This article is based on research supported by the JSPS KAKENHI (16300292; principal investigator: Y. Matsukura) and the Sasakawa Scientific Research Grant (held by W. Song) from the Japan Science Society. The manuscript was greatly improved by thoughtful and precious comments by the two anonymous referees. We deeply thank the referees.And we also thank Dr. Samuel Etienne for the French translation and his great support, Dr. T. Hattanji for his precise comments andkind support, and all the coordinators of this journal for their efforts.
1Processes of rock weathering are usually classified into three types: physical weathering (pressure release; wet-dry slaking; frost shattering and thermal expansion), chemical weathering (dissolution; hydrolysis; oxidation) and biological weathering (chelation by plants; microbial activities). Among various biological weathering agencies, the important role of microorganisms in rock weathering or mineral alteration has been highlighted previously (e.g., Ehrlich, 1981, p. 63; Viles, 1995; Uroz et al., 2009). In one of the first compilations of the weathering literature, E. Yatsu (1988, p. 285-399) highlighted that eighteen percent of the references dealt with biological weathering. A particular concentration of research has focused on iron-oxidising bacteria and sulphur-oxidising bacteria related to pyrite weathering. Bacterial weathering is a micrometer-scale phenomenon. It therefore tends to be underestimated in the literature, compared to physical weathering and chemical weathering. The long geological history and ubiquitousness of bacteria warrant additional research on the weathering effects of bacteria. Bacteria are ubiquitous in soils, sediments, and subsurface environments with concentrations ranging from 105 cells/cm3 to 109 cells/cm3 (Hicks and Fredrickson, 1989; Kampfer et al., 1991; Albrechtsen and Winding, 1992; Edwards et al., 1998). Bacteria exist even in extreme environments, such as boiling hot spring or deep ocean sediments (Bland and Rolls, 1998; Ingraham and Ingraham, 2000; Madigan et al., 2003).
2The assumption of this research is that ubiquitous bacteria must have affected rock weathering to some extent, given their ubiquitous presence in the terrestrial weathering environment. General methods for weathering studies include field observation and experimentation. The need for microscopy to observe micrometer-scale bacteria leads us to understake an experimental approach. Experiments involving bacterial weathering are typically laboratory based (e.g., Vandevivere et al., 1994; Fein et al., 1999; Maurice et al., 2001), or field based (e.g., Bennett et al., 1996; Rogers and Bennett, 2004). Laboratory experiments have the advantage of being able to control conditions. Laboratory experiments usually consist of a medium (liquid), bacteria and minerals. Thus, laboratory experiments analyse the interaction of water, microorganisms, and mineral surfaces. Most of previous experiments used powdered or small fragmented minerals and only showed SEM images that were taken after the experiment (Paciorek et al., 1981; Escobar et al., 1996; Kalinowski et al., 2000). Comparison of rock or mineral surface images taken before and after an experiment are important to create a more thorough understanding of entire process of bacterial weathering. In addition, many of these previous studies have been mainly concerned with a single mineral and bacteria interactions (Lee and Fein, 2000; Edwards and Rutenberg, 2001; Yu et al., 2001, Cruz et al., 2005). Few bacterial weathering studies have analysed a suite of minerals that compose a rock (Vuorinen et al., 1981; Puente et al., 2006). An experiment using a rock composed of several minerals combined with SEM images comparison and chemical analysis of media, can show selective weathering of composing minerals in the rock.
3Our previous study (Song et al., 2007) on bacterial granite weathering has focused only on an experiment using granite. In this paper, we consider albite, microcline, and quartz and also upgraded experimental methods to enable quantitative surface analysis. The purpose of this work is to investigate (i) how the ubiquitous soil bacterium Bacillus subtilis weathers granite and its constituent single minerals through image analysis of mineral surface and (ii) which mineral in granite that appears to be the most vulnerable to bacterial weathering by Bacillus subtilis.
4Granite. Tab. 1 shows sampling point, normalised chemical composition, and bulk density of the specimens. Granite sampling point and preparation methods were same as that of Song et al. (2007). Ten test samples of granite were prepared (five for bacteria-bearing experiment and five for bacteria-free), 10.0 mm long, 10.0 mm wide, and 3.0 mm thick (fig. 1). The initial condition of the representative granite surfaces were coated with gold then observed with the aid SEM (Jeol, JSM-5600LV), prior to the start of the experiment. The images were acquired at 70 × magnification. It is a twice higher magnification than that of W. Song et al. (2007). The number 1 specimen (Gr1) was used for the bacteria-free experiment and the number 2 specimen (Gr2) was used in the bacteria-bearing experiment. The half of each granite surface (10.0 mm by 5.0 mm, yellow colored area in fig. 1) was analysed by SEM-EDS with 70 × magnification for chemical composition. Major element maps were obtained to approximate mineral distribution map with the SEM-EDS (Jeol, JSM-5600LV) overlay function. Fig. 1 shows the mineral distributions of the granite. Mineral area is calculated by using Adobe® Photoshop® 7.0.1 based on the overlaid element maps: plagioclase (Na-rich) 45-49%, quartz 28-35%, alkali feldspar 11-17%, and biotite 7-8%. Granite specimens were autoclaved at 121°C for 20 mn and dried in a desiccator for 1 h.
Fig. 1 –Mineral distribution of Gr1 and Gr2 analysed by SEM-EDS.
Fig. 1 – Distribution des minéraux dans les échantillons de granite (Gr1 et Gr2) analysés au MEB et à la micro-sonde.
10.0 × 5.0 mm area (yellow colored area) was analysed (Gr: granite). 1: quartz; 2: plagioclase; 3: K-feldspar; 4: biotite.
La zone colorée en jaune (10 x 5 mm) a été analysée (Gr : granite). 1 : quartz ; 2 : plagioclase ; 3 : feldspath alcalin ; 4 : biotite.
5Mineral preparation. Sampling points and bulk density for each mineral are shown in the tab. 1. Ten pieces of each mineral sample were prepared in a fashion similar to the granite rock fragments. However, only two samples from each mineral are a part of this experiment, one being subject to bacterial weathering (e.g., Ab2, Mc2, and Qtz2 in tab. 1). The other mineral is a control (e.g., Ab1, Mc1, and Qtz1 in tab. 1). SEM-EDS analyses of these minerals, normalised to 100%, are reported in tab. 1.
Tab. 1 – Sampling point, bulk density and chemical composition of the specimens.
Tab. 1 – Lieux d’échantillonnage, densité globale et composition chimique des échantillons.
|
Granite
|
Albite
|
Microcline
|
Quartz
|
Sampling point
|
Aji, Kagawa, Japan
|
Itoigawa, Niigata, Japan
|
Nellore, Andhra Pradesh, India
|
Minas Gerais, Brazil
|
|
Gr1
|
Gr2
|
Ab1
|
Ab2
|
Mc1
|
Mc2
|
Qtz1
|
Qtz2
|
Na2O
|
6.0
|
7.2
|
14.1
|
14.5
|
6.2
|
6.5
|
0.4
|
0.3
|
MgO
|
0.6
|
0.7
|
0.3
|
0.4
|
0.1
|
0.2
|
0.4
|
0.2
|
Al2O3
|
19.4
|
16,0
|
15.3
|
18.5
|
20.7
|
20,0
|
4,0
|
3.1
|
SiO2
|
67.4
|
70.4
|
69.6
|
66.1
|
63.6
|
63.9
|
94.8
|
96,0
|
K2O
|
2.9
|
1.5
|
0.1
|
0,0
|
9.2
|
9.1
|
0,0
|
0,0
|
CaO
|
1.7
|
2.1
|
0.3
|
0.3
|
0.1
|
0.1
|
0,0
|
0.1
|
TiO2
|
0.2
|
0.2
|
0.1
|
0,0
|
0,0
|
0.1
|
0.1
|
0,0
|
MnO
|
0.1
|
0.1
|
0.1
|
0,0
|
0.1
|
0.1
|
0.1
|
0,0
|
FeO
|
1.6
|
1.7
|
0.2
|
0.1
|
0.1
|
0.1
|
0.1
|
0.2
|
Total
|
100,0
|
100,0
|
100,0
|
100,0
|
100,0
|
100,0
|
100,0
|
100,0
|
Bulk density (in g/cm³)
|
2.67
|
2.67
|
2.6
|
2.6
|
2.57
|
2.57
|
2.63
|
2.63
|
* Chemical composition was measured by using SEM-EDS. The values of the chemical composition are normalised.
* La composition chimique a été analysée à la micro-sonde (MEB). Les valeurs sont normalisées.
6Bacteria and medium. This experiment used the same species of bacteria (Bacillus subtilis strain 168) as W. Song et al. (2007). Bacillus subtilis is a gram-positive, aerobic bacterium that is commonly found in soil, groundwater, plants, air, and hay. These bacteria are shaped like a rice grain, with a width of 0.7-0.8 µm and a length of 1.5-2.0 µm. Bacillus subtilis was grown on the polypepton (Wako 394-00115) agar plate. Composition of the medium is shown in tab. 2. The medium (total volume of a each bottle is 500 ml) for the incubation of the strain 168 consisted of 0.1 M NaCl, 0.4% (w/v) glucose, and 0.1% (w/v) yeast extract (Difco 212750, Bacto TM Yeast Extract, Extract of Autolysed yeast cells). A more detailed explanation of the medium is described in W. Song et al. (2007). The net weight of bacteria is 8-10 mg per a bottle.
Tab. 2 – Composition of the medium.
Tab. 2 – Composition du médium expérimental.
Sample name
|
Medium (in ml)
|
Innoculation (in mg)
|
Glucose (wt. in %)
|
Yeast extract (wt. in %)
|
Gr1
|
500
|
None
|
0.4
|
0.1
|
Gr2
|
500
|
10
|
0.4
|
0.1
|
Ab1
|
500
|
None
|
0.4
|
0.1
|
Ab2
|
500
|
8
|
0.4
|
0.1
|
Mc1
|
500
|
None
|
0.4
|
0.1
|
Mc2
|
500
|
8
|
0.4
|
0.1
|
Qtz1
|
500
|
None
|
0.4
|
0.1
|
Qtz2
|
500
|
8
|
0.4
|
0.1
|
Ctrl1
|
500
|
None
|
0.4
|
0.1
|
Ctrl2
|
500
|
8
|
0.4
|
0.1
|
7Experimental methods. The experimental setup is shown in fig. 2. Two holes in the silicone packing of the bottles were for input air by an air pump and for output. The air pump supplied air (500 cc/min) to the all bottles. The bottles were placed in an incubation room at 27°C. After 30 days, granite and mineral specimens were taken out of the bottle with autoclaved forceps, washed lightly with ultra-pure deionised water (milliQ), and dried at room temperature for a few days. The surfaces of the specimens were then observed by SEM to compare with images acquired before the experiment. Images were examined on the computer screen and on hardcopy (transparent films). Newly formed pits were counted manually. Defects and pits greater than a width of 5 µm can be identified at 70 × magnification. Thus, our methodology is to systematically ignore weathering pits less than 5 µm.
Fig. 2 –Contour of the experiment.
Fig. 2 – Aspect du protocole expérimental.
Red circled granite and minerals are representatively observed before and after the experiment (Gr: granite; Ctrl: control; Ab: albite; Qtz: quartz; Mc: microcline).
Les échantillons de granite et les minéraux cerclés de rouge ont été observé avant et après l’expérimentation (Gr : granite ; Ctrl : contrôle ; Ab : albite ; Qtz : quartz ; Mc : microcline).
8Granite (bacteria-free/bearing). After 30 days, pits were found on surfaces of both bacteria-bearing granite (Gr2) and bacteria-free granite (Gr1). However, the number, size and distribution of pits were very different in these two samples (Gr1 and Gr2). Comparing magnified images of a part of bacteria-free (Gr1) before and after the experiment, for example, reveals that the surface of plagioclase did not change substantially after the 30-day experiment (fig. 3).
Fig. 3 –Comparison of the Gr1 surface before and after the experiment
Fig. 3 – Comparaison de la surface de l’échantillon Gr1 avant et après l’expérimentation
(Pl: plagioclase; K-fs: alkali feldspar; Bt: biotite). Plagioclase did not change substantially after the 30-day experiment.
(Pl : plagioclase ; K-fs : feldspath alcalin ; Bt : biotite). Le plagioclase n’a subi aucune modification notable au terme des 30 jours d’expérimentation.
9In contrast, many pits were formed on a similar plagioclase surface for the bacterial-bearing sample (Gr2) (fig. 4). The SEM images of Gr2 after the experiment also shows many angular pits with bacteria (cocoon shaped materials with ca. 1 µm length). To assess the difference between Gr1 and Gr2 quantitatively, the total number and size of pits were compared. A different SEM using secondary electrons (Keyence, VE-9800) and Adobe® Photoshop® 7.0.1 were used in the calculation of pit area. Concerning the number and size of pits, tab. 3 summarises measured data on micrometer-scale pitting, both number and area. Tab. 3 includes specifies for each different mineral in the granite (Gr1 and Gr2). In the bacteria-free granite (Gr1), 52 of new and widened pits were found on the surface that is 10.0 mm long and 5.0 wide (tab. 3A). Twenty-one pits (40% of the pits) were observed in plagioclase, 9 in quartz (17% of the pits), 5 in biotite, and one pit was found in alkali feldspar. Nine pits were found on the grain boundaries between quartz and plagioclase. The total area of the newly formed pits on the Gr1, calculated by SEM (Keyence, VE-9800), is approximately 3573 µm2. Frequency distribution of pit area of the Gr1 is shown in fig. 5. Pit area which is under 100 µm2 is the largest, and among the pits plagioclase dominates over 20%. In bacteria-bearing granite (Gr2), 192 of new and widened pits were found after the experiment (tab. 3B). Among these pits, 137 pits were formed in plagioclase (71% of the pits), 9 in quartz (5% of the pits), and 13 in biotite (7% of the pits). Seven pits were found in alkali feldspar and 22 at the boundary of plagioclase and quartz (11% of the pits). Over 70% of the pits were formed in plagioclase. The total area of the pits is 16735 µm2. Frequency distribution of pit area of the Gr2 is wider than Gr1, however most of the pit area are under 100 µm2 (fig. 5). The number of pits Gr2 was 3.7 times as large as that on Gr1. The total area of pits on the bacterially weathered Gr2 was 4.7-times larger than that on the bacteria-free Gr1.
Fig. 4 – Comparison of the Gr2 surface before and after the experiment
Fig. 4 – Comparaison de la surface de l’échantillon Gr2 avant et après l’expérimentation
Pl: plagioclase; Bt: biotite; Qtz: quartz
(Pl : plagioclase ; Bt : biotite ; Qtz : quartz)
Tab. 3 – Number, area and volume of the newly formed or widened pits, in Gr1 and Gr2.
Tab. 3 – Nombre, surface et volume des puits néoformés ou agrandis dans les échantillons Gr1 et Gr2.
(A) Gr1 (bacteria-free)
|
|
|
|
Pit number
|
Pit number ratio (in %)
|
Av. Area (in μm2)
|
Total pit area (in μm2)
|
Pl
|
21
|
40
|
88
|
1848.5
|
Qtz
|
9
|
17
|
53.9
|
484.8
|
Kfs
|
1
|
2
|
22.7
|
22.7
|
Bt
|
5
|
10
|
59.7
|
298.5
|
Pl-Kfs
|
2
|
4
|
99
|
197.9
|
Pl-Bt
|
0
|
0
|
0
|
0
|
Qtz-Pl
|
9
|
17
|
36
|
323.6
|
Qtz-Kfs
|
3
|
6
|
46.2
|
138.7
|
Qtz-Bt
|
1
|
2
|
174
|
174
|
Qtz-Pl-Kfs
|
1
|
2
|
83.9
|
83.9
|
Qtz-Pl-Bt
|
0
|
0
|
0
|
0
|
Total
|
52
|
100
|
|
3572.8
|
|
|
|
|
|
(B) Gr2 (bacteria-bearing)
|
|
|
|
Pit number
|
Pit number ratio (in %)
|
Av. Area (in μm2)
|
Total pit area (in μm2)
|
Pl
|
137
|
71
|
97.6
|
13376.1
|
Qtz
|
9
|
5
|
43.5
|
391.6
|
Kfs
|
7
|
4
|
106.8
|
747.8
|
Bt
|
13
|
7
|
76.6
|
995.3
|
Pl-Kfs
|
0
|
0
|
0
|
0
|
Pl-Bt
|
1
|
1
|
82.2
|
82.2
|
Qtz-Pl
|
22
|
11
|
43.4
|
955.9
|
Qtz-Kfs
|
2
|
1
|
46.7
|
93.5
|
Qtz-Bt
|
0
|
0
|
0
|
0
|
Qtz-Pl-Kfs
|
0
|
0
|
0
|
0
|
Qtz-Pl-Bt
|
1
|
1
|
92.3
|
92.3
|
Total
|
192
|
100
|
|
16734.7
|
Fig. 5 – Frequency distribution of pit area of the granites. Fig. 5 – Fréquence des puits observés sur les granites, classés selon leur taille.
1: other mineralspits formed in Qtz, Kfs, Bt, and mineral boundaries;2: plagioclase: pits formed in plagioclase.
1 : autres minéraux : puits formés dans le quartz (Qtz), les feldspaths alcalins (Kfs), la biotite (Bt) et aux frontières inter-minérales ; 2 : plagioclases : puits formés dans les plagioclases.
10Albite (bacteria-free/bearing). In bacteria-free specimen (Ab1), 19 pits were found after the experiment (tab. 4). Fifty-two new pits were found in the bacterially-weathered Ab2. Fig. 6 shows SEM image, both before and after, of Ab1 and Ab2. Arrows show newly formed pits after the experiment. However, bacteria were rarely seen on the mineral surfaces.
11Microcline (bacteria-free/bearing). Two pits were found in the bacteria-free specimen, Mc1 (tab. 4). The upper two images in fig. 6 show the surface of Mc1 before and after the experiment. Nothing has changed after the experiment. Most surface of the Mc1 was similar to the magnified images of fig. 7. Four pits were found in the bacterially-weathered Mc2. Fewer bacteria are seen on the surface of Mc2 compared to a similar surface area of the bacterially weathered granitic slab, Gr2. The lower two images in fig. 7 show the surface of Mc2 both before and after the experiment. With a magnification of 70 ×, micro-meter-scale materials were observed on the surface of Mc2.
Tab. 4 – Number of the newly formed pits.
Tab. 4 – Nombre de puits néoformés.
Number of the pits
|
Gr
|
Ab
|
Mc
|
Qtz
|
Bac-free
|
52
|
19
|
2
|
0
|
Bac-bearing
|
192
|
52
|
4
|
0
|
Fig. 6 –SEM Image comparison of Ab1 (upper, bacteria-free), and Ab2 (lower, bacteria-bearing).
Fig. 6 – Comparaison d’images MEB des échantillons d’albite : Ab1 (en haut, protocole sans bactérie), Ab2 (en bas, protocole bactérien).
Arrows show newly formed pits after the experiment.
Les flèches signalent les puits apparus durant l’expérimentation.
Fig. 7 – SEM image comparison of Mc1 (upper, bacteria-free), and Mc2 (lower, bacteria-bearing).
Fig. 7 – Comparaison d’images MEB des échantillons de microcline : Mc1 (en haut, protocole sans bactérie), Mc2 (en bas, protocole bactérien).
12Quartz (bacteria-free/bearing). No pits were found in either bacteria-free or bacteria-bearing specimens (Qtz1, and Qtz2; tab. 4). The upper two images in fig. 8 show the surface of Qtz1, before and after the experiment. Nothing has changed after the experiment. The lower two images in fig. 8 show the surface of bacteria-bearing quartz (Qtz2). Again, we could detect no changes after the experiment except for a few bacteria present on the surface of Qtz2.
Fig. 8 – SEM image comparison of Qtz1 (upper, bacteria-free), and Qtz2 (lower, bacteria-bearing).
Fig. 8 – Comparaison d’images MEB des échantillons de quartz : Qtz1 (en haut, protocole sans bactérie), Qtz2 (en bas, protocole bactérien).
13An overall picture of the influence of bacteria on weathering a 10 mm by 5 mm slab of granite can be obtained in tab. 5. To construct tab. 5, the area of all pits on a mineral boundary was equally divided by the number of minerals and added to the each mineral area. The plagioclase occupies nearly half area (49% of Gr1, 45% of Gr2) of both granite specimens. Since areal ratio of each mineral is different, normalisation of the pit area provides more insight. Normalised pit-area ratio is calculated here as; normalised pit-area ratio (%) = total pit area (µm2) / mineral area (µm2). We also employed another parameter, pit density, that is defined as the number of pit per unit area, i.e., pit density (mm-2) = the number of pits / mineral area (mm-2). The results for granite specimens (Gr 1 and Gr2) are shown in tab. 6. The order of the both normalised pit-area ratio and pit density of minerals in the bacteria-bearing specimen (Gr2) is: plagioclase > biotite > alkali feldspar > quartz. Plagioclase has the highest normalised pit-area ratio or pit density in Gr2. Pit density of plagioclase (6.619 mm-2) is over 5.5 times higher than that of quartz (1.205 mm-2) in Gr2 (tab. 6). In contrast, the order of the normalised pit-area ratio of minerals in bacteria-free specimen (Gr1) is: biotite > plagioclase > quartz > alkali feldspar. The order of the pit density of minerals in Gr1 is: biotite > quartz > plagioclase > alkali feldspar. Plagioclase has the largest total pit area in each bacteria-free and bacteria-bearing condition (tab. 3). However, when it is arranged in the order of normalised pit ratio, biotite has the largest pit area ratio and pit density for bacteria-free granite (tab. 6). Plagioclase, thus, appears to be the most vulnerable to Bacillus subtilis in Gr2. This effect is also seen in the single mineral experiment where albite (plagioclase group) has the most pits after the experiment in bacteria-bearing circumstances (fig 4, lower images). The order of normalised pit-area ratio and pit density in bacteria-bearing granite are in accorded with the traditional weathering-series of S.S. Goldich (1938): plagioclase > biotite > alkali feldspar > quartz. Similar results are found in the single mineral experiments: albite > microcline > quartz.
14W.W. Barker et al. (1997) reported that feldspars are more susceptible to microbial attack than quartz because they contain ions that react strongly with microbially produced compounds, such as organic acids. When ample organic acids derived from bacteria, algae, fungi and lichens are present, the weathering sequence matches the Goldich model (Bland and Rolls, 1998). It suggests most of the early work on weathering sequences relied on data from samples taken from environments. The Goldich’s classic sequence of mineral susceptibility to weathering may vary with the nature of the biochemical environment (Wasklewicz, 1994). On the other hand, the weathering sequence for bacteria-free granite of the present research is different from the Goldich’s sequence, perhaps because of the lack of biological activity. The accordance of the bacterially-weathered with Goldich’s weathering sequence suggests that Goldich did not simply study chemical weathering. Goldich’s observations must have mixed purely chemical and biochemical reactions in his field sites.
Tab. 5 – Mineral area ratio and total pit area of the granite.
Tab. 5 – Proportion des différents minéraux et surface des puits dans le granite.
|
Gr1 (bacteria-free)
|
Gr2 (bacteria-bearing)
|
|
Mineral area ratio (in %)
|
Total pit area (in μm2)
|
Mineral area ratio (in %)
|
Total pit area (in μm2)
|
Pl
|
49,0
|
2137.3
|
45,0
|
13925.9
|
Qtz
|
27.7
|
831,0
|
35.4
|
947.1
|
Kfs
|
16.6
|
219,0
|
11.2
|
794.5
|
Bt
|
6.7
|
385.5
|
8.4
|
1067.1
|
Total
|
100,0
|
3572.8
|
100,0
|
16734.7
|
Tab. 6 – Normalised pit-area ratio and pit density for bacteria-free (Gr1) and bacteria-bearing granite (Gr2).
Tab. 6 – Proportion normalisée des surfaces de puits et densité de puits sur les granites pour les protocoles sans bactérie (Gr1) et bactérien (Gr2).
|
Normalised pit area ratio (in %)
|
pit density (in mm-2)
|
|
Gr1
|
Gr2
|
Gr1
|
Gr2
|
Pl
|
0.0087
|
0.0619
|
1.095
|
6.619
|
Qtz
|
0.006
|
0.0054
|
1.143
|
1.205
|
Kfs
|
0.0026
|
0.0142
|
0.462
|
1.427
|
Bt
|
0.0115
|
0.0254
|
1.642
|
3.29
|
Whole analysed area
|
0.0289
|
0.1068
|
1.04
|
3.84
|
15The present research reveals that bacteria can play an important role in weathering of granite and its constituent minerals by making pits. Our quantitative analyses reveal that the area of the newly formed pits on the bacteria-bearing granite surface is 4.7 times larger than bacteria-free granite. Plagioclase or albite (plagioclase group) appears the most vulnerable mineral to weathering by Bacillus subtilis. The weathering sequences obtained in the present research are in accorded with the traditional Goldich’s weathering-series. Thus, we speculate that this classic weathering sequence is not just chemical weathering, but should be interpreted as a mixture of chemical and biochemical weathering.