A STUDY OF CLAY MINERALS IN PODZOL SOILS IN NEW BRUNSWICK, EASTERN CANADA

Transcription

1 Clay Minerals (1968) 7, 295. A STUDY OF CLAY MINERALS IN PODZOL SOILS IN NEW BRUNSWICK, EASTERN CANADA H. KODAMA AND J. E. BRYDON Soil Research Institute, Department o/ Agriculture, Ottawa, Ontario, Canada (Received 26 September 1967) ABSTRACT: Clays from the Ae and C horizons of five Podzol soil series in New Brunswick were examined by X-ray, chemical and infrared absorption methods. ALl the experimental evidence indicated that the Ae horizons contained predominantly a dioctahedral randomly interstrafified mica-vermiculite--smectlte clay, whereas the C horizons contained abundant dioctahedral mica (illite) and trioctahedral chlorite. Since no trace of chlorite as a separate phase or as one component of the interstratified structure was found in the Ae horizons, it was concluded that, while the inherited chlorite was decomposed in all of the Ae horizons, mica was differentially hydrated giving an interstratified structure. Fourier transforms of the three-component interstratified clay revealed different ratios of hydrated layers (vermiculite and smectite) to non-hydrated layers and different stacking sequences. The proportion of hydrated layers and randomness of stacking was related to the degree of weathering as measured by the accumulation of TiO 2 in the Ae horizon and it was suggested that they may be related to the degree of podzolization. INTRODUCTION Mineralogical studies on soils in eastern Canada have shown that in general illite is the predominant clay mineral with chlorite and vermiculite present in lesser amounts (Forman & Brydon, 1961). In the course of investigating Podzol soils from New Brunswick, it was found that illite and chlorite were abundant in C horizons, that chlorite had disappeared from the Ae horizon and that a smectite-like interstratified clay was a major component mineral in Ae horizons (of. Brydon, Kodama & Ross, 1968). It was thought that a more detailed study of the clay minerals would elucidate the weathering mechanisms which seemed to prevail on the basis of the above data. EXPERIMENTAL Materials and sample preparation METHOD Samples were collected from the Ae and C horizons of each of five Podzol soil

2 296 H. Kodama and J. E. Brydon series in New Brunswick.* A summary of the soil samples, their parent materials and underlying bedrock is given in Table 1. Portions of the air-dried, less than 2 mm samples were titrated to ph 3"5 with 1 N HC1 to remove carbonates and treated with H202 to destroy organic matter. After washing the samples with water, they were fractionated by a combination of sedimentation and centrifugation into three fractions: fine silt (5-2 t~), coarse clay (2-0-2 ~) and fine clay (<0"2 t~). The samples were concentrated by flocculation with acidified CaC12 solution, then washed free of chloride with water and ethyl alcohol and freeze-dried. TABLE 1. Description of the soil samples Sample Soil Sample Underlying No. Horizon series location rock Remarks SMJ 1 Ae Kedgewick Near Kedgewick Limestone, Bisequa Podzol developed 47 ~ 40' 67 ~ 23' shale on an ablation moraine SMJ 2 C Restigouche Co. (Ordovician) SMJ 1 (Ae) is from the upper A horizon* SMJ 3 Ae Monquart SMJ 4 C Near Carlingford Quartzite, An Orthic Podzol devel- 46 ~ 46' 67 ~ 46' argiuite, oped on an ablation Victoria Co. shale moraine ~" SMJ 5 SMJ 6 Ae C Glazier Baker Brooke Shale An Orthic Podzol formed 47 ~ 18' 68 ~ 35' argillite, on water deposited Madawaska Co. phyllite materials* SMJ 7 SMJ 8 Ae C Serpentine Lorne Parish Argillite, 47 ~ 05' 67 ~ 00' quartizite Victoria Co. schist, some volcanics (Ordovician) An Orthic Podzol formed on an ablation moraine* SMJ 9 Ae 47 ~ 00' 67 ~ 00' Granite, An Orthic Podzol formed Tuadook basalt, on a ground moraine* SMJ 10 C rhyolite *Langmaid (1967). ~Millette & Langmaid (1963). Analytical techniques X-ray analysis was carried out with a Philips diffractometer using Fe-filtered Co-radiation (Co Ka. X= 1"7902 A) on non-oriented and oriented specimens. The oriented specimens were prepared by allowing 1 ml of the suspension containing 20 mg of sample to settle and dry on a 37"5 mmx 25 mm glass slide. Clay minerals were identified by interpretations from X-ray experimental results on the oriented * From K. K. Langmaid, Fredericton, N.B.

3 Clay minerals in Podzol soils 297 specimens under various conditions included glycerolation, heating, extremely dry (<3% relative humidity) and humid (95% relative humidity) conditions. In some phases of the investigation, X-ray diffraction patterns were recorded while the specimens were maintained at approximately 100 ~ C to characterize the hydrated phyllosilicate layers. Since it is difficult to identify kaolinite in the presence of chlorite by X-ray examination an infrared absorption technique was used (Kodama & Oinuma, 1963). The absorption spectra were obtained with a Beckman IR 12 infrared spectrophotometer using samples prepared as a mull in Nujol and mounted between NaC1 plates. Chemical analysis was performed using the X-ray spectrochemical method developed by Kodama, Brydon & Stone (1967). Free iron oxide analysis was made by the method described by Mehra & Jackson (1960). After treatment, extractable AI was determined colorimetrically (Robertson, 1950). Diagnostic criteria ]or clay minerals 10.4 clay mica (illite). A 10 A basal spacing and its integral series of higher order reflections (00l) do not shift upon either solvation with glycerol or heating at 550 ~ C. Some information about its chemical structure is provided by the position of the 060 reflection and the intensity ratio 1(001)/1(002) (Brown, 1955). Chlorite. An integral series of peaks associated with the largest basal spacing of 14 A does not expand by glycerol sorption and does not shift upon heating at 550 ~ C. The intensity ratio of the basal reflections may be used to define a species of chlorite minerals (Brindley & GiUery, 1956). Vermiculite and smectite. Neither of these minerals was present as an independent mineral constituent of soils in the present study, but structures equivalent to those of both minerals occurred as components in various types of interstratifications. Although those layers may not be identical with typical vermiculite or smectite, it is useful to distinguish them conventionally on the following basis: vermiculite maintains its 14 A basal spacing upon solvation with glycerol and under high relative humidity, whereas smectite (Ca-form) exhibits an expansion of its basal spacing (15 A at room relative humidity % R.H.) to about 18 A under high humidity or glycerolation. Both of them collapse to 10 A upon heating to 550 ~ C, which is obviously different from chlorite which remains unchanged at that tempperature. Interstratified minerals. There were several types of interstratified minerals in these clays. Most of them showed an intermediate d-spacing indicating a hybrid nature with no long-spacing periodicity. They consisted of two or three component layers of mica-, vermiculite-, chlorite- and smectite-like layers. The determination of types of interstratifications was based on a combination of the characteristics of each component-layer that was mentioned in preceding sections. Brief criteria are tabulated in Table 2. Interstratified mixtures of the three components, micavermiculite-smectite were the only predominant and the most significant materials. Their detailed analyses are described in a later section of this paper.

4 298 H. Kodama and J. E. Brydon T,~Lr~ 2. Criteria used for determination of types of non-regular interstratifications indicated by the first-order basal spacing (A) following different treatments Type of Glycerol Humid Air-dry Very dry 110 ~ C 550 ~ C interstratification* 95 % RH 45 % RH 3 % RH Mica-vermiculite 1 I " "5 10 Mica-chlorite 1" I I 1" Mica-smectite 10or 18 Expansion 10-15' ' "5 10 Vermiculite--chlorite 1 I" " " Vermiculite--smectite Expansion Chlorite--smectite Expansion 14-15" Mica-vermiculite--chlorite I" i Contraction Contraction Mica-vermiculite--smectite Expansion Expansion 10-15"4 Contraction Contraction 10 Vermiculite-chloritesmectite Expansion Expansion Contraction Contraction Expansion and contraction mean shift of the original first-order reflection (air dry) towards large and small spacing sides respectively. * As Ca-saturated specimen. Indicates that the basal spacing is unchanged from air-dry. Kaolinite. In the present study, kaolinite was only a minor constituent of the clays. Because of its association with chlorite in most cases, the infrared absorption technique was applied. Kaolinite can be identified by the presence of an absorption peak at 3700 cm -1 in the absence of brucite (Oinuma & Kodama, 1967) and is detectable down to a few per cent of total clay (Kodama & Oinuma, 1963). Mica and chlorite RESULTS AND DISCUSSION Both of these minerals were present abundantly in C horizons. The micas were aluminous and of a dioctahedral-type, since the intensity ratios 1(001)/1(002) were less than 4 and 060 reflections appeared at 1"50 A. The chlorite minerals showed that their odd order reflections were weaker than the even order reflections. The ratios 1(002)/1(001) of the chlorites were between 3 and 4, which indicated that they were of a trioctahedral-type. A further confirmation was made by the evidence that the ratios 1(003)/1(002) were less than 1, since a dioctahedral chlorite should have the intensity ratio of more than 1"5 (Hayashi & Oinuma, 1964; Eggleston & Bailey, 1967). lnterstratified mica-vermiculite-smectite clays The three-component interstratified clays were abundant in the three fractions of the Ae horizons of all soils. They showed a large broad peak with single or double maxima ranging between 11 and 13-5 A at room temperature and 45% R.H. Generally the magnitude of the spacing depended upon the size fraction, that is,

5 Clay minerals in Podzol soils 299 the larger spacing appeared in the finer fraction. Upon solvation with glycerol, the broad peak was split into fairly well defined peaks which were shifted to larger spacings. The spacings of the shifted peaks were either one of 12, 13"8 and 17"6 A depending on the position of the original spacing. In addition to this, a separate peak appeared in most cases at approximately 10 A. Similar results were obtained from Ca-saturated samples after removal of free iron by the dithionite--citrate treatment, excepting that the treatment caused a slightly larger spacing in both the air-dry and glycerolated specimens. When the untreated air-dry samples were heated to 550 ~ C, the large broad peak collapsed completely to 10 A. Powder patterns of the nonoriented specimens showed the presence of a reflection at 1"50 A. This behaviour indicated that the interstratified clays contained mica-like and smectite-like layers but not chlorite-like layers. However, the basal peak positions of glycerolated samples could not be interpreted from the published data on twocomponent mica-smectite interstratification (MacEwan, Ruiz & Brown, 1961; 3-3 3"5 4 d-spacing (~) 5 6 "7 8 9 I0 14 I8 (a) (b) Co) (d) (e) t5 lo 5 Degrees, 28 CoKc~ FiG. 1. X-ray diffraction patterns of oriented specimen of the minus 0.2/~ fraction from sample SMJ 1. (a) is untreated air-dry specimen; (b) is glycerol-saturated specimen; (c) is the specimen under 95 % relative humidity condition; (d) is the specimen kept at I I0 ~ C; (e) is the specimen after heating at 550~

6 300 H. Kodama and J. E. Brydon d- spocing (~) 3"53' IO I418 (o) J (b)! - lj (c) (e) 35!,, I,,I I, t, I0 5 Degrees, 28 CoKa J J FIG. 2. X-ray diffraction patterns of oriented specimen of the minus 0'2 t~ fraction from sample SMJ 9. (a) is untreated air-dry specimen; (b) is glycerol-saturated specimen ; (c) is the specimen under 95 % relative humidity condition; (d) is the specimen kept at 110 ~ C; (e) is the specimen after heating at 550 ~ C. Cesari, Morelli & Favretto, 1965; Reynolds, 1967). This suggested that the material consisted of a multi-component interstratification and that the direct method of MacEwan (1956) could be used to interpret the X-ray diffraction data. For this purpose the minus 0'2 t~ size fractions were most suitable, because of a high concentration of the interstratified clays. Among the five samples from the Ae horizons, SMJ 1 and SMJ 9 seemed to exhibit extremes of behaviour on the basis of the X-ray diffraction data (Figs 1 and 2). The same relation was also observed in the coarser fractions. The first-order basal reflection of-smj 1 appeared at 12"5 A in the air-dry condition and moved to 13-3 A upon glycerolation whereas that of SMJ 9 appeared at 13"3 A in the air-dry condition and the reflection was split into two peaks at 13.8 and 17.6 A after glycerol-sorption. The other samples showed characteristics intermediate between the above two. Therefore the Fourier transform analyses were made on the two samples using air-dry specimens.

7 Clay minerals in Podzol soils 301 Basal reflection data were obtained using oriented specimens under varying conditions of slit widths and scale factors in order to record each basal reflection adequately. The peak area was measured by means of a planimeter and expressed in arbitrary units. Peak areas for the various operational conditions were compared on the basis of the 1 ~ slit and the x c/min scale factor with which the diffraction pattern for SMJ 1 was taken. The compiled intensity data are listed in Table 3 with the record of diffraction angles and d-spacings. After the correction TABLE 3. X-ray diffraction data (air-dry) for the minus 0-2/~ size fraction samples ofsmj 1 and SMJ 9 at room temperature and 40-50% RH 20 (deg.) d(a) I (arbitrary units) SMJ 1 8"2 12" "7 4" '3 3" " "2 1 " SMJ 9 7"7 13" "7 4' '2 3" "7 2" " for Lorentz-polarization factors, the integrated intensities were converted to Fourier coefficients using conventional layer structure factors published by Cole & Lancucki (1966) for hydrous dioctahedral mica type layers. In the absence of definite chemical formulae of the interstratified components, no absorption correction was made. In order to check the effect of absorption on the intensity data, using a hypothetical composition and the sample thickness of cm, the absorption correction was calculated. The correction increased the intensity of the highest order reflection by about 20%. In the present case, however, because intensities of the higher orders were very weak, the revised values of Pa, PB and Pe did not differ by more than 2%. The Fourier transforms (Fig. 3) were calculated by means of an IBM 1620 computer. Both of the transforms showed three fundamental components with spacings of 10(A), 13-6 (B) and 15.8(C) A. Since chlorite had been found to be absent, the three fundamental components were assigned to mica-like, vermiculite-like and smectite-like layers, respectively. A further support of the assignment may be given by the evidence that high humidity caused an expansion of the first-order reflection and that the extremely dry condition, which was obtained by maintaining the temperature at I10 ~ C, shifted the reflection towards a spacing between 10 and 11.5 A (Figs 1 and 2). Lists of assignments for peaks on the Fourier transforms are given in Table 4 with a comparison of the observed peak heights with the calculated ones.

8 302 H. Kodama and J. E. Brydon to < to < t m+ _~ ~ +: <% to,~ (a) r W (R) ~ u to +. (b),,,,,,,,i,...,,i... l,,,,,,,,,l,,... 0 I R (~) FIG. 3. Fourier transforms of basal reflections of untreated air-dry intcrstratified mica-vermiculite--smectite clays. (a) Sample SMJ 1; (b) sample SMJ 9. The comparison indicated a good agreement between the observed and calculated peak heights. The probability coefficients were then deduced from the observed data of peak heights and are listed in Table 5. The mixing ratios of the three components (mica-vermiculite-smectite) were 0-53:0"27:0"20 for sample SMJ 1 and 0.40:0.38:0-22 for sample SMJ 9, as obtained directly from probability coefficients for the three fundamental components. In sample SMJ 1, the mica layers had a tendency to pile together to produce a zonal structure [P, ta (0.74) > PX (0"53)], but not in sample SMJ 9 (PaA < P,t). Both Fourier transforms (Fig. 3) showed a prominent combination peak at 40 A consisting of contributions from both AAAA-type and ABC-type layer successions. The latter type of succession includes six orderings such as ABC, ACB, BAC, BCA, CAB and CBA. In sample SMJ 1, the calculated height ratio of the 40 A peak is 0-37, of which only two-fifths belongs

9 Clay minerals in Podzol soils 303 TABLE 4. Comparison of observed peak heights on Fourier transform with calculated peak heights for untreated samples of SMJ 1 and SMJ 9 SMJ 1 SM.I 9 Spacing Calculated Observed Spacing (A) Peak height height (A) Peak Calculated height Observed height " " " A A "40 B B C C AA AA AB AB AC "35 26"1 AC 0" AAA BC 0-29} 0"09 0"38 29"9 {AAA BC 0'05/ 0"30 J 0"37 AAB 0"2i 0"19 AAC "35 36"2 AAC 0" ABC AAAA 0"22 t 0-15 J 0"46 40"0 { AAAA ABC "37, 0"59 {AAAB BBC 0-19} 0" {AAAB BBC 0.04} 0"05 0"15 AAAC 0" [ AAAAA 0"16 / 0" { AAAAA 0.01} t AABC 0"19 J AABC 0"30 0"35 TABLE 5. Probability coefficients deducted from Fourier transforms of calcium saturated clays SMJ I and SMJ 9 SMJ 1 SMJ 9 PA --'~ 0"53 P~, = 0-40 Pa = 0.27 Ps = 0.38 Pc = 0.20 Pc = 0.22 PAA = 0"74 PAA = 0"35 PAB = 0"16 PAB = 0"10 PAC = 0"10 Pgc = 0"55 PBA = 0"74 PBA = 0"45 PBs = 0 Pss = 0 Psc = 0-26 PBc = 0"55 PeA "90 PCA = 0"77 PcB = 0"10 PcB = 0"23 Pcc = 0 Pet = 0 to the contribution from an ABC-type layer succession (Table 4). While, in the case of the sample SMP 9, the calculated height ratio of the corresponding peak is 0.39 almost all of which, 0"37, contributes to the probability that the ABC-type layer succession occurs (Table 4). It could, therefore, be concluded that the threecomponent layers of SMJ 9 were more randomly interstratified than those of SMJ 1.

10 304 H. Kodama and J. E. Brydon Mineral associations Table 6 summarizes the clay mineral assemblages in the soils with a semiquantitative estimation of each clay mineral. In the C horizons, the coexistence of mica with chlorite was characteristic. Chlorite tended to be less concentrated in the fine fraction and substituted by several types of interstratified clays in which TABLE 6. Clay mineral associations of the soils Interstratified clay minerals Soil type Hori- zon Fraction Chlorite Mica Kaolinite M--Ch V-Ch Ch-S M-V-S M-V-Ch Kedge- wick Ae 5-2/~ -- *.... ** 2-0.2/~ -- *.... *** <0.2/z -- **.... *** ~ ** ** * /~ * *** tr *.... < 0"2/~ -- *** tr * * Monquart Ae C 5-2 t~ -- **.... ** 2-0"2 ~ -- *.... *** < 0"2/,~ -- **.... *** 5-2 tz ** *** * '2/z * *** *.... * <0"2/~ -- *** tr.... ** Glasier Ae C 5-2/* -- **.... ** "2/~ -- *.... *** -- <0"2t* -- * tr *** /z *** ** '2 t~ ** ** <0'2~ * *** Serpen- fine Ae C 5-2 tz -- **.... ** tz -- * tr *** -- <0'2/~ -- * tr *** ~ ** ** * * /~ ** ** * -- * ** <0'2 p, -- *** * *** Tuadook Ae 5-2~ tr -- tr tr * - - i - - <0.2a -- tr C 5.2tz <0.2 tz *** Abundant M: Mica * * Moderate * Minor tr Trace V: Vermiculite Ch: Chlorite S: Smectite

11 Clay minerals in Podzol soils 305 chlorite was one component. This may suggest a gradual weathering of chlorite to its derivatives in the C horizons. In the Ae horizons, the interstratified micavermiculite-smectite clays were predominant whereas chlorite had disappeared completely. Mica was another component mineral in the Ae horizon but its quantity was moderate to trace. Kaolinite occurred occasionally as a small quantity in both Ae and C horizons. It occurred only as a trace in the Kedgewick C horizon and was present in minor amounts in the Monquart, Serpentine and Tuadook. There was a decrease in kaolinite content from the C to the Ae horizon of the Kedgewick, Monquart and Serpentine. These clay minerals were generally accompanied by quartz and feldspar, and their quantities decreased with decreasing size of fraction. Further information about the feldspar minerals was obtained by X-ray diffraction data for non-oriented and (111) reflection at 3"77 A. Assuming the absence of unmixing of peristerite-type powder samples of the 5-2 t~ fractions. Powder patterns of all five silt fractions gave a single (20[) reflection at 4"03 A and the separation of (1i1) reflection at 3"87 A according to Smith's diagram (1956), the measure 20 (111)-20 (1~ 1) of those samples corresponded to plagioclase with the composition in the region An2o-Ana0. Because of the assumption, the identification of the plagioclase species is inconclusive. A minor quantity of an amphibole mineral is present in the 5-2 /~ fraction of C horizons of Serpentine and Tuadook. Chemical composition The total chemical composition of the respective ~ samples only is reported in Table 7, because the composition of the 5-2 ~ fraction was affected by the primary minerals present and there was insutlicient material in some of the <0"2 t~ fractions for analysis. The difference in chemical composition (Table 7) between the Ae and C horizons supports the foregoing finding that there is a clear distinction in mineral associations between the two horizons. The amounts of Al203, total FezO3, MnO, MgO, K~.O and NazO decreased from the C to the Ae horizon although not to the same degree. The change is obviously due to leaching of certain elements associated with a selective mineral alteration from the C to the Ae horizon. The increase in Cat content in the Ae horizon was caused by saturation of the samples with calcium prior to chemical analysis. Therefore, the apparent increase in Cat suggested that the soil samples from the Ae horizon, where the three-component interstratified clays occur, had a higher cation-exchange capacity which would be expected from the vermiculite and smectite component layers of the interstratified clays. The amounts of SiOz and Tit2 increased from the C to the Ae horizon. Although small amounts of Ti may substitute for Al and Fe in silicates, most of the Tit2 content is attributed to clay-sized titanium oxide minerals (Jackson, 1964) which are relatively resistant to weathering. Therefore, the ratio of the Tit2 in the Ae horizon to that in the C horizon may be used as an indicator of the degree of weathering. The ratios ranged between 1"26 for Kedgewick and 2-97 for Tuadook.

12 306 H. Kodama and 3". E. Brydon ~ ~ ~ g t~ ~ e e,n e~ eq ~ cq e~ ~ ~ eq ~ eq f~ el o~.o

13 Clay minerals in Podzol soils 307 The free iron oxide content of the Ae horizons are low as compared to the C horizons (Table 7) or to Podzol Bf horizons (McKeague & Day, 1966). High amounts of ignition losses of the samples from the Ae horizon are due to combustion of organic matter remaining from the H~O2 treatment, which has been confirmed by the presence of an exothermic reaction at about 350 ~ C in unpublished d.t.a. curves. Weathering reactions In the Podzol soils investigated here, micas and chlorites were the principal minerals in the C horizon although chlorite in some cases had already been altered to its intergrades of various types. During weathering in the Ae horizon, the chlorites seemed to have been decomposed because there was no evidence of a trioctahedral alteration product and the magnesium and iron contents were low. Recent laboratory experiments on the acid dissolution of Mg-chlorite also have shown decomposition to an amorphous state with no evidence of a preferential degradation of the lattice (Ross, 1967a, b). On the other hand, the micas were degraded, resulting in interstratified mica-vermiculite-smectite clays. Similar reactions have been recognized in soils and have been summarized recently (Jackson, 1965). However, a further differentiation of the mineralogy of Podzol Ae horizons is noted. According to the TiO2 content ratio, the degree of weathering decreases in the following sequence : Tuadook > Serpentine > Glasier > Monquart > Kedgewick. The same sequence is shown by the X-ray data for the three-component interstratified clays of every fraction from the Ae horizon. For instance the main peaks of the clays in the minus 0-2 ~ fraction after glycerol sorption were 17"6 and 13-8 A for Tuadook, 17-4, 13-7 and 10 A for Serpentine, 17"1, 13-5 and 10 A for Galiser, 13.7 and 10 A for Monquart, and 13-3 and 10 A for Kedgewick. Since a large number of hydrated layers in the interstratified clays is reflected in a series of larger spacings, the above sequence agrees with the degree of hydration as well as with the degree of weathering. In fact, the ratio of hydrated component layers to non-hydrated (micalike) component layers of Tuadook (1-5) is higher than that of Kedgewick (0"9). In addition, the mica component layers of the interstratified clay of Kedgewick are segregated to maintain a zonal structure, whereas the interstratified clay of Tuadook has a more homogeneous distribution of each component layer. The presence of a zonal structure indicates that the interstratified clay is a weathering product of mica by a selective hydration alteration which is still in a relatively earlier stage. A continuation of the selective alteration of mica would result in a higher ratio of hydrated component layers to mica layers and more homogeneous distribution of every component layer to make a stable structure. An example of the latter case can be seen in the interstratified clay of Tuadook. The data and this interpretation suggested that the micas became altered along preferential weathering planes (Jackson et al., 1952) according to a mechanism similar to that proposed by Sudo, Hayashi &

14 308 H. Kodama and J. E. Brydon Shimoda (1962). Thus the mineral weathering observed in these soils may be expressed schematically as follows based upon the degree of weathering: Degree of weathering in Podzols ) Increase Interstratified mica-vermiculite--smectite (probably (8), (9)) Low proportion of / / hydrated layers. Mica / layers segregated Mica (7) / (illite) --\ \ \ ) Degraded mica High proportion of hydrated layers. ~ Homogeneous distribution of layers Interstratified ) Chlorite (4) Intergrade ~ (8), (9) with mica-like hydrated layers ) Amorphous residue where the bracketed numbers, represent weathering indexes as proposed by Jackson et al. (1948) and Jackson (1964). It is also proposed that these results and this weathering sequence refect the degree of podzolization. Although neither the morphology nor the chemical properties of the five soil profiles have been included in this paper, the Kedgewick, a Bisequa Podzol represents a poorly developed or 'youthful' Podzol whereas the others are well developed. The TiO2 contents and the nature of the interstratified clay minerals in the Kedgewick reflect the early stage of mica weathering in the equation above. On the other hand, the data for the well-developed Tuadook reflect the later stage of mica weathering in the above equation. The other soils seem to occupy an intermediate position and it may be that the mineralogical data might be used to subdivide further the well-developed Podzols. CONCLUSIONS The Ae horizons of the five soil series contained predominantly a dioctahedral randomly interstratified mica-vermiculite-smectite clay. Variations in the nature of the clays appeared to conform with the differences in degree of weathering. While the inherited chlorite was decomposed in all of the Ae horizons, mica was differently hydrated and transformed into an interstratified structure in which the manner of interstratification indicated the degree of weathering. According to Allen & Johns (1960) the major clay minerals in bed rocks at three localities of New Brunswick are hydrous mica and chlorite. Well-ordered mica and chlorite were found in the clay fraction of many of the C horizons of the soils reported by Brydon et al. (1968). These similarities suggest that mineral

15 Clay minerals in Podzol soils 309 association of the C horizon has been inherited from the source rock or sediment. In the present investigation, there were no large differences among the clays of the five soil series. However, in terms of TiO.~ contents and the nature of the three-component interstratified clays, podzolization in the Tuadook is considered to be more advanced than in the Kedgewick and the other series may be in an intermediate stage. ACKNOWLEDGMENTS The authors wish to thank Mr K. K. Langmaid for collecting the samples, Drs J. A. McKeague and G. J. Ross for reviewing this manuscript, Dr K. H. MacKay for calculating by an IBM computer, and Messrs N. M. Miles, B. C. Stone and L. M. Patry for their technical assistance. REFERENCES ALLEN V.T. & JOHNS W.D. (1960) Bull. geol. Soc. Am. 71, 75. BRINDLEY G.W. & GILLERY F.H. (1956) Am. Miner. 41, 169. BROWN G. (1955) Mineralog. Mag. 30, 657. BRYDON J.E., KODAMA H. & ROSS G.J. (1968) International Soil Science Congress, CESARI M., MORELLI G.L. & FAVRETTO L. (1965) Acta crystallogr. 18, 189. COLE W.F. & LANCUCKt C.J. (1966) Acta crystallogr. 21, 836. EGGLESTON R.A. & BAILEY S.W. (1967) Am. Miner. 52, 673. FORMAN S.A. & BRYDON J.E. (1961) Clay mineralogy of Canadian softs. Soils in Canada (R. F. Leggett, editor), p Royal Society of Canada, Special Publication No. 3. HAYASHI H. (~ OINIJMA K. (1964) Clay ScL 2, 22. JACKSON M.L., TYLER S.A., WILLIS A.L., BOURBEAU G.A. & PENNINGTON R.P. (1948) J. Phys. Colloid Sci. 52, JACKSON M.L., HSEUNG Y., COREY R.B., EVANS E.J. & VANDEN HEUVEL R.C. (1952) Proc. Soil Sci. Soc. Am. 16, 3. JACKSON M.L. (1964) Chemistry of the Soil (F. E. Bear, editor), Chap. 2, p. 71. Reinhold, New York. JACKSON M.L. (1965) Soil Sci. 99, 15. KODAMA H. & OINUMA K. (1963) Clays Clay Miner. 11, 236. KODAMA H., BRYDON J.E. & STONE B.C. (1967) Geochim. Cosmochim. Acta 31, 649. LANGMAID K.K. (1967) Personal communication. MAcEWAN D.M.C. (1956) Kolloidzeitrchri[t, 149, 96 MACEWAN D.M.C., Rum AMIL A. & BROWN G. (1961) The X-ray Identification and Crystal Structure o[ Clay Minerals (G. Brown, editor), Chap XI, p Mineralogical Society, London. MCKEAGUE J.A. & DAY J.H. (1966) Can. J. Soil Sci. 46, 13. MEHRA O.P. & JACKSON M.L. (1960) Clays Clay Miner. 7, 317. MILLETIE J.F.G. & LANGMAID K.K. (1963) New Brunswick Soil Survey, Report No. 5. OINUMA K. & KODAMA H. (1967) d. Toyo Univ. (Nat. Sci.) No. 7, p. 1. REYNOLDS R.C. JR (1967) Am. Miner. 52, 661. ROBERTSON G. (1950) 1. Sci. Fd Agr. 1, 59. Ross G.J. (1967a) Ca'n. J. Chem. 45, Ross G.J. (1967b) In preparation. SMITH J.V. (1956) Mineralog Mag. 31, 47. SUDO T., HAYASHI H. & SHIMODA S. (1962) Clays Clay Miner. 9, 378.