 3.88

~% 0.05 0.03 0.02 0.02 0.02 0.03 0.02 0.02 0.03 0.02

L.o.I. 9.48 5.15 4.10 3.99 4.05 3.93 3.59 3.52 3.81 3.57

Total 100.39 99.88 100.25 100.56 100.42 100.42 99.99 100.13 100.18 100.15

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Table 2. Major element analyses of the iron-stained samples.

Depth (cm) ~.5 0.5-1 1-1.5 1.5-2 3-4 5~ 8-9 11-12 16-17

Si~ 70.03 70.47 70.72 71 .33 71.45 71.33 71.42 72.18 72.38

Ti0...2.. 0.17 0.18 0.18 0.19 0.18 0.19 0 .19 0.19 0.19

~0...3. 12.98 13.27 13.57 13.74 13.72 13.63 13.81 13.82 13.73

F~~ 4.98 4.20 3.10 2.89 2.78 2.36 1.68 1.74 1.57

MnO 0.05 0.05 0.06 0.06 0.07 0.10 0.09 0.08 0.12

MgO 0.52 0.45 0.46 0.40 0.40 0.40 0.40 0.40 0.38

Cao 2.01 1.96 1.96 1.95 1.93 1.87 1.88 1.83 1.84

N~O 2.18 2.13 2.58 2.27 2.34 2.38 2.31 2.33 2.35

__&o 3.40 3.52 3.70 3.71 3.80 3.80 3.92 3.96 4.00

~~ 0.02 0 .02 0.02 0.02 0 .02 0.02 0.02 0 .02 0 .03

L.o.I. 4.18 3.83 3.91 3.78 3.84 3.92 3.77 3.83 3.93

Total 100.53 100.08 100.27 100.33 100.53 99.99 99.50 100.38 100.53

21" ~ -~-~------------------~Loi

1 {~' 1~ ------- --------- - ---- - 1(20

j.

f-1i

z ,J u; f-

r~ z 0 u (.l..)

> 1 .... r=

------- --------------- Na~O

- -------tL=-=..'.=---------- --------- M aO

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Al203

, I Ti02

1 J S10 2

O· 0 , 4 6 8 10 1 2 1 4 1 6 1 8 iG 22 24

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Figure 4. Comparison of major element concentrations of the lichen-covered (solid lines) and iron-stained (dashed lines) samples.

22-23

72.29

0.21

13.87

1.44

0 .06

0.42

1.87

2.44

3.98

0.02

3.98

100.57

The relative content variations of major elements of the lichen-covered samples (solid lines) with depth indicate that significant enrichment of MgO, Cao, P20 5, and L.o.I occurs within the upper 2 cm of the

weathering zone. The other elements do not change significantly (Figure 4). In the case of the iron­stained samples (dashed lines), however, a significant Fe20 3 and very little MgO enrichments within the first 2 cm of the joint surface are observed. Fe20 3 enrichment extends almost laterally to 17 cm depth (Figure 4). This depth is also determined from the discoloration of the sample observed in the field and under the microscope. Such reddish color is attributed to Fe20 3 development. Similar reddish color

229

deteriorating the wall paintings also exists in some of the churches in the area. MnO in these samples, however, fluctuates with depth.

If we compare both the lichen-covered and iron-stained samples, the lichen-covered sample has more enrichment in MgO, P20 3, and Lo.I. On the other hand, the iron-stained sample has more Fe20 3

enrichment (Figure 4). Excepting Fe20 3, all the variations within the samples are confined almost to the upper 2 cm of the weathering zones (Topal and Doyuran, 1994).

Evaluation of the analyses indicates that the depth of weathering in the lichen-covered and iron-stained tufts is about 2 cm from the source of alteration. However, discoloration may extend laterally upto 17 cm in the case of the iron-stained tuff.

The gains and losses of the major elements of the tuff samples are also used to determine the depth of of weathering. They are calculated using a method described by Krauskopf (1967, p.100). This method is based on the assumption that alumina content does not change appreciably during chemical weathering. The results of these calculations are given in Tables 3 and 4.

Table 3. The percentage gain or loss of each major element of the lichen-covered samples.

Depth (cm) 0-0.5 0.5-1 1-1.5 1.5-2 3-4 ~ 8-9 11-12 16-17 22-23

Si~ 1.39 6.91 2.49 2.25 0.59 -0.55 0.19 1.02 -0.16 0.00

Tl~ 5 .26 -5.26 -10.53 -10.53 -5.26 0.00 -5.26 0.00 -5.26 0.00

Al~ 0.00 0.00 0.00 0.00 0 .00 0.00 0.00 0.00 0.00 0.00

F~ 21 .55 7.76 -0.86 0.00 0.00 -1.72 -4.31 1.72 -0.86 0.00

MnO 0.00 20.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

MgO 133.33 105.56 50.00 19.44 5.56 8.33 -8.33 5.56 -8.33 0.00

CaO 49.15 14.12 1.69 0.00 1.69 2.26 0.56 1.13 2.26 0.00

Na:zO -7.86 -0.44 0.00 -2.62 -1 .31 1.31 -0.44 1.75 4.80 0.00

K20 -1 .29 1.55 1.29 2.58 2.58 1.03 1.81 3.62 1.81 0.00

P:z05 150.00 50.00 0.00 0.00 0.00 50.00 0.00 0.00 50.00 0.00

L.o.I 188.80 55.74 17.65 13.73 14.01 9.52 0.84 -0.56 6.72 0.00

Table 4. The percentage gain or loss of each major element of the iron-stained samples.

Depth (cm) 0-0.6 0.5-1 1-1.6 1.5-2 3-4 6-6 8-9 11-12 16-17 22-23

Si~ -1 .99 -3.56 -5.30 -5.68 -5.42 -4.95 -6.05 -5.15 -4.25 -5.34

Ti~ -5.26 -5.26 -5.26 0.00 -5.26 0.00 -5.26 -5.26 0.00 5.26

Al~ 0.00 0.00 0.00 0 .00 0.00 0.00 0.00 0.00 0.00 0.00

Fe:z03 340.52 263.79 162.07 141 .38 133.62 99.14 39.66 43.97 31 .03 18.96

MnO 0.00 0 .00 20.00 20.00 40.00 100.00 80.00 60.00 140.00 20.00

MgO 50.00 25.00 25.00 8.33 8.33 8.33 5.56 8.33 2.78 13.88

Cao 16.38 11 .30 8.47 6.78 6.21 3.39 2.82 -0.56 1.13 1.69

Na:zO -2.18 -6.55 10.48 -3.93 -0.44 1.75 -2.62 -1.75 -0.44 2.62

K:zO -9.82 -8.53 -5.94 -6.98 -4.65 -3.88 -2.33 -1 .29 0.26 -1 .03

P:zOg 0.00 0.00 0.00 0.00 0.00 0 .00 0.00 0.00 50.00 0.00

L.o.I 20.45 7.84 7.56 2.80 4.48 7.28 1.96 3.64 7.00 7.28

230

The gain-loss calculations of the lichen-covered samples suggest a significant increase in the Lo.I., P20 5, and MgO near the surface. Cao and Fe20 3 values are slightly increased near the surface.

They generally decrease with depth. The other major elements are not significantly changed. In the case of the iron-stained samples, Fe20 3 values near the joint surface show a very significant increase. Although it decreases with depth, it has still a relatively high values at a depth of 22-23 cm. On the other hand, some increase in MgO and Lo.I., as well as very small increase in Cao may also be observed. Mn considerably fluctuates with depth. The other elements are not significantly affected

from chemical weathering. If the results of gain-loss calculations of both lichen-covered and iron-stained samples are compared with the relative contents of the major elements (see Figure 4), both methods yield identical results.

3.3. Physical Properties of the Weathered Cappadocian Tuff

The effect of deterioration on the physical properties of tufts is investigated by determining the variations of dry and saturated unit weight, effective porosity, and water absorption through the weathering zones. The core samples of 25 mm diameter are extracted from the block samples at 4 different depths and the tests are performed on these samples in accordance with 1.S.R.M. (1981),

RILEM (1980), and TS699 (1978). The test results are given in Tables 5 and 6.

Table 5. Physical properties of the lichen-covered samples.

Depth (cm) 0-3 4-7 8-11 20-23

Dry Unit Weight, kNJm3 13.5 13.6 13.5 13.6

Sat. Unit Weight, kNtm3 17.6 17.6 17.6 17.6

Effective Porosity, % 41 .1 40.8 40.8 40.5

Water Absoption (by weight),% 20.9 20.6 20.7 20 .8

Table 6. Physical properties of the iron-stained samples.

Depth (cm) 0-3 4-7 8-11 20-23

Dry Unit Weight, kN/m3 13.7 13.6 13.6 13.5

Sat. Unit Weight, kNJm3 17.6 17.6 17.6 17.5

Effective Porosity, % 39.9 39.9 39.9 40.1

Water Absorption (by weight),% 21 .7 21 .9 22.0 21 .8

Based on the test results, no significant change in physical properties from the source of alteration to the fresh part of the tufts is observed. Although the samples are taken from the area where the weathering products are well preserved, the small size of the rocks tested may enhanced the heterogeneity. It is also possible that some weathered portion may be removed from the surface of the fairy chimneys. Therefore, similarity of the physical properties of the weathered tufts may suggest relatively fresh state of the samples recovered.

4. ENGINEERING SIGNIFICANCE OF THE WEATHERED ZONES

The investigation of the physico-chemical properties of the weathered Cappadocian tuff reveals that

the products of the mechanical weathering are rarely observed. Most of the products are readily eroded away. The chemical weathering can be observed within the first 2 cm of the lichen-covered surface and extends laterally up to 20 cm from the joint surface. The chemical weathering of the volcanic glass of the tuff produces smectite-type clay mineral which swells upon wetting and shrinks upon drying. The clay content is relatively high around joints. The joints also cause instability problems for the churches dwelled within the fairy chimneys in the study area. It is the usual engineering practice to install rock bolts in order to secure stability. However, the higher amount of clay content around joints may produce higher swelling pressures. Therefore, the differential swelling

231

pressures which may be developed within the jointed fairy chimneys, should be considered during the design of rock bolts.

The highly altered rock fragments produce smectite-type clay mineral. Secondary cracks may be developed around the altered rock fragments if the swelling pressure exceeds the tensile strength of the tuff at any time. Although the cracks formed in this manner may be local, they allow the water to migrate within the fairy chimneys thus promoting deterioration.

The joints and artificial cracks due to dwelling are also the places where rainwater seeps and causes discoloration of the wall paintings of the churches by chemically altering the biotites and the rock

fragments present within the Cappadocian tuff. This is also an indication of the presence of oxidizing environment. In such an environment, the rock bolts used to secure the blocks may be corroded. Corrosion of the rock bolts causes further discoloration and deterioration. Thus, the rock bolts if used, should be non-corrosive type.

5. CONCLUSION

In the Cappadocian tuff, the products of mechanical weathering are easily eroded away. Therefore, the observed mechanical weathering is minor and in micro-scale. It totally ceases within first 8-10 cm. On the other hand, chemical weathering is limited to the upper 2 cm in the case of lichen-covered surfaces, and 20 cm adjacent to joints. The oxidation of biotites and rock fragments causes discoloration of the tuff. The alteration of volcanic glass and rock fragments produces smectite-type clay mineral. The clay content is higher adjacent to joints and lower where lichen cover exists. Therefore, a differential strain and associated swelling pressure may be developed around joints. The

differential swelling pressure development around joints and the formation of tension cracks around altered rock fragments may be expected. There is also a potential for further oxidation of biotites and rock fragments around joints. Therefore, the use of iron-containing materials should be avoided

during conservation studies.

ACKNOWLEDGEMENT

This study is financially supported by METU Research Fund Project (AFP).

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volcanic ash soils in Oregon, Clays and Clay Minerals. Vol. 19, pp.375-382. Borchardt, G.A. , and Harward, M.E. , 1971 , Trace element correlation of volcanic ash. Soil Sci. Soc. Am. Proc.,

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Suggested Methods, Pergamon press, Oxford, 211 p. Krauskopf, K.B., Introduction to geochemistry, McGraw Hill, New York, 721 p. L'Association Francaise De Normalisation (AFNOR), 1980, Essai au bleu de methylene, P1 8-592, AFNOR

80181 , Paris La Defence. Loughnan, F.C., 1969, Chemical weathering of the silicate minerals, Elsevier, NewYork,154 p. . M.E.T.U., 1987, Investigation of the mechanisms of stone deterioration for the purpose of conservation of

Goreme tufts, Progress report, Middle East Technical University, 61 p. . . . . . Pasquare, G., 1968, Geology of the Cenezoic volcanic area of Central Anatolia, Acedem1a Naz1onale De1 Lmce1,

Roma, Vol.9, Serie 8, Fasc. 3, Roma, pp.57-201. . R.l.L.E.M., 1980, Recommended tests to measure the deterioration of stone and to assess the effectiveness of

treatment methods, Commission 25-PEM, Material and Structures, Vol.13, pp.175-253. . Topal, T., 1996, The use of methylene blue adsorption test to assess the .cla~ content of the Cappadoc1an tuft,

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