International Research Journal of Applied and Basic Sciences. Vol., 3 (2), 383-389, 2012
Available online at http://www. irjabs.com
ISSN 2251-838X ©2012
Investigation of mineralogical properties of soils developed on pyroclastic deposits;
A case study from Karaj region, Iran
Alireza Raheb*, Ahmad Heidari and Athar faghih
Department of Soil Science Engineering, Faculty of Agricultural Engineering and Technology, College of
Agriculture & Natural Resources, University of Tehran, Karaj, Iran
*
Corresponding author: Alireza Raheb, E-mail: [email protected]
ABSTRACT: The study of soils derived from volcanic products because their large extent
and unique characteristics are very important and can help us in the management and
identification capabilities of them. Clay minerals are among the most important indicators
of soil evolution via influencing a widerange of physical and chemical characteristics.
Relationships between clay mineralogy suite and soil parent materials are keys to
distinguish between inherited and neoformed minerals. Samples from surfacial soils of
more than 40 sites at different topographic and climatic positions of the studied area were
selected, described and analyzed.Some physical, chemical and mineralogical characteristics
of samples were determined using standard methods. The aims of this study are
investigation of clay mineralogy of soils formed on Karaj-green-tuff and their
physicochemical properties under different topographic and climatic conditions.The results
showed that although weathering the pyroclastic parent material has caused to formation of
mixed clay minerals, chlorite, illite, vermiculite, smectite and kaolinite, but
physicochemical properties of the studied soils including sandy soil texture (regarding to
limited dispersion due to the existenec of short-rang-order minerals) with high cation
exchange capacity demonstrate that the main properties of the studied soils have originated
from pyroclastic materials.
Keywords: Clay minerals; Parent material; Soil genesis and classification; Volcanic ash;
Weathering
Abbreviations: Al- Alominium; CEC- Cation Exchange Capacity; CDB- Citrate
Dithionate Bicarbonate; EC- Electrical conductivity; HI- Hidroxy interlayer; OC- Organic
Carbon; PSD- Particle Size Distribution.
INTRODUCTION
Recognition and study of different kinds of clay minerals and their evolution process may guide
us to scientific soil management. Knowledge of clay mineralogy is crucial to understanding soils'
nutritional status and nutrient-supplying power (Surapaneni et al., 2002). Understanding weathering as a
process requires a knowledge of the nature and distribution of clay minerals as one of its principal
products (Duzgoren-Aydin et al., 2001). Volcanic ash soils cover about 0.84% of the world’s land area
(Dahlgren et al., 2004). Volcanic parent materials, specially pyroclastic rocks like tuff (kind of pyroclastic
rocks more than 75% of whose particles length are less than 2 mm), are weathering sensitive. Soils
derived from volcanic deposits exhibit unique physical and chemical properties, such as low bulk in
which halloysite is the dominant clay mineral where density, high water retention, variable charge
characteristics, and strong phosphate sorption, which have been largely ascribed to active amorphous
weathering products, such as allophane, imogolite, and Al–
et al., 2000). Displacment of weathering products causes to accumulation of short-range-order minerals
and stable organo-mineral complexes which are the most important factors in soil formation on volcanic
Intl. Res. J. Appl. Basic. Sci. Vol., 3 (2), 383-389, 2012
materials. Under Mediterranean and semi arid climates, the most common secondary minerals formed by
weathering of tuff formations are halloysite and allophone (Ezzaim et al., 1999).
Zehetner et al. (2003) stated that specific environmental conditions, such as the eruption histories of
surrounding volcanoes, the composition of volcanic ejecta, present-day climate, as well as paleoclimate
and glaciation history are very important in weathering and development of volcanic ash soils exist in
different parts of the world.
The influence of clay minerals on soils chemical and physical charaterstices like CEC, water holding
capacity, soil fertility, aereation, etc. is of great importance. Many studies have been performed on the
mineralogy of soils resulted from volcanic materials all over the world (Lamrux et al., 1973; Pelankon et
al., 1977; Okamora and Vada, 1989; Soma et al., 1992; Shoji et al., 1993). The general result of this
studies shows that clay mineralogy of soils formed on pyroclastic materials affected by different factors
such as parent material, soil formation processes, soils pH, soil moisture, thickness of surface sediments
and organic materials accumulation. Duzgoren-Aydin et al. (2001) reported that the distribution of clay
minerals along a weathered profile developed over crystal-vitric tuffs are examined by X-ray
diffractometry (XRD) techniques. Bish (1989) stated that the clay minerals in Yucca Mountain tuffs in
south-central Nevada are predominantly interstratified illite/smectites, with minor amounts of chlorite,
kaolinite, and interstratified chlorite/smectite. At present very little studies have been performed on
mineralogy of soils resulted from tuff and pyroclastic materials in Iran where tuff is mostly studied from
geological point of view. Among very little studies, Taghipoor (2003) studied the mineralogy of zeolitic
tuffs of Karaj formation, and reported the prevalence of minerals such as kaolinite and muscovite. The
aims of this study were to investigate the mineralogy of soils formed on Karaj-Green-Tuff and their
physicochemical properties under different topographic and climatic conditions.
MATERIAL AND METHODS
Study Area
The studied area is located in the southern highlands of Alborz in north of Iran (between 36º 3 to 36º 9
of northern latitudes and 51º 7 to 51º 22 of eastern longitudes) (Figure1). The height of the region
varies between 2300 to 2879 m and its slope varies between 20 to70% . The mean annual precipitation is
about 440 to 560 mm due to height and mean annual air temperature varies between 3.5 to 7.8 ºC. The
prevailing vegetation cover includes Graminea, Artmezia, Grasses, which covers about variation 25 to
50% of grounds surface in different parts. From geological view the region is mostly composed of Karaj
formation (including pyroclastic materials, shale, silliceous and calcareous sediments, green tuff,
tuffaceous shale, crystalline tuff, volcanic ash and green tuffite) (Ahmadi and Feiznia, 2006).
Field Sampling
The surface soil samples selected from more than 30 points of different situations were described and
analyzed and 5 sampels were selected for further mineralogical studies.
Physico-Chemical Analysis
All analyses were performed on air-dried soil samples passed through a 2 mm sieve (Pansu and
Gautheyrou, 2006). The samples' physicochemical and mineralogical
characteristics were analyzed according to standard methods (Kunze and Dixon, 1986). pHsp was
determined using a pH meter applied to soil saturated to a paste using deionised water. Electrical
conductivity (ECse) was also measured in the saturated extracts. Particle size distribution was measured
by the hydrometer method (Carter and Gregorich, 2008). Organic carbon was determined using wet
oxidation (Pansu and Gautheyrou, 2006). Cation exchange capacity (CEC) was measured by the
ammonium acetate method (pH=7) (Carter and Gregorich, 2008).
Mineralogical Analysis
Clay mineralogical studies were performed by removing soluble salts and gypsum by washing out (Konse
and Rich, 1959), carbonates by neutralization with sodium acetate (pH=5) (Grossman and Millet, 1961),
organic materials by oxidation with H2O2 (Konse and Rich, 1959) and ferrous oxides by citrate dithionate
bicarbonate (CDB) (Mehra and Jackson, 1960). Clay fraction was separated by sedimentation and
saturated with Mg2+ and K+ ions using 1 N MgCl2 and KCl solutions. Mineralogical composition was
determined by X-ray diffraction using a Siemens D5000 diffractometer via CuK ( =1.5409 Aº) and 30 kV
voltage and 30 mA.
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Intl. Res. J. Appl. Basic. Sci. Vol., 3 (2), 383-389, 2012
Figure 1. Map of studied region in Alborz province, Iran
RESULTS AND DISCUSSION
Regarding to the mountainious conditions and intense slope of the region and the results of
physical and chemical charactristics of soil samples, it was revealed that, all of the studied soil
samples show low evolution (Entisols to Inceptisols). Table 1 shows some physico-chemical
characteristics including PSD, pH, OC and CEC. pH of the saturated pastes was around neutral to
slightly alkaline (6.61- 8.3) and electrical conductivity of saturated extracts (ECe) ranged between
0.69 and 2.9 dS m-1 (Table 1). The organic carbon content showed a considerable variation from
0.11 in sample No.17 (high elevation) to 4.48 in sample No.20. Organic matter contents decrease
with decreasing elevation, presumably because of less additions in cultivated land and more rapid
decomposition due to higher temperatures and higher pH values. CEC was influenced by the clay
content, clay minerals type and organic matter content. CEC ranged between 2.02-38.33 cmol+kg-1
and clay content in this study varied between 1.56 to 31.72 percent, while CEC /% Clay ratio
chenged between 0.19 to 8.
Clay mineralogical composition was determined using the intensity and position of the X-ray
diffractogram peaks, considering clay apparent CEC (CEC/Clay %). The intensity of 1.43 and 0.71 nm
peaks in Mg-saturated and Mg-saturated, glycerol-solvated treatments, and the collapse of the peaks in Ksaturated and K550 treatments demonstrate the presence of vermiculite (Figure 2). Also, the high
intensity of 1.0, 0.5 and 0.33 nm peaks in Mg-saturated diffractograms indicates the presence of illite.
Kaolinite was detected based on the presence of 0.71 and 3.56 nm peaks in Mg-saturated treatment that
collapsed in K550 treatment. A weak shifting 1.43 nm peak in the Mg-saturated treatment toward 1.8 nm
in Mg saturated-glycerol solvated treatment also indicated the presence of some expandable clay minerals
(smectites). A shifting 1.43 nm peak toward 1.1-1.3 nm in K550 treatment showed the presence of
hydroxy-interlayered minerals. XRD diffractograms showed that:
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Intl. Res. J. Appl. Basic. Sci. Vol., 3 (2), 383-389, 2012
Illite > chlorite > smectite > kaolinite and vermiculite are the most abundant clay minerals, respectively
(Table 2). In addition mineralogical analysis of tuff samples shows that Chlorite, Quartz and Illite are
dominant minerals related to the Karaj-Green-Tuff (Figure 2, D).
Table 1. Some physical and chemical properties of studied soil samples
Texture %
pH
EC
CEC
CEC/
dS/m
Cmol+/Kg
%Clay
Sand
Silt
Clay
OC
%
1
34.44
46
19.56
7.7
2.52
12.75
0.65
0.49
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
62.44
59.72
61.72
64.44
65.72
61.72
61.72
64.28
58.44
63.72
46.44
52.28
58.28
76.44
76.44
44.28
62.44
50.28
38.44
77.2
80.28
83.72
86.44
44.28
56.44
24.28
39.72
36.44
70.28
28
34
30
18
26
28
15.48
24
32
24
34
38
32
16
16
40
24
32
46
18.52
14
14
12
43.86
24
44
38
36
24
9.56
6.28
8.28
17.56
8.28
10.28
22.8
11.72
9.56
12.28
19.56
9.72
9.72
7.56
7.56
15.72
13.56
17.72
15.56
4.28
5.72
2.28
1.56
11.86
19.56
31.72
22.28
27.56
5.72
8.1
8
7.9
8
7.57
8
8.1
7.9
7.8
8
7.9
8.3
7.9
7.9
8.1
8
8.01
7.98
7.39
7.43
7.46
6.61
7.95
7.69
8.06
7.78
7.64
7.97
7.76
1
1.22
1.35
0.71
0.91
2.35
1.72
2.64
1.15
1.15
2.58
2.37
1.3
0.74
2.21
1.12
0.69
2.72
1.25
1
1.52
1.8
1.08
1.87
2.9
1.5
1.6
2.4
0.7
10.44
11.17
17
4.08
6.71
2.02
5.05
16.1
2.36
4.17
14.7
16.28
17.18
12.65
9.27
10.53
15.22
15.22
18.65
10.69
13.49
16.28
12.46
18.65
38.33
24.68
16.28
13.32
13.27
1.09
1.78
2.05
0.23
0.81
0.19
0.22
1.37
0.24
0.34
0.75
1.67
1.76
1.67
1.22
0.67
1.12
0.86
1.2
2.5
2.35
7.14
8
1.57
1.96
0.78
0.73
0.48
2.32
0.49
0.78
0.47
0.51
1.52
1.47
0.6
0.6
2.37
0.47
0.54
1.43
0.83
1.5
0.92
0.11
0.54
0.65
4.48
2.37
0.36
0.6
0.47
0.67
1.47
2.35
2.06
0.76
0.81
Sample
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Intl. Res. J. Appl. Basic. Sci. Vol., 3 (2), 383-389, 2012
1.4 nm
A
B
1.4 nm
1 nm
0.7 nm
1 nm
0.7 nm
mgg
mgg
mg
k
kt
mg
k
kt
0.336 nm
C
D
mgg
k
1.4 nm
mg
1 nm
0.563 nm
1.01 nm
0.7 nm
0.259 nm
kt
Figure 2. Representative X-ray diffractograms: A: Sample no. 4, B: Sample no. 18, C: Sample no. 23 , D:
Tuff Sample.
sample
Table 2. Relative abundance of some soil clay minerals at studied region
smectite
vermiculite
kaolinite
illite
chlorite + HI
mixed
4
++
+++
+
++
+
+
14
+++
+
+
+++
++
-
18
++
+
+
++
++
++
22
+
-
+
+++
+++++
-
23
+
+
+
+++
+++
-
Tuff
-
-
-
++
+++
++++
Illite and chlorite are found to be the prevailing minerals in the studied samples. These two minerals are
reported in clay fraction of soils from Iran and the other regions of world, their existence being often
attributed to the weathering of parent materials of soils with little evolution. Since they are the prevailing
minerals in Karaj-green-tuff, its can be concluded that their existence source is geogenic. On the other
hand, climatic and physiographic characteristics, low temperature and therefore, low weathering speed
could also satisfies this idea. Khademi and Jalalian (1992), and Hassannezhad and Khormali (2007), also,
reported the existence of illite and chlorite in soils of Iran to be geogenic. Relative amount of Chlorite
and Hidroxy interlayer increases with increasing height due to soil erosion and being young soil surface.
Duzgoren-Aydin et al. (2002) in study of distribution of clay minerals along a weathered pyroclastic soils
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Intl. Res. J. Appl. Basic. Sci. Vol., 3 (2), 383-389, 2012
in Hong Kong reported that chlorite and illite are the most abundant clay minerals in fresh and moderately
decomposed rocks, respectively.
There were some smectite and vermiculite in most of the studied samples. These minerals are very low
due to lack of restricted drainage conditions and existence of unsuitable soils other chemical and physical
characteristics such as low electrical conductivity, low pH, low among of soluble anions and cations for
their stability. Another attractive point is that the quantity of Smectite decrease as the height increases,
that can be under direct affect of tempreture, reduction and dilution of soil extract by precipitation and
slope increase. Chichester and Partners (1969) and Lamrox et al. (1973) performed simillar studies on
soils resulted from pyroclastic materials. They reported the existence of smectite and attributed its
variability in the soil to the precipitation and the tempreture.
On the other hand, since the parent materials comprises mostly of chlorite, it can be concluded that
vermiculite should possibly be the result of chlorites weathering. Kaolinite was also found in
mineralogical composition of the samples under study and with regard to the regions conditions, its
existence should be geogenic. According to the export made by Khademi and Jalalian (1992), the
formation of kaolinite through soil formation processes in Iran dry zones is impossible. Kaolinite can
show a wide range of structural disorder in pyroclastic soils due to primarily to Al vacancy displacements
in the octahedral sheet (Soma et al., 1992). Irfan (1997) claimed that, some kaolin occurrences were
related to hydrothermal activity. The recent works, however, by Parry et al. (2001) and Churchman et al.
(2001) suggested that, the majority of kaolin occurrences and their distribution are related to weathering
processes and that hydrothermal alteration is only locally important.
It is concluded that, the nature, type and abundance of clay minerals along the profile result from complex
combinations of several different processes controlled mainly by three factors: the pre-weathering
alteration history of parent rock, the degree of weathering, and microenvironmental conditions. Climate is
considered the overriding factorble for the observed altitudinal differences in soil develeopment.
Differences in rainfall and evapotranspiration resulting in different leaching regimes are believed to have
caused the differential formation of clay minerals and thus the differential development of soil properties.
Temperature has further affected organic matter decomposition causing increased accumulation with
elevation and thus resulting in the altitude dependent formation of different soil charactristic.
However, the measured clay contents are low incontrary to apparent CEC and activity classes of the
studied soils. In other words, comparing of the apparent CEC of the soil samples with the mineralogy
results, it was found that there is a contradiction between the estimated relative quantity of minerals in the
studied diffractograms with the results gained from measuring the soils apparent CEC. According to
possible existence of amorphous minerals such as allophane and Al-Hummos complexes in soils formed
on volcanic parent materials, has lead to limited dispersion in this soils and therefore, clay is under
estimated in this soils and this has coused the contradiction between clay percentage and CEC.
Accordingly, it seems that mineralogical study of soils with volcanic characteristics would not be possible
by studying only the XRD results. The results of XRD should be accompanied with the results of other
kind of studies including scanning electronic microscope (SEM) studies and thermal analysis.
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