Minerals from Macedonia. Part XIX. Vibrational spectroscopy as identificational tool for some sheet silicate minerals

Journal of Molecular Structure 834–836 (2007) 318–327 www.elsevier.com/locate/molstruc

Minerals from Macedonia. Part XIX. Vibrational spectroscopy as identificational tool for some sheet silicate minerals Violeta Sˇontevska, Gligor Jovanovski *, Petre Makreski Institute of Chemistry, Faculty of Science, Sts Cyril and Methodius University, Arhimedova 5, POB 162, 1000 Skopje, Republic of Macedonia Received 8 September 2006; received in revised form 26 October 2006; accepted 29 October 2006 Available online 6 December 2006

Abstract The results of the identification of six sheet silicates originating from the Republic of Macedonia: chrysotile, Mg3Si2O5(OH)4; antigorite, (Mg,Fe2+)3Si2O5(OH)4; talc, Mg3Si4O10(OH)2; clinochlore, (Mg,Fe2+)5Al(Si3Al)O10(OH)8; cymrite, BaAl2Si2O8ÆH2O and montmorillonite, (Na,Ca)0.33(Al, Mg)2Si4O10(OH)2ÆnH2O, using vibrational spectroscopy were presented. The above mentioned minerals show IR spectral similarities in the region below 1200 cm1, mainly due to their common structural characteristics being mostly expressed in the case of isomorphous chrysotile and antigorite. Three medium bands observed in the highest wavenumber region of clinochlore originate from the stretching vibrations of the three crystallographically different OH groups. A sharp peak at 1630 cm1 was noticed only in the IR spectra of cymrite and montmorillonite being discriminative pattern between hydroxide and water-containing minerals. The similarities between the Raman spectra (1200–100 cm1) were less expressed confirming that Raman technique is more sensitive to compositional changes as well as to structural disorder. Identification was based on the comparison of the obtained results with the literature data for the corresponding minerals originating from other localities all over the world. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Sheet silicates; Identification; IR; Raman; Spectra–structure correlations

1. Introduction Sheet silicates are abundant and important minerals particularly in geological environments within roughly 20 km below the Earth’s surface. They are commonly found in intermediate and felsic igneous rocks, abundant in many (predominantly in fine grained) metamorphic, sedimentary rocks and sediments [1]. Because the spectroscopic methods have become a vital investigative tool in determinative mineralogy [2–7], in this work, we evaluate the feasibility to correlate the vibrational spectra of the collected sheet silicates with their structural characteristics. Additionally, the problems concerning the separation, purification and characterization of the minerals were discussed.

*

Corresponding author. Tel.: +389 2 3249 909; fax: +389 2 3226 865. E-mail address: [email protected] (G. Jovanovski).

0022-2860/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2006.10.026

The results from the IR spectra were compared with the corresponding literature data for the analogous mineral species. Several studies have been undertaken to obtain the IR spectra of chrysotile [8–11], antigorite [9,10,12,13], talc [9,14–17], clinochlore [16,18,19], cymrite [20] and montmorillonite [12,21]. Here should be pointed out that the IR spectrum of cymrite found in the literature is not interpreted. Having in mind that the studied minerals are natural, sometimes the identification process could be followed with some difficulties [5–7]. The Raman spectra of chrysotile [22,23], antigorite [22], talc [24], clinochlore [18,19,25], cymrite [20] (as in case with IR spectrum, published Raman spectrum of cymrite is not discussed) and montmorillonite [26] were used for the mineral characterization, as well. The results obtained by vibrational spectroscopy for the six studied sheet silicate minerals, in the nearest future, will be amended with X-ray diffraction analysis as well as elementary chemical analysis, in order to confirm and make

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fully their identification and characterization. Also, for further examinations, especially interesting is chrysotile from the point of view of its toxicity, taking into account that it belongs to the group of asbestos minerals. 2. Experimental 2.1. Samples The sheet silicate minerals were collected from various localities: chrysotile (Bogoslovec), antigorite and talc (Rzˇanovo), clinochlore (Lojane), cymrite (Nezˇilovo) and montmorillonite (Kriva Palanka). The crystals from the investigated minerals were carefully picked up under a microscope from the ore and then used in a powdered form. 2.2. Instrumentation The Perkin-Elmer FTIR system 2000 interferometer was employed for recording the spectra using the KBr pellet method. The Raman spectra of the studied samples were recorded on Bruker FT Raman model 106/S connected to FT interferometer Equinox 55 with 1064 nm line of Nd-YAG frequency laser. In order to confirm the reproducibility of the Raman spectra, an additional Raman device – computerized Dilor Z24 triple dispersive monochromator with Coherent Innova 400 argon ion laser operating at 514.5 nm for excitation, was used. Laser power of 50 or 100 mW was applied, depending on mineral sensitivity. To reduce the heating of the sample during the spectra recording process, the incident laser beam was modified in line shape focus. The measurements were carried out at a room temperature and spectral data were analyzed with the GRAMS/32 software package. 3. Crystallographic data The characteristic of the sheet silicates structure is the presence of two different types of sheets: octahedral sheets (O) and tetrahedral sheets (T). Both sheets are joined together to form layers (TOT). The layers are in turn stacked one atop another and bonded together to form the repeating unit structure of the mineral. The perfect cleavage along the c-axis is typical for the

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most sheet silicates because bonding between adjacent layers is quite weak [1]. The most important crystallographic parameters for the studied minerals are given in Table 1. The structural differences and/or similarities between the studied sheet silicates mainly arise from possible substitution of the cations in octahedral and tetrahedral sites and from interlayer cations and/or water molecules that are present in some of them [1]. The magnesian serpentine minerals antigorite, chrysotile and lizardite (the first two were studied) are 1:1 trioctahedral sheet silicates with general 2+ 3þ 3þ formula ðM2þ = 3x Mx Þ½ðSi2x Mx ÞO5 ðOHÞ4 , where M 3+ Mg, Fe, Mn and Ni and M = Al, Fe and Cr [32]. As a result of different lateral dimensions of the tetrahedral and octahedral sheets, these three varieties differ somewhat in the structure and morphology. The chemical composition of chrysotile is the closest to ideal formula Mg3Si2O5(OH)4 and it was found that there are three structural types of chrysotile: clinochrysotile, ortochrysotile and parachrysotile [29]. In the case of antigorite which is isomorphous with chrysotile and contains Mg2+ cations in octahedral coordination the substitution of Mg2+ with Fe2+ is possible. The layers in chlorite have a net negative charge because Al3+ substitutes the Si4+ cations in the tetrahedral sites. In order to balance the net negative charge, additional octahedral sheet is present in the structure of chlorite that has a net positive charge produced by substitution of Al3+ and some Fe3+ for octahedrally coordinated divalent cations. Bonding between layers involves only hydrogen bonds. Continuous solid solution extends from Mg-rich chlorite (clinochlore) to Fe-rich chlorite (chamosite). Relatively low layer charge in case of montmorillonite, which is compensated with the presence of cations in only about a third of the interlayer sites, allows water to easily move into the interlayers, causing the structure to expand [1]. The composition of the most talc samples is relatively close to the ideal formula with minor substitution of Fe, Mn or other cations for Mg in the octahedral sites and of Al for Si in the tetrahedral sites. The layers are electrically neutral, and bonding between adjacent layers depends on van der Waals and hydrogen bonds. Drits et al. [30] found that natural cymrite has a double-layer structure, with six-membered rings of (AlSi)O4 tetrahedra in the layers giving the structure a pseudohexagonal nature and with H2O molecules residing in their cavities. Also, it was shown that cymrite, BaAl2Si2O8ÆH2O, is isostructural with K-cymrite, K[AlSi3O8]ÆH2O [33].

Table 1 The most important crystallographic features of the studied sheet silicate minerals Mineral

Crystal system

Space group

˚ , b in °) Unit cell parameters (a, b, c in A

Z

Ref.

Chrysotile Antigorite Talc Clinochlore Cymrite Montmorillonite

Monoclinic Monoclinic Monoclinic Monoclinic Monoclinic Monoclinic

A2/m C2/m C2/c C2/m P21 C2/m

a = 5.3, b = 9.2, c = 7.3, b = 93 a = 81.664, b = 9.255, c = 7.261, b = 91.409 a = 5.287, b = 9.158, c = 18.95, b = 99.30 a = 5.27, b = 9.21, c = 14.36, b = 96.58 a = 5.33, b = 36.6, c = 7.67, b = 90 a = 5.17, b = 8.94, c = 9.95, b = 99.9

2 32 4 2 4 1

[27] [28] [29] [18] [30] [31]

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Table 2 Assignment of the bands in the powder infrared spectrum of chrysotile

4.1. Infrared and raman spectral study

This work

Viti and Mellinib [8]

Taylor et al.b [9]

Farmerb Foresti [10] et al.b,c [11]

Tentative assignmentd

4.1.1. Chrysotile, Mg3Si2O5(OH)4 In the IR spectrum of chrysotile, as in the spectra of other studied minerals, three well-defined spectral regions are observed (Figs. 1a and 2a). The first group of bands appear in the 3800–3600 cm1 region, the second in the 1200–800 cm1 and the third region includes the bands below 800 cm1. Two bands observed at 3688 (strong) and 3646 cm1 (weak) appear in the highest frequency region (Fig. 1a) and according to Viti and Mellini [8] are assigned as inner and outer OH stretching vibrations (see Table 2). These two bands could be attributed to the possible presence of two crystallographically different OH groups in the chrysotile structure. Three bands at 1078, 1022 and 961 cm1 are registered in the 1200–800 cm1 region and prescribed to the vibrations of the SiO4 tetrahedra (Table 2). Precisely, the first

3688 sa 3646 w 1078 s 1022 sh 961 vs – 611 s 556 vw – 455 sh 438 vs 405 w

3688 s 3640 w 1072 m 1020 w 956 vs 635 sh 608 s 560 sh 490 sh – 437 vs 425 vw

3689 s 3642 w 1078 s 1020 w 955 vs – 605 s br 555 sh 474 sh – 435 vs 406 w

3697 s 3651 w 1079 s 1022 m 957 vs 654 sh 604 s 550 sh 481 w 450 sh 432 vs –

m(OH) m(OH) m(Si–O–Si) m(Si–O–Si) m(Si–O–Si)

Absorbance

4. Results and discussion

a

b c 3800

3750 3700 3650 Wavenumber/cm –1

3600

Absorbance

Fig. 1. IR spectra of chrysotile (a), antigorite (b) and talc (c) in the OH stretching region (3800–3600 cm1).

a b

c 1300 1200 1100 1000 900 800 700 Wavenumber/cm –1

600

500 400

Fig. 2. IR spectra of chrysotile (a), antigorite (b) and talc (c) in the SiO4 region (1300–370 cm1).

a b c d

3697 s 3650 w 1080 s 1020 m 965 vs – 610 s 560 sh – 460 vw 440 vs 415 w

d(OH)

d(Si–O–Si)

s, strong; w, weak; m, medium; sh, shoulder; v, very; br, broad. Intensities are approximate because are not specified. Frequencies are approximate because are not specified. According to Viti and Mellini [8].

band (1078 cm1) is attributed to the Si–O–Si stretching vibrations, perpendicular to the basal plane, whereas the shoulder at 1022 cm1 and the most intensive band at 961 cm1 arise from the Si–O–Si vibrations in the basal plane [8]. Assignments of the bands registered below 800 cm1 in the vibrational (IR and Raman) spectra of chrysotile and the other studied minerals at this stage of the work could not be made without detailed studies, for example, isotope substitution and dilution technique. Furthermore, the bands from different vibrational modes that also appear in this region are often overlapped and overlaid. Therefore the band assignments in this region are only tentative. However, the origin of the bands at 611 and 438 cm1 in the IR spectrum of chrysotile (observed also by all four groups authors [8–11]), accompanied with several shoulders could be somewhat clearer, being attributed to the bending vibrations of OH groups and SiO4 tetrahedra, respectively. In order to confirm the identification of chrysotile as well as to check the reproducibility of the Raman spectra (Fig. 3a and b), two different excitation lines (514 and 1064 nm) were used to record the Raman spectra of chrysotile. In general, the spectra are similar (except in the region around 950 cm1 and below 150 cm1) (see Table 3) and in agreement with the corresponding literature data [22,23]. The highest frequency band in the SiO4 region observed at 1106 cm1 arise from the antisymmetric stretching vibrations of the Si–Onb–Si groups (nb – non-bridging oxygen) [22]. As mentioned before, the Raman spectrum excited with 514 nm (Fig. 3a) exhibits strong band at 944 cm1, which is not registered in Raman spectrum excited with 1064 nm (Fig. 3b) as well as in the spectra studied by Rinaudo et al. [22] and Kloprogge et al. [23]. Its origin is still not elucidated. In both Raman spectra of chrysotile, two bands are observed around 625 and 692 cm1 (Fig. 3a and b).

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Raman Intensity

a

b c

d 1200

1000

800 600 Raman shift/cm–1

400

200

Fig. 3. Raman spectra of chrysotile (a, b) excited with 514 and 1064 nm lines, respectively. Raman spectra of antigorite (c) and talc (d) excited with 514 and 1064 nm lines, respectively (1200–100 cm1).

Table 3 Assignment of the bands in the powder Raman spectrum of chrysotile This workb

This workc

Rinaudo et al.b [22]

Kloprogge et al.d [23]

Tentative assignmentf

1106 wa – – – 692 s 624 w – – – 390 s 346 w 316 vw – 233 m

1106 m 944 s – – 692 vs 626 m – – – 392 vs 348 m 320 w 306 w 235 s

1105 m – – – 692 vs 620 m – – – 389 vs 345 m – – 231 s

1102 – 709 705 692 629 466 458 432 388 345 318 304 231

mas(Si–Onb–Si)e

202 w 132 w –

206 w 132 s 118 m

–

a b c d e f

199

m(Si–O–Si) m(Mg–OH)

d(Si–O–Si) d(Si–O–Si) d(Si–O–Si) d(Si–O–Si) Onb  H–O vibrations m(Mg–O)

s, strong; w, weak; m, medium; v, very. Excitation with 1064 nm. Excitation with 514 nm. Excitation with 633 nm. Onb – non-bridging oxygens. According to Rinaudo et al. [22] and Kloprogge et al. [23].

According to Kloprogge et al. [23], the band around 625 cm1 appears from the stretching Mg–OH mode, whereas the strong band at 692 cm1, probably originate from the symmetric stretching mode of Si–O–Si groups. The bands below 400 cm1 (around 390, 350, 320, 305, 235, 205 and 130 cm1) are, in general, in agreement with the literature data [22,23]. The first four probably arise from the bending Si–O–Si vibrations, whereas the band at 235 cm1, according to Rinaudo et al. [22] is due to the vibrations of the Onb  H–O groups. The peak at 206 cm1 arises from the stretching Mg–O mode (with A1g symmetry) of the distorted MgO6 octahedra [23].

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4.1.2. Antigorite, (Mg,Fe2+)3Si2O5(OH)4 The IR spectrum of antigorite (Figs. 1b and 2b) shows expressed similarity with the spectrum of isomorphous chrysotile (antigorite contains certain amount of Fe). Namely, the IR spectra of these two minerals differ in the number of registered bands, but regarding the intensity and wavenumbers they do not differ significantly. The strong band at 3678 cm1 and the shoulder at 3699 cm1 are found in the highest frequency region (3800– 3600 cm1) and are in accordance with the bands found in the spectra studied by Farmer [10] and Mellini et al. [13] but not in a complete agreement with those found by Taylor et al. [9] and Stubicˇan and Roy [12]. These bands are attributed to the stretching vibrations of OH groups bonded to Mg in octahedral coordination [13] (Table 4). Similarly to the case of chrysotile, these highest energy bands, which are not well resolved, could arise from the presence of two crystallographically different OH groups in the structure of antigorite. In the 1100–900 cm1 region, two strong bands (1083 and 987 cm1) and shoulder (958 cm1) are observed being in agreement with the literature data (Table 4). The highest energy band arises from the Si–Onb–Si stretching vibration, whereas band at 987 cm1 is due to Si–Ob–Si stretching vibration [13]. The shoulder at 958 cm1 probably implies a slightly different structural Si–O–Si bridging configuration in this mineral [13]. Going toward lower spectral region, several bands with medium and strong intensity were registered (see Table 4). The band at 618 cm1, accompanied with the shoulder at 639 cm1 arise from the deformations of R2+O–H bonds (R2+ mainly Mg); the first from inner, whereas the second from the external O–H bonds. The band with medium intensity at 564 cm1 could be ascribed to bending SiO4 Table 4 Assignment of the bands in the powder infrared spectrum of antigorite This work

Farmerb Taylor [10] et al.b [9]

Stubicˇan and Mellini Tentative Royb,c [12] et al.b [13] assignmentf

3699 sha 3678 s 1205 vw 1083 s 987 vs 958 sh 758 vw 639 sh 618 m 564 m 506 vw 445 vs 434 sh 400 w

3700 sh 3675 s 1205 vw 1077 s 994 vs 969 sh 780 vw 646 sh 618 m 560 m 500 sh 446 vs – –

– 3670 s 1200 vw 1075 sh 980 vs – 785 vw 645 sh 625 s br 565 m – 450 vs 430 sh –

a b c d e f

– 3678 s – 1067 s 980 vs – – – 625 m 563 m – 440 vs 398 sh

3700 sh 3678 s – 1082 s br 983 vs 967 sh – 640 sh 618 br 564 m – 445 vs 436 sh –

m(OH) m(OH) m(Si–Onb–Si)d m(Si–Ob–Si) m(Si–Ob–Si) d(R2+O–H)e d(R2+O–H) d(Si–O–Si) d(Si–O–Si)

s, strong; w, weak; m, medium; sh, shoulder; v, very; br, broad. Intensities are approximate because are not specified. Frequencies are approximate because are not specified. Onb – non-bridging oxygens; Ob – bridging oxygens. R2+ mainly Mg. According to Mellini et al. [13] and Farmer [10].

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vibrations [13], whereas the strong band at 445 cm1, according to the proposed assignment by Farmer [10], originates from the bending SiO4 vibration associated with an OH translational vibration (Table 4). The lower quality Raman spectrum of antigorite (compared to the chrysotile spectrum) excited with 514 nm excitation line is presented in Fig. 3c (antigorite spectrum with 1064 nm line was of unsatisfactory quality). Similarly in case with IR spectra, the intensity and frequencies of the bands in Raman spectrum of antigorite are generally similar with those observed in the Raman spectrum of chrysotile. The bands due to the antisymmetric stretching Si–O–Si modes characterize the 1200–1000 cm1 Raman spectral region. Namely, three weak bands are registered at 1099, 1090 and 1048 cm1, whereas only the latter one is found in the studied antigorite spectrum by Rinaudo et al. [22] (Table 5). The observed bands in the lower wavenumber region (700–230 cm1) are in accordance with the literature data

Table 5 Assignment of the bands in the powder Raman spectrum of antigorite This workb 1099 w 1090 w 1048 w 682 m 628 w – 372 m 230 m 224 m 116 s a b c d

a

Rinaudo et al.c [22]

Tentative assignmentd

– – 1044 s 683 vs 635 m 520 m 375 vs 230 vs –

mas(Si–O–Si) mas(Si–O–Si) mas(Si–O–Si) ms(Si–O–Si) m(Mg–OH) d(Si–O–Si) Onb  H–O vibrations External modes External modes

s, strong; w, weak; m, medium; v, very. Excitation with 514 nm. Excitation with 1064 nm. According to Rinaudo et al. [22].

[22]. The symmetric stretching vibrations of the Si–O–Si groups give rise to the band at 682 cm1, whereas m(Mg– OH) modes are manifested by the weak band at 628 cm1. The slight shift of the latter band compared to the same band in the Raman spectrum of chrysotile (626 cm1) could be due to the higher content of Fe or Al in the octahedral sheets [22]. The band at 372 cm1 is more likely assigned as bending Si–O–Si vibration. Similarly, as in case with chrysotile, the band at 230 cm1 could be prescribed to the vibrations of the Onb  H–O groups [22] (Table 5). Two additional peaks at 224 (medium) and 116 cm1 (strong) registered in our Raman spectrum (Fig. 3c), were not observed in Raman spectrum studied by Rinaudo et al. [22]. The bands are probably due to lattice modes. 4.1.3. Talc, Mg3Si4O10(OH)2 The IR spectrum of the sample contemplated as talc is presented in Figs. 1c and 2c, whereas band assignments are given in Table 6. Main characteristic is the presence of sharp bands (Figs. 1c and 2c) being result of the high crystallinity of its structure. Namely, three sharp bands with different intensity are registered at 3677, 3661 and 3644 cm1 being in accordance with the data published by Vedder [17], but not in complete agreement with Taylor et al. [9] and Nicodom [14] (one band observed) and Smolander et al. [16] (two bands). In an ideal talc composition, Mg3Si4O10(OH)2, one sharp OH stretching band should be expected due to the complete occupancy of the octahedral layer by Mg cations. The presence of three bands in the OH stretching region of talc could be explained similarly as it was done in our previous IR study on the amphiboles [6] where depending on the presence of the Fe2+ and Mg2+ cations in the Y structural sites, the number of the bands in the OH stretching region could vary from one (if only

Table 6 Assignment of the bands in the powder infrared spectrum of talc This work a

3677 m 3661 w 3644 vw 1047 sh 1018 vs 774 vw 728 vw 669 s 533 m 465 vs 450 vs 439 sh 424 m a b c d e f

Taylor et al.b [9]

Nicodomb,c [14]

3677 m – – 1040 sh 1018 vs – – 668 s 534 m 463 vs 450 vs 440 sh 424 m

3677 m – – 1045 sh 1020 vs – – 670 s 538 m 465 vs 450 vs 440 sh 423 m

s, strong; w, weak; m, medium; sh, shoulder; v, very. Intensities are approximate because are not specified. Frequencies are approximate because are not specified. Librational modes. Translational modes. According to Russell et al. [15].

Russell et al.b [15]

1039 sh 1014 vs – – 669 s 535 m 465 vs 450 vs 440 sh 424 m

Smolander et al.b,c [16]

Vedderb [17]

Tentative assignmentf

3678 m 3660 w

3677 m 3662 w 3645 vw

m(OH) m(OH) m(OH) m3(Si–O–Si) m1(Si–O–Si)

1046 sh 1010 vs 780 w 730 sh 668 s 535 m 465 vs 450 vs 440 sh 425 m

L(OH)d m(Mg–OH) T(OH)e d(Si–O–Si)

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The lower frequency peaks in Raman spectrum of talc are characterized with weak to medium intensity and they could be prescribed to the stretching Mg–O vibrations (430, 289 and 228 cm1) and the deformation modes of the silicate network (517 and 361 cm1). The bands at 193 and 114 cm1 are most likely from the lattice modes [24] (Table 7). 4.1.4. Clinochlore, (Mg,Fe2+)5Al(Si3Al)O10(OH)8 The clinochlore belongs to the group of trioctahedral chlorites and presents an end-member of the series of the chlorite–chamosite solid solutions. Namely, if the octahedral sites in the structure are mainly occupied with Mg2+ cations, the mineral is known as Mg-rich chlorite (clinochlore), whereas if Mg2+ ions are substituted by Fe2+ cations, the mineral is recognized as chamosite (being the other end-member of the series) [29]. The infrared spectrum of clinochlore is presented in Figs. 4a and 5a and the band assignments are given in

Absorbance

Fe2+ is present) to four (if almost equal content of Mg2+ and Fe2+ is present). The three mentioned bands in the spectrum of talc (Fig. 1c) is attributed to the stretching OH vibrations where the closest octahedral sites are occupied by 3Mg2+, 2Mg2+ + Fe2+ and Mg2+ + 2Fe2+ cation combinations: [Mg2+, Mg2+, Mg2+]–OH, [Mg2+, Mg2+, Fe2+]–OH and [Mg2+, Fe2+, Fe2+]–OH, respectively. It is in agreement with the possibility of replacing Mg2+ by Fe2+ in the octahedral layer [17]. The observed strong band at 1018 cm1 as well as the shoulder at 1047 cm1 were assigned as m1(Si–O–Si) and m3(Si–O–Si) modes, respectively [15]. Additionally, the very weak bands at 774 and 728 cm1 are also found in the studied spectrum by Smolander et al. [16], but are not registered by other authors [9,14,15]. Their origin is still unknown. According to Russell et al. [15] the strong band at 669 cm1 arises from OH librations. In the 600–400 cm1 region three bands are registered at 533, 465 and 450 cm1 and are in agreement with the literature data [9,14–16] (Table 6). The highest-frequency one probably originate from the m(M–OH) vibration that involves the octahedral cations and the hydroxyl groups, whereas the second and the third band at 465 and 450 cm1 more likely appear from the translational vibrations of OH groups and Si–O–Si bending, respectively [15]. Next step in the identification of the talc sample from Rzˇanovo was interpretation of its Raman spectrum recorded using 1064 nm excitation line (Fig. 3d). The weak band at 1048 cm1 was assigned as stretching vibrations of Si– Onb–Si groups [24] (Table 7). The characteristic feature in the 680–450 cm1 is the strong band at 675 cm1 prescribed to the symmetric Si–O–Si stretching mode [24].

a d

b

e

c Table 7 Assignment of the bands in the powder Raman spectrum of talc

1048 w – – – 675 s 517 w – – 430 w 361 m – 289 m 228 w 193 vs – 114 m – a b c d e

a

Blaha and Rosascoc [24] 1049 m 1018 m 795 m 788 m 679 vs 519 w 471 m 456 m 435 m 366 s 335 w 294 m 232 m 197 vs 119 s 113 s 109 s

s, strong; w, weak; m, medium; v, very. Excitation with 1064 nm. Excitation with 514 nm. Onb – non-bridging oxygens. According to Blaha and Rosasko [24].

Tentative assignmente d

m(Si–Onb–Si)

3800

3600

1700 1660 1620 3400 3200 Wavenumber/cm –1

Fig. 4. (Left) IR spectra of clinochlore (a) cymrite (b) and montmorillonite (c) in the m(OH) and m(H2O) regions. (Right) The d(H2O) bands in cymrite (d) and montmorillonite (e).

m(Si–O–Si) d(Si–O–Si)

m(Mg–O) d(Si–O–Si) m(Mg–O) m(Mg–O) External mode External mode

Absorbance

This workb

323

a b

c 1300 1200 1100 1000 900 800 700 Wavenumber/cm –1

600

500

400

Fig. 5. IR spectra of clinochlore (a) cymrite (b) and montmorillonite (c) in the SiO4 region (1300–370 cm1).

Table 8. The appearance of three bands due to the m(OH) stretching vibrations (Fig. 4a) was connected with the same number of the crystallographically different OH groups present in its structure. The highest frequency one (with weak intensity) found at 3675 cm1 arises from the vibrations of OH groups not involved in hydrogen bonds (OH groups from 2:1 layer). The remaining two bands, which are more intense (at 3583 and 3428 cm1) were ascribed to hydroxyl groups involved in hydrogen bonds, (SiSi)O  HO and (SiAl)O  HO, respectively [19]. Two shoulders (1086 and 1059 cm1) and two very strong bands (996 and 958 cm1) are registered in the 1100–900 cm1 spectral region (found also by all three groups of authors [16,18,19]) and are assigned as stretching vibrations of the SiO4 tetrahedra (Fig. 5a and Table 8). The weak bands at 818 and 791 cm1 could be associated with tetrahedral Al–O stretchings and according to Farmer [10], their intensity increases with increasing the Al for Si substitution. Here, it is most likely that this substitution in the studied clinochlore specimen is probably low because of the very weak intensity of the mentioned bands. Metal–hydroxyl libration and translation give rise to the bands at 644 and 457 cm1, respectively, whereas very strong band at 442 cm1, registered only in the spectrum studied by Gopal et al. [18], is due to Si–O–Si bending vibration [18] (Table 8). The Raman spectrum of the studied mineral from Lojane in the 1200–100 cm1 region is characterized with the presence of well-defined peaks (Fig. 6a and Table 9). The highest-frequency peaks at 1089 and 1059 cm1, observed also by Prieto et al. [19], but not registered by Kleppe et al. [25], are attributed to antisymmetric Si–O–Si stretching modes. The symmetric Si–O–Si stretchings appear as strong bands at 679 and 540 cm1 being registered by all three groups of authors [18,19,25]. The doublet at 459 Table 8 Assignment of the bands in the powder infrared spectrum of clinochlore

Raman Intensity

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324

Smolander et al. [16]

Gopal et al.b [18]

Prieto et al.b,c [19]

Tentative assignmentf

3675 wa 3583 m 3428 m 1086 sh 1059 sh 996 vs 958 vs 818 sh 791 vw 644 s 524 m 457 vs 442 vs 413 w

3680 sh 3600 m 3450 m 1090 sh 1050 sh 1000 vs 950 vs 820 sh 780 sh 650 s 520 sh 450 s – 410 w

3678 vw 3589 m 3438 w 1090 sh 1060 sh 998 vs 958 vs 820 vw 770 vw 653 s 525 sh 453 vs 443 vs –

3675 vw 3580 m 3420 m 1090 sh 1050 sh 990 vs 960 vs 820 vw 770 vw 650 s 525 sh 460 s

m(OH) m(OH) m(OH) m(Si–O–Si) m(Si–O–Si) m(Si–O–Si) m(Si–O–Si) m(Al–O) m(Al–O) L(M–OH)d

a b c d e f

m(M–OH)e d(Si–O–Si)

s, strong; w, weak; m, medium; sh, shoulder; v, very. Intensities are approximate because are not specified. Frequencies are approximate because are not specified. Librational modes, M = Mg or Fe. M = Mg or Fe. According to Gopal et al. [18] and Prieto et al. [19].

c

d 1200

1000

800 600 Raman shift/cm –1

400

200

Fig. 6. Raman spectra of clinochlore (a) excited with 1064 nm line, cymrite (b and c) excited with 1064 and 514 nm lines, respectively, and motmorillonite (d) excited with 1064 nm line (1200–100 cm1). Table 9 Assignment of the bands in the powder Raman spectrum of clinochlore This workb 1089 wa 1059 m 679 s 540 vs 459 m 440 m 387 w 354 s 285 w 199 m 118 vw 106 w a b c d e f g h

This work

a b

Gopal et al.c [18]

Kleppe et al.c,d [25]

Prieto et al.c [19]

Tentative assignmenth

687 553 – – – 356 – – 129 106

– – 679 548 – – – 358 – 198 – 104

1083 m 1054 m 683 vs 548 vs 458 vw 445 m 390 vw 354 s 304 w 202 m

mas(Si–O–Si) mas(Si–O–Si) ms(Si–O–Si) ms(Si–O–Si) L(OH)e d(Si–O–Si) d(Si–O–Si) m(Si2O5) m1(MO6)f T(Si–O–Si)g T(Si–O–Si)

s, strong; w, weak; m, medium; v, very. Excitation with 1064 nm. Excitation with 514 nm. Raman spectrum is obtained from synthetic clinochlore. Librational modes. M = Mg or Fe. Translational modes. According to Gopal et al. [18] and Prieto et al. [19].

and 440 cm1 (not registered by Gopal et al. [18] and Kleppe et al. [25]) and the strong band at 354 cm1 probably arise from librational OH (the first one) and bending Si– O–Si modes. According to Prieto et al. [19] the intensity of latter band (354 cm1) decreases with the Si substitution by Al. The bands that appear in the lowest wavenumber region are generally in accordance with the literature data [18,19,25] (Table 9). The band at 285 cm1 was prescribed to tetrahedral movements with the symmetry species E31 , whereas sharp peak at 199 cm1 was ascribed as m(M–O) vibration of the MO6 octahedra (M = Mg and Fe) [19]. The latter two bands (118 and 106 cm1) observed in our Raman spectrum (Fig. 6a) could be prescribed to translational Si–O–Si modes [18]. 4.1.5. Cymrite, BaAl2Si2O8ÆH2O The comparison of the IR and Raman spectra of the studied sample of cymrite from Nezˇilovo with the corre-

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sponding literature data has shown that it represents the Ba-cymrite type. An attempt to interpret its IR spectrum (Figs. 4b, d and 5b) was made since, to our knowledge, no IR band assignment has been found in the literature (except for OH stretching region). Thus, the peaks at 3620, 3555 and 3498 cm1 are prescribed to H2O stretching vibrations (Fig. 4b), whereas the sharp band with medium intensity at 1627 cm1 originates from the d(H2O) vibrations (Fig. 4d), suggesting that probably only one type of crystallographically different water molecules are present in the structure of cymrite. The stretching Si–O–Si vibrations appear in the 1200– 900 cm1 region represented by four bands (1188, 1031, 955 and 921 cm1). Their wavenumbers and intensities (except for the shoulder at 1031 cm1) are in a good agreement with the corresponding bands in the published, but not discussed IR spectrum of cymrite [20]. Tentative assignment of the bands in the lower IR spectral region could be derived by analogy with the bands appearing in the IR spectra of the other studied sheet silicates (related to their common structural features) as well as by the spectral differences appeared as result of the presence of water molecules in cymrite structure. Taking into account the previous assignment of the 644 cm1 band to the L(M– OH) libration in the clinochore IR spectrum (Fig. 5a, Table 8), the band at 648 cm1 in corresponding cymrite spectrum could be attributed to the Ba–OH librations (Fig. 5b). Furthermore, the band at 478 cm1 and the shoulder at 568 cm1 presumably originate from the librational H2O modes (Table 10). The bands at 544 and 447 cm1 appear from the Si–O–Si deformations.

325

The Raman spectrum of cymrite was recorded with two different excitation lines (Figs. 6b and c). All peaks are found at almost identical frequencies and similar intensities in both Raman spectra (1064 and 514 nm) (Table 10). To our knowledge, assignments of the Raman bands for cymrite have not been performed yet. Thus, the assignment of the bands in our cymrite spectrum was based on the comparison with the IR spectrum of cymrite as well as the Raman spectra of other studied minerals. Namely, the SiO4 stretching region is characterized with the presence of weak bands at 955 and 802 cm1 due to the m3(Si–O– Si) and m1(Si–O–Si) modes, respectively. The strong peaks at 464 and 394 cm1, also registered but not discussed in the published spectrum by Graham et al. [20], probably arise the H2O librations and d(Si–O–Si) modes, respectively. The bands at 298, 125 and 108 cm1 could be tentatively prescribed to mBa–O vibrations (the first one) and external lattice modes (Table 10). 4.1.6. Montmorillonite (Na,Ca)0.33(Al,Mg)2Si4O10(OH)2ÆnH2O The IR spectrum of montmorillonite is presented on Figs. 4c, e and 5c, whereas the tentative assignment of the bands is given in Table 11. Going from the OH and H2O stretching region, two complex and broad bands at 3626 and 3421 cm1 appear, additionally associated with one shoulder at lower frequency side 3233 cm1 (Fig. 4c, Table 11). The broadening of the bands in this region is presumably due to the presence of hydrogen bonding in the montmorillonite structure. According to Farmer and Russell [21], the band at 3626 cm1 arises from the hydrox-

Table 10 Assignment of the bands in the powder infrared and Raman spectrum of cymrite Infrared This work

Raman b

Graham et al. [20]

a

3620 sh 3555 m 3498 vw 1627 m 1434 vw 1188 m 1031 sh 955 vs 921 sh 799 vw 648 s 568 sh 544 w 478 s 447 s 399 w a b c d e

3550 m 3496 m 1625 m – 1163 s – 998 vs 925 sh 791 sh 630 s 563 m

Tentative assignment

This workd

This worke

Graham et al.b,e [20]

Tentative assignment

m(H2O) m(H2O) m(H2O) d(H2O)

955 802 464 394 298 125 108

954 801 464 394 298 127 108

953 800 470 396 297 – 104

m(Si–O–Si)

m(Si–O–Si) m(Si–O–Si) m(Si–O–Si) m(Si–O–Si) L(Ba–OH) L(H2O)c d(Si–O–Si) L(H2O) d(Si–O–Si)

s, strong; w, weak; m, medium; sh, shoulder; v, very. IR and Raman spectra are obtained from synthetic cymrite. Librational modes. Excitation with 1064 nm. Excitation with 514 nm.

w w s vs m w s

vw w s s m w vs

L(H2O) d(Si–O–Si) m(Ba–O) External mode External mode

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326

Table 11 Assignment of the bands in the powder infrared and Raman spectrum of montmorillonite Infrared

Raman

This work

Farmer and Russellb [21]

Stubicˇan and Royb,c,d [12]

Tentative assignment

This workg

Frost and Rintoulg [26]

Tentative assignmenth

3626 ma 3421 m 3233 sh 1630 m 1104 sh 1031 vs 913 w 843 w 795 vw 693 sh 625 vw – 519 s 464 vs

3620 m

– 3410 w 3220 m 1630 m 1110 sh 1040 vs 925 w 840 vw 795 vw – 625 w – 525 s 470 vs

m(OH) m(H2O) 2d(H2O) d(H2O) m(Si–O–Si) m(Si–O–Si) L(OH)e L(OH)

1105 vw 911 vw 799 vw 708 m 463 w 432 vw 307 vs 282 vs 239 m 194 s 156 m 127 m

1090 915 795 708 462 430 – 285 – 198 150 141

m3(Si–O–Si) x(AlOH) x(AlOH) m1(Si–O–Si) d(Si–O–Si) L(OH)

a b c d e f g h

1102 m 1037 vs 915 w 843 w – – 627 w 595 sh 521 s 467 vs

m(M–OH)f

m1(O–H  O) m3(O–H  O) m1(AlO6) m2(AlO6) Si2O5 out-of-plane

d(Si–O–Si) m(M–O)

s, strong; w, weak; m, medium; sh, shoulder; v, very. Intensities are approximate because are not specified. Frequencies are approximate because are not specified. IR spectrum is obtained from synthetic montmorillonite. Librational modes. M = Al or Mg. Excitation with 1064 nm. According to Frost and Rintoul [26].

yl stretching vibrations. The more complex and intensive band at 3421 cm1 is apparently due to the water stretchings. The shoulder at 3233 cm1 could be prescribed to an overtone of the d(H2O) vibration found at 1630 cm1 (Figs. 4c and e). Going towards the lower wavenumbers, the shoulder at 1104 cm1 (from Si–O–Si stretching vibration perpendicular to the plane of layer) and the strong broad band at 1031 cm1 (from in-plane Si–O–Si stretching vibration) are in agreement with literature data [12,21] (Table 11). The librational OH modes appear as weak bands positioned at 913 and 843 cm1, the former one ascribed as the libration of OH coordinated to AlAl pairs, whereas the latter one as libration of OH coordinated to AlMg pairs [15]. The very weak band at 625 cm1 could not be precisely assigned, but one of the probabilities is to originate from the translational modes of the hydroxyl groups [21]. In the 550–400 cm1 spectral region strong absorption bands at 519 and 464 cm1 were observed close to the wavenumbers of the bands registered by Farmer and Russell [21] and Stubicˇan and Roy [12]. These bands presumably appear as result of bending Si–O–Si vibrations and translational modes of the octahedral ions and their adjacent oxygen layers [21]. The Raman spectrum of montmorillonite (recorded with 1064 nm excitation line) is presented in Fig. 6d and band assignments are listed in Table 11. The bands that appear in the lower energy region (350–100 cm1) are characterized by medium or strong intensity (Fig. 6d). In sharp contrast, the higher wavenumber region (1110–700 cm1) is represented by four weak bands prescribed to the

m3(Si–O–Si) mode (1105 cm1), wagging vibrations of OH groups attached to Al (911 and 799 cm1) and m1(Si–O– Si) mode (708 cm1) [26]. The bands at 463 and 432 cm1 (registered also by Frost and Rintoul [26]) are likely to appear from bending Si–O– Si modes and librational OH modes, respectively. In the 300–200 cm1 Raman spectral region three bands are registered at 307, 282 and 239 cm1, the former and the latter ones being not observed by Frost and Rintoul [26] (Table 11). The second and the third band were assigned as m1 (A1) and m3 (B2) vibrational modes of the O–H  O triangle, respectively. These vibrations would be expected when an interaction between the inner hydroxyl groups of dioctahedral montmorillonite and adjacent oxygens occurs. On the other hand, the bands below 200 cm1, generally, appear from the vibrations of the distorted AlO6 octahedron and from Si2O5 ring breathing mode (Table 11) [26]. 5. Conclusion It was shown that vibrational (IR and Raman) spectroscopy could be a vital tool for preliminary identification of the studied sheet silicate minerals collected from the Republic of Macedonia. It was also found that vibrational techniques could distinguish between the isomorphous chrysotile and antigorite, whereas the IR spectroscopy provides to discriminate the hydroxide from the water-containing minerals. The recorded Raman spectra for the studied minerals (chrysotile and cymrite) with different excitation lines confirmed the reproducibility of this technique.

V. Sˇontevska et al. / Journal of Molecular Structure 834–836 (2007) 318–327

An attempt was made to interpret the IR and Raman spectra of cymrite based on the analogy with the bands assignment in the corresponding spectra of other sheet silicates (due to their common structural features). The sharp bands in the vibrational spectra of talc provide information for high degree of structural order in this mineral. In two studied minerals, cymrite and montmorillonite, the presence of sharp band due to d(H–O–H) mode enables to conclude that water molecules are present in their structures. Acknowledgements The financial support from the Ministry of Education and Science of the Republic of Macedonia is gratefully acknowledged. The authors cordially thank Dr. Andreja Gajovic´ from Rudger Bosˇkovic´ Institute, Zagreb and Tomislav Biljan from the Faculty of Science, Zagreb, Croatia, for recording the Raman spectra of the studied minerals. References [1] W.D. Nesse, Introduction to Mineralogy, Oxford University Press, New York, 2000. [2] A. Wang, J. Han, L. Guo, J. Yu, P. Zeng, Appl. Spectrosc. 48 (1994) 959–968. [3] G.R. Hunt, J.W. Salisbury, C.J. Lenhoff, Mod. Geol. 4 (1973) 85–106. [4] E. Huang, C.H. Chen, T. Huang, E.H. Lin, J.-A. Xu, Am. Mineral. 85 (2000) 473–479. [5] P. Makreski, G. Jovanovski, S. Stojancˇeska, J. Mol. Struct. 744-747 (2005) 79–92. [6] P. Makreski, G. Jovanovski, A. Gajovic´, Vib. Spectrosc. 40 (2006) 98–109. [7] P. Makreski, G. Jovanovski, A. Gajovic´, T. Biljan, D. Angelovski, R. Jac´imovic´, J. Mol. Struct. 788 (2006) 102–114. [8] C. Viti, M. Mellini, Eur. J. Mineral. 9 (1997) 585–596. [9] D.G. Taylor, C.M. Nenadic, J.V. Crable, Amer. Ind. Hyg. Ass. J. 31 (1970) 100–108.

327

[10] V.C. Farmer (Ed.), The Infrared Spectra of Minerals, Mineralogical Society, London, 1974, pp. 331–358. [11] E. Foresti, M. Gazzano, A.F. Gualteiri, I.G. Lesci, B. Lunelli, G. Pecchini, E. Renna, N. Roveri, Anal. Bioanal. Chem. 376 (2003) 653– 658. [12] V. Stubicˇan, R. Roy, Am. Mineral. 46 (1961) 32–51. [13] M. Mellini, Y. Fuchs, C. Viti, C. Lemaire, J. Linares, Eur. J. Mineral. 14 (2002) 97–104. [14] NICODOM, Inorganic Library of FTIR spectra – Minerals, 1998. [15] J.D. Russell, V.C. Farmer, B. Velde, Mineral. Mag. 37 (1970) 869– 879. [16] K. Smolander, A. Saastamoinen, M. Ahlgren, Anal. Chim. Acta 217 (1989) 353–358. [17] W. Vedder, Am. Mineral. 49 (1964) 736–768. [18] N.O. Gopal, K.V. Narasimhulu, J.L. Rao, J. Phys. Chem. Solids 65 (2004) 1887–1893. [19] A.C. Prieto, J. Dubessy, M. Cathelineau, Clay Clay Miner. 39 (1991) 531–539. [20] C.M. Graham, J.A.K. Tareen, P.F. McMillan, B.M. Lowe, Eur. J. Mineral. 4 (1992) 251–269. [21] V.C. Farmer, J.D. Russell, Spectrochim. Acta 20 (1964) 1149. [22] C. Rinaudo, D. Gastaldi, E. Belluso, Can. Mineral. 41 (2003) 883– 890. [23] J.T. Kloprogge, R.L. Frost, L. Rintoul, Phys. Chem. Chem. Phys. 1 (1999) 2559–2564. [24] J.J. Blaha, G.J. Rosasco, Anal. Chem. 50 (1978) 892–896. [25] A.K. Kleppe, A.P. Jephcoat, M.D. Welch, Am. Mineral. 88 (2003) 567–573. [26] R.L. Frost, L. Rintoul, Appl. Clay Sci. 11 (1996) 171–183. [27] M. Szczepaniak, Med Pr. 45 (1994) 249–255. [28] G.C. Capitani, M. Mellini, Am. Mineral. 91 (2006) 394–399. [29] D. Slovenec and V. Bermanec, Sistematska mineralogija – mineralogija silikata, Denona d.o.o., Zagreb, 2003. [30] V.A. Drits, A.A. Kashaev, G.V. Sokolova, Sov. Phys. Crystal. 20 (1975) 280–286. [31] B.B. Zvyagin, Z.G. Pinsker, Dokl. Akad. Nauk SSSR+ 68 (1949) 30– 35. [32] I. Dodony, M. Posfai, P.R. Buseck, Am. Miineral. 87 (2002) 1443– 1457. [33] D.W. Fasshauer, N.D. Chatterjee, B. Marier, Phys. Chem. Mineral. 24 (1997) 455–462.