ArticlePDF Available

Abstract and Figures

Some of the most common carbonates have been investigated by non-contact Raman spectroscopy. The synthetic alkali carbonates K2CO3 and Na2CO3 have also been studied. The Raman spectrum of aurichalcite is different from that of malachite. This spectrum has a characteristic intense band at 1069 cm-1 which is assigned to the ν1 symmetric stretching mode of the carbonate unit. The two low intensity Raman lines of 1485 and 1507 cm-1 may be ascribed to the ν3 asymmetric stretching modes. To the ν4 mode (doubly degenerate symmetric bending) are attributed the values of 706 cm-1 (ν4a) and 733 cm-1 (ν4b). A number of bands with different intensities are observed in the lowest spectral shift (285, 388, 430, 461 and 498 cm-1). These Raman lines are assigned to the CuO and ZnO stretching and bending vibrations. A single band of the OH-stretching modes is observed at 3344 cm-1.
Content may be subject to copyright.
ANALELE ŞTIINŢIFICE ALE UNIVERSITĂŢII „AL. I. CUZA” IAŞI
Geologie. Tomul LV, nr. 2, 2009
THE RAMAN STUDY OF CERTAIN CARBONATES
NICOLAE BUZGAR1, ANDREI IONUȚ APOPEI1
1 „Al. I. Cuza” University of Iaşi, Department of Geology, 20A Carol I Blv.,
700505 Iaşi, Romania
Abstract
Some of the most common carbonates have been investigated by non-contact Raman
spectroscopy. The synthetic alkali carbonates K2CO3 and Na2CO3 have also been studied.
The Raman spectrum of aurichalcite is different from that of malachite. This spectrum has a
characteristic intense band at 1069 cm-1 which is assigned to the ν1 symmetric stretching
mode of the carbonate unit. The two low intensity Raman lines of 1485 and 1507 cm-1 may
be ascribed to the ν3 asymmetric stretching modes. To the ν4 mode (doubly degenerate
symmetric bending) are attributed the values of 706 cm-1 4a) and 733 cm-1 4b). A
number of bands with different intensities are observed in the lowest spectral shift (285,
388, 430, 461 and 498 cm-1). These Raman lines are assigned to the CuO and ZnO
stretching and bending vibrations. A single band of the OH-stretching modes is observed at
3344 cm-1.
Key words: nonpolarized Raman spectra, carbonates, alkali carbonates, aurichalcite
Introduction
The Raman modes of carbonates, like those of sulfates, are classified into three types
(Nakamoto, 1997): (i) vibrations of (CO3)2- groups (internal modes) (ii) vibrations of
hydroxyl molecule (in the case of hydroxyl carbonates ≈ 900 cm-1, 1500-1600 cm-1 and
3400 cm-1), and (iii) vibration modes M-O from the interactions between the cation and O
of either (CO3)2- or OH- (external or lattice modes).
The carbonate ion (CO3)2- is a nonlinear four-atomic species and it must have 3(4)-6=6
normal modes of vibrations (Cotton, 1990). These six normal modes are illustrated in
1 e-mail: nicolae.buzgar@uaic.ro
Nicolae Buzgar, Andrei Ionuț Apopei
98
figures 1 and 2. The frequency of the fundamental vibration modes of the free carbonat ion
are showed in table 1 (Scheetz and White, 1977). The ν2 mode of (CO3)2-, which is Raman
forbidden in the free ion, remains weak after coupling to the cations in the lattice.
Tab. 1 The frequency of the fundamental vibrational modes of the (CO3)2-
Type: ν4a (E')
Raman vibration around 700 cm-1 region
is due to the asymmetric bending mode.
Type: ν4b (E')
Raman modes around 700 cm-1 region
are due to the asymmetric bending mode.
Fig. 1 Illustration for normal modes of vibration; displacement vectors are represented by arrows
Mode Symmetry Selection
Rules Frequencies (cm
-
1
)
Scheetz and White (1977)
ν1
Nondegenerate symmetric
stretch A'1 Raman 1064
ν2 Nondegenerate symmetric
(out-of plane) bend A''2 IR -
ν3 Doubly degenerate
asymmetric stretch E' IR+Rama
n 1415
ν4 Doubly degenerate
asymmetric (in-plane) bend E' IR+Rama
n 680
The Raman study of certain carbonates
99
Type: ν2 (A''2)
Infrared modes near 800 cm-1 are derived
from the symmetric bending mode.
Type: ν1 (A'1)
Strong Raman modes due to the
symmetric stretching vibration of the
carbonate groups appear around 1050 cm-
1.
Type: ν3a (E')
Weak Raman peaks near 1400 cm-1 are
due to the asymmetric stretch.
Fig. 2 Illustration for normal modes of vibration; displacement vectors are represented by arrows.
Nicolae Buzgar, Andrei Ionuț Apopei
100
Type: ν3b (E')
Weak Raman peaks near 1400 cm-1 are
due to the asymmetric stretch.
Fig. 2 (continued from the previous page)
Analytical procedure
Raman spectra were obtained at room temperature with a Horiba Jobin-Yvon RPA-HE
532 Raman Spectrograph with multichannel air cooled (-70 °C) CCD detector, using a
doubled frequency NdYag laser, 532 nm/100 mW nominal power. The spectral resolution
is 3 cm-1/pixel, and the spectral range between 200 and 3400 cm-1. Raman system includes
a “Superhead” fibre optic Raman probe for non contact measurements, with an 50X LWD
Olympus visible objective, NA = 0.50 WD = 10.6 mm.
Data acquisition was performed by 2-20 seconds exposure, 5-30 acquisitions, at laser
magnification of 90-100%, to improve the signal-to-noise ratio. Spectra manipulations
consists of a basic data treatment, such as baseline adjustment and peak fitting (Lorentz
function).
Samples
The samples used in the study are listed in table 2. The first nine samples with their
sample number, belong to the collection of Grigore Cobălcescu Mineralogy and
Petrography Museum of the “Alexandru Ioan Cuza” University of Iassy. The other two
samples were synthetic alkaly carbonates.
Results and discussions
A. Anhydrous carbonates
1. Calcite group
Three samples of minerals are used from the calcite group: calcite, siderite and
rhodochrosite. The nonpolarized Raman spectra of the calcite, siderite and rhodochrosite
are shown in figure 3.
The Raman study of certain carbonates
101
Tab. 2 Samples used in the study
The Raman spectra of these minerals are very similar. The intense band (ν1) of the
calcite spectrum corresponds to the symmetric stretching of CO3 group at 1087 cm-1. The ν2
(symmetric bending) vibration mode does not appear. The Raman lines attributed to ν3
(asymmetric stretching) mode and ν4 (asymmetric bending) mode have 1437 cm-1,
respectively 714 cm-1. The Raman spectrum of siderite is characterized by the same Raman
band corresponding to the symmetric stretching of CO3 group as that of the calcite, at 1087
cm-1. The band at 1442 cm-1 corresponds to the ν3 normal mode and 736 cm-1 to the ν4 (O-
C-O in-plane bending) mode. The Raman spectrum of rhodochrosite consists of a strongest
intensity band at 1094 cm-1 assigned to the ν1symmetric stretching mode of CO3 group.
The ν3 normal mode appears at 1439 cm-1 and the ν4 normal mode at 725 cm-1.
The lower wavenumbers of calcite (285 cm-1), siderite (289 cm-1) and rhodochrosite
(292 cm-1) observed in figure 3 arise from the external vibration of the CO3 groups that
involve translatory oscillations of those groups (relative translations between the cation and
anionic group). There are no values below 200 cm-1 because the Raman shift is 200-3400
cm-1.
A weak lines observed at 1749, 1729 and 1752 cm-1 may be regarded as the
combination bands of ν1+ ν4 modes (Gunasekaran et al., 2006). The spectrum of siderite
presents a band at 514 cm-1, which may be assigned to the vibration of a Fe-O bond.
The observed vibrational bands of calcite, siderite and rhodochrosite were compared
with their documented values and are listed in table 3. The positions of the observed Raman
bands are in agreement with those reported by Gunasekaran et al. (2006) for calcite and
Beny (1991) for siderite and rhodochrosite. The minor shift in positions may be due to the
effect of natural impurities present in the samples.
Mineral Sample no. Location
1.
Calcite 5413 Guanajuato – Mexico
2.
Siderite 5455 Lobenstein – Germany
3.
Rhodochrosite 5438 Kohlenbach – Germany
4.
Aragonite 5421 Spania Dolina – Slovakia
5.
Witherite 5484 Alston – England
6.
Strontianite 5432 Drensteinfurt – Germany
7.
Azurite 5397 Namibia
8.
Malachite 5393 Eisenzeche – Germany
9.
Aurichalcite 5457 Lavrio - Greece
10.
KCO
3
- Synthetic
11.
Natrite -
Nicolae Buzgar, Andrei Ionuț Apopei
102
Fig. 3 Raman spectrum of calcite compared with those of siderite and rhodochrosite.
2. Aragonite group
The Raman spectra for the aragonite, witherite and strontianite are shown in figure 4.
The spectra of these investigated samples show only five bands out of the 30 predicted
Raman-active modes (Krishnamurti, 1960; Urmos et al., 1991). These spectra are governed
by the very strong Raman line atributed to the ν1 symmetric stretching mode of the
carbonate group. The wavenumbers of this Raman band are 1083, 1069 and 1059 cm-1 (tab.
4). They are similar to those reported by Urmos et al. (1991), Krishnamurti (1960) and
Beny (1989).
Calcite
Siderite
Rhodochrosite
The Raman study of certain carbonates
103
Tab. 3 Raman bands in calcite, siderite and rhodochrosite (cm-1)
Calcite Siderite Rhodochrosite Free
CO32- Assignment
This
study
et al., 2006 This
study
Beny
(1991)
This
study
Beny
(1991)
89 R*(CO
3
)
162 190 184 T(Ca, CO
3
)
285 288 289 294 293 289 T(Ca, CO
3
)
514 506 T(Fe, CO
3
)
715
716
737
731
742 726
718
680
ν4-Asymmetric bending mode
879 ν
2
-Symmetric bending mode
1087
1092
1087
1087
1094
1064
1085 1063
ν1-Symmetric stretching mode
1437
1437 1442 1439 1414 1415 ν
3
-Asymmetric stretching mode
1749
1754
1729
1726
1733 1752
1725
ν1+ ν4
R* - rotational
The Raman lines atributed to the ν3 asymmetric stretching mode can be obseerved at
1422 and 1511 cm-1 for witherite, 1445 and 1543 cm-1 for strontianite, respectively 1461
and 1573 cm-1 for aragonite. The appearance of two lines corresponding to ν3 is in
accordance with the splitting of ν3 predicted by theory. The Raman lines at 693, 700 and
701 cm-1 were assigned to the ν4 normal mode. The ν2 vibration mode are not visible in our
spectra. The Raman bands due to the external vibration mode for aragonite, strontianite and
witherite have the frequencies 250, 242 and 227 cm-1. The frequencies of all Raman bands
observed in this study can be corelated with the atomic masses of the cations.
3. Alkali carbonates
The Raman spectrum of K2CO3 (fig. 5) shows a couple of bands at 1026 and 1063 cm-1
that may be attributed to the ν1 symmetric stretching mode (tab. 5). The two bands may be
explained by the presence of the molecules belonging to two structures, C2v bidentate form
and D3h, in agreement with the theoretical values calculated by Koura et al. (1996). The ν2
vibration mode is not Raman active. The bands at 1374 cm-1 and 1426 cm-1, can be assigned
to ν3a respectively ν3b. To the ν4 mode (doubly degenerate asymmetric bending) are
attributed the values of 677 cm-1 4a) and 702 cm-1 4b). The spectrum also presents three
bands at 237 cm-1, 287 cm-1 and 484 cm-1, which may be assigned to the external vibration
modes between the cation and anionic group (T(K,CO3)).
Nicolae Buzgar, Andrei Ionuț Apopei
104
Fig. 4 Raman spectra of aragonite, strontianite and witherite.
The Raman study of certain carbonates
105
Tab. 4 Raman bands in aragonite, strontianite and witherite (cm-1)
Aragonite Strontianite Witherite
Assignment
This
study Urmos
(1991) Krishnamurti
(1960) This
study
Krishnamurti
(1960) This
study
Krishnamurti
(1960) Beny
(1989)
250 284 285 242 246 227 227 224 T(M,CO
3
)
701 701
705
-
702
707
716
700
-
-
701
711
-
693
-
-
691
699
-
690
696
- ν4
NO 853 854 NO 855 NO 852 - ν
2
1083 1085 1086 1069 1074 1059
1061 1035
1059 ν1
-
1461
1573
-
1462
1547
-
1415
1463
-
1445
1543
1408
1438
1447
-
1422
1511
1394
1409
1421
-
1419
1505 ν3
NO 2165 NO 2116*
1
NO = not observed; NA = not assigned
Tab. 5 Frequencies of the Raman lines of the alkali carbonates
K
2
CO
3
Na
2
CO
3
Assignment
This
study Koura et al. (1996) This
study Beny
(1988) Burgio and
Clark (2001)
Calculated Measured
237,
288,
484
76, 85,
122, 252,
278, 291
126, 141
192 290 111, 131
149, 171
189 NI* T (K,CO3)
T (Na, CO3)
677 688 692 702 701 702
ν4a (
E'
) Asymmetric bending
mode
702 706 697 ν4b (
E'
) Asymmetric bending
mode
1026
1063 1025 1043
1064 1080 1069
1079 1071
1081 ν1 (
A'
1) Symmetric stretching
mode
1374 1385 1405 1429 1421 NI*
ν3a (
E'
) Asymmetric stretching
mode
1426 1557 1431 ν3b (
E'
) Asymmetric stretching
mode
NI – Raman bands which appear in the figure 48 (Burgio and Clark, 2001) but without determined
frequencies
For Na2CO3, the most intense Raman band, corresponding to the ν1 symmetric
stretching vibration of the carbonate group, is at 1080 cm-1. The 1429 cm-1 peak
Nicolae Buzgar, Andrei Ionuț Apopei
106
corresponds to the ν3 normal mode and line of 702 cm-1 is attributed to the ν4 asymmetric
bending mode. The Raman spectrum of Na2CO3 shows only one line of lattice mode, at 290
cm-1. The wavenumbers of Raman lines for two alkali carbonates are presented in table 5.
Fig. 5 Raman spectra of alkali carbonates (synth.)
The Raman study of certain carbonates
107
B. Carbonates with hydroxyl
1. Azurite
The spectrum of azurite is shown in figure 6. The wavenumbers of the detected bands
are reported in table 6. This azurite spectrum is characterized by several lines that cover the
spectral range of 200-1600 cm-1. The bands observed up to 600 cm-1 are assigned to the
translations of (Cu, CO3) and those observed up to 1600 cm-1 are assigned to CO3 complex
(Frost et al., 2002). The Raman spectrum of our azurite does not show the O-H stretching
band at about 3400 cm-1.
Fig. 6 Raman spectrum of azurite in the 200-3400 cm-1 region
Azurite has a characteristic intense band at 404 cm-1. The ν1 symmetric stretching band
of the carbonate ion is observed at 1098 cm-1. The bands attributed to the carbonate 3)
asymmetric stretching vibration appear at 1425 cm-1 and 1459 cm-1. One band is observed
in the Raman spectrum of azurite at 766 cm-1 and is assigned to the ν4 mode. The band of
835 cm-1 was assigned to the ν2 symmetric bending vibration. A number of bands with
different intensities are observed in the lowest spectral shift of the Raman spectrum of
Nicolae Buzgar, Andrei Ionuț Apopei
108
azurite (250, 285, 339, 404 and 544 cm-1). These Raman lines are assigned to the lattice
modes. The O-H out-of-plane bending mode of azurite was reported at 939 cm-1. We have
not found any information available for Raman line of 1579 cm-1. It is probably due to the
O-H bending mode, in agreement with Nakamoto (1997).
Tab. 6 Raman bands of azurite (cm-1)
This study Azurite Assignment
Frost et al., 2002 Mattei et al., 2008
250, 285, 339,
404, 544
112, 131, 139, 144, 154, 165, 171,
179, 194, 215, 237, 248, 265, 281,
332, 387, 400, 414, 540
157, 174, 182, 240,
250, 267, 282, 332,
387, 402, 542 T(Cu, CO3)
766 739
764 744
768 ν4-Asymmetric CO3
bending mode
835 815
835 840 ν2-Symmetric CO3
bending mode
939 952 937 O-H out-of-plane
bending mode
1097 1095 1099 ν1-Symmetric CO3
stretching mode
1425
1459 1421
1431 1422
1433
1462
ν3-Asymmetric CO3
stretching mode
1579 1582 O-H bending mode
NO 3424
3446 3431 O-H stretching mode
NO = not observed
2. Malachite
The Raman spectrum of malachite is shown in figure 7. Malachite has two
characteristic very strong bands at 435 and 1495 cm-1.
As in the case of azurite, the Raman bands at the lowest region of the spectrum of
malachite (fig. 7) can be attributed to the lattice modes (tab. 7). In this region the spectrum
shows an intense band at 435 cm-1, and the others at: 215, 270, 354, 537 and 597 cm-1.
The characteristic bands for the CO3 group are observed at: 1059 and 1098 cm-1 for the
ν1 symmetric stretching modes (of two different CO3 groups – doubly degenerate mode);
820 cm-1 attributed to the ν2 symmetric bending mode (Frost et al., 2002); 1368, 1462 and
1495 cm-1 assigned to the ν3 asymmetric stretching modes; 722 and 755 cm-1 for ν4
asymmetric bending (doubly degenerate mode). For the hydroxyl-stretching region, the
The Raman study of certain carbonates
109
spectrum shows bands at 3310 and 3382 cm-1. The vibration mode of the hydroxyl group
(O-H bending mode) appears at 1639 cm-1.
Differences between the spectra of malachite and azurite may be explained by the
molecular structure of azurite being based upon a distorted square planar arrangement
compared with a distorted octahedral arrangement of the copper in malachite (Frost et al.,
2002).
Fig. 7 Raman spectrum of malachite in the 200-3400 cm-1 region.
3. Aurichalcite
The Raman spectrum of aurichalcite is different from those of malachite and azurite.
This spectrum has a characteristic intense band at 1069 cm-1 which is assigned to the ν1
symmetric stretching mode of the carbonate unit (fig. 8, tab. 8).
The two low intensity Raman lines of 1485 and 1507 cm-1 may be ascribed to the ν3
asymmetric stretching modes. To the ν4 mode (doubly degenerate asymmetric bending) are
attributed the values of 706 cm-1 4a) and 733 cm-1 4b). A number of bands with different
intensities are observed in the lowest spectral shift of the aurichalcite Raman spectrum
(285, 388, 430, 461 and 498 cm-1). These Raman lines are assigned to the CuO and ZnO
Nicolae Buzgar, Andrei Ionuț Apopei
110
stretching and bending vibrations (Frost et al., 2007). A single band of the OH-stretching
modes is observed at 3344 cm-1.
Tab. 7 Raman bands in malachite (cm-1)
This study Malachite Assignment
Frost et al. (2002) Mattei et al. (2008)
215, 269, 354,
434, 536, 596 130, 142, 151, 166, 176,
205, 217, 267, 294, 320,
249, 389, 429, 514, 531,
563, 596
157, 171, 182, 204, 224,
272, 352, 435, 513, 537,
601 T(Cu, CO3)
722
755 718
750 723
753 ν4-Asymmetric CO3
bending mode
820 807
817 ν2-Symmetric CO3
bending mode
1059
1097 1098 1058
1101 ν1-Symmetric CO3
stretching mode
1368
1462
1495
1365
1423
1493
1514
1370
1463
1497 ν3-Asymmetric CO3
stretching mode
1639 O-H bending mode
3310
3382 3349
3380 3380 O-H stretching mode
Fig. 8 Raman spectrum of aurichalcite
The Raman study of certain carbonates
111
Tab. 8 Raman bands in aurichalcite (cm-1)
This study Frost et al. (2007) Assignment
285, 388, 430,
461, 498 278-283, 388-392,
428-432, 460-463,
498-499
T(Cu, CO3) and
T(Zn, CO3)
706
733
-
708-711
733-737
748-753 ν4-Asymmetric CO3 bending mode
- 849-860 ν2-Symmetric CO3 bending mode
1000
1069
-
1020
1060-1065
1071-1072 ν1-Symmetric CO3 stretching mode
1485
1507 1485
1506-1511 ν3-Asymmetric CO3 stretching
mode
3344 3338-3355 O-H stretching mode
Conclusions
In all spectra the three fundamental vibration modes of (CO3)2- were observed, with
variations in band positions and splitting, caused by the influences of the different
structures and cations.
The measured Raman bands of analyzed carbonates are similar to those reported in
literature (ν1 between 1000-1100 cm-1, ν2 -800-900 cm-1, ν3 - 1400-1500 cm-1, ν4 - 690-790
cm-1). The slight differences between some Raman spectra were probably caused by either
the instruments and techniques or the composition of the minerals.
Although the ν2 vibration mode is not normally active in Raman, it makes an exception
in the case of the azurite and malachite samples.
The frequencies of all Raman bands of the orthorhombic carbonates (the aragonite
group) can be corelated with the atomic masses of the cations. In the case of trigonal
carbonates (the calcite group), the frequencies of the vibrational modes of (CO3)2- and the
atomic masses of cations cannot be correlated.
The Raman spectrum of malachite and aurichalcite are different although the two
minerals have similar structures.
Acknowledgments
This work has been supported by Romanian Ministry of Education, Research and
Innovation under a PNCDI II – IDEI grant PCE no. 795/2009.
Nicolae Buzgar, Andrei Ionuț Apopei
112
References
Beny, C., 1988. Société Française de Minéralogie et de Cristallographie - Base de données de spectres Raman.
Natrite; quoted from http://wwwobs.univ-bpclermont.fr/sfmc/ramandb2/fpdf/UTIL81.pdf
Beny, C., 1989. Société Française de Minéralogie et de Cristallographie - Base de données de spectres Raman.
Witherite; quoted from http://wwwobs.univ- bpclermont.fr/sfmc/ ramandb2/fpdf/WITHE11.pdf
Beny, C., 1991. Société Française de Minéralogie et de Cristallographie - Base de données de spectres Raman.
Siderite, Rhodochrosite; quoted from http://wwwobs.univ-bpclermont.fr/sfmc/ramandb2/fpdf/SIDER31.pdf
Burgio, L., Clark, R.J.H., 2001. Library of FT-Raman spectra of pigments, minerals, pigment media and varnishes,
and supplement to existing library of Raman spectra of pigments with visible excitation. Spectrochimica
Acta, Part A, 57, 1491-1521.
Cotton, F.A., 1990. Chemical applications of group theory. Third edition. Wiley-Interscience, Texas.
Frost, R.L., Hales, M.C., Reddy, B.J., 2007. Aurichalcite – A SEM and Raman spectroscopic study. Polyhedron,
26, 3291-3300.
Frost, R.L., Martens, W.N., Rintoul, L., Mahmutagic, E., Kloprogge, J.T., 2002. Raman spectroscopic study of
azurite and malachite at 298 and 77 K. Journal of Raman Spectroscopy, 33, 252-259.
Gunasekaran, S., Anbalagan, G., Pandi, S., 2006. Raman and infrared spectra of carbonates of calcite structure.
Journal of Raman Spectroscopy, 37, 892-899.
Koura, N., Kohara, S., Takeuchi, K., Takahasi, S., Curtiss, L.A., Grimsditch, M., Saboungi, M.L., 1996. Alkali
carbonates: Raman spectroscopy, ab initio calculations and structure. Journal of Molecular Structure, 382,
163-169.
Krishnamurti, D., 1960. The Raman spectra of aragonite, strontianite and witherite. Indian Academy of Sciences.
Mattei, E., Vivo, G., Santis, A., Gaetani, C., Pelosi, C., Santamaria, U., 2008. Raman spectroscopic analysis of
azurite blackening. Journal of Raman Spectroscopy, 39, 302-306.
Nakamoto, K., 1997. Infrared and Raman Spectra of Inorganic and Coordination Compounds. Part A: Theory and
Applications in Inorganic Chemistry. John Wiley and Sons, New York.
Nakamoto, K., 2009. Infrared and Raman Spectra of Inorganic and Coordination Compounds. Part A: Theory and
Applications in Inorganic Chemistry. (Sixth edition). John Wiley and Sons, New Jersey.
Scheetz, E.B., White, B.W., 1977. Vibrational spectra of the alkaline earth double carbonates. American
Mineralogist, 62, 36-50.
Urmos, J., Sharma, S.K., Mackenzie, F.T., 1991. Characterization of some biogenic carbonates with Raman
spectroscopy. American Mineralogist, 76, 641-646.
... The Raman characteristics for carbonate unit are well revealed in Fig. 2. The strongest Raman band at 1077 cm -1 is assigned to the intense symmetric C-O stretching mode (ν1) and relatively weak bands at 700 and 726 cm -1 correspond to C-O asymmetric in-plane bending modes (ν4) (Bühn et al., 1999;Buzgar and Apopei, 2009;Chakhmouradian and Dahlgren, 2021). The C-O out-of-plane bending signals (ν2) at 870-880 cm -1 , which occur in some anhydrous carbonates, are not observed in gysinite-(La). ...
... The C-O out-of-plane bending signals (ν2) at 870-880 cm -1 , which occur in some anhydrous carbonates, are not observed in gysinite-(La). In addition, a weak line at 1443 cm -1 is probably assigned to the C-O ν3 asymmetric stretching mode, which is also observed in bastnäsite and aragonite group minerals (Frost and Dickfos, 2007;Buzgar and Apopei, 2009), and lines around 1738 cm -1 may be regarded as the combination bands of ν1 + ν4 modes (Gunasekaran et al., 2006). The bands of H2O present at 3249 and 3549 cm -1 correspond to the O-H asymmetric and symmetric ν1 stretching modes, respectively, and band at 1612 cm -1 is assigned to O-H ν2 bending mode (Carey and Korenowski, 1998). ...
Article
The new mineral, gysinite-(La), with the ideal formula LaPb(CO3)2(OH)·H2O, has been discovered in lujavrite from the Saima alkaline complex, Liaoning Province, China. It commonly occurs as subhedral to anhedral, granular and platy crystals of 5 to 50 μm in size, in interstices or enclosed in microcline, aegirine and nepheline. Associated minerals include nepheline, aegirine, microcline, natrolite, eudialyte, lamprophyllite, bastnäsite-(Ce), parasite-(Ce), ancylite-(La), ancylite-(Ce), bobtraillite, britholite-(Ce), thorite, calcite and galena. The crystallization of gysinite-(La) may be related to the post-magmatic carbonation event. Gysinite-(La) crystals are generally transparent, colourless, or pale yellow, with a vitreous lustre and white streak. It is brittle with an uneven fracture, and the estimated Mohs hardness is 3½ to 4. The calculated density is 5.007 g/cm3. Optically, gysinite-(La) is biaxial (–), α= 1.832(2), β= 1.849(4), γ = 1.862(5) in white light, and 2Vmeas = 81.6°. The empirical formula of gysinite-(La) is (La0.93Pb0.61Nd0.23Pr0.14Sr0.04Gd0.02Sm0.01Eu0.01Ca0.01)Σ2(CO3)2(OH)1.34·0.66H2O, which is calculated on the basis of general formula (REExM2+2-x)(CO3)2(OH)x·(2-x)H2O. The strongest eight lines of its powder XRD pattern [d, Å (I, %) (hkl)] are: 5.596 (21) (011), 4.349 (100) (110), 3.732 (68) (111), 2.984 (61) (121), 2.667 (21) (031), 2.363 (48) (131), 2.090 (29) (221), and 2.028 (21) (212). Gysinite-(La) is orthorhombic, in the space group Pmcn, and unit-cell parameters refined from single-crystal X-ray diffraction data are: a = 5.0655(2) Å, b = 8.5990(3) Å, c = 7.3901(4) Å, V = 321.90(2) Å3 and Z = 2. It is a new member of the ancylite group and isostructural with gysinite-(Nd), while the occupancies of La and Pb are dominant in the metal cation site in structure.
... The sample is mainly represented by crystalline Na 2 CO 3 ( Table 3, Fig. 5a). The Raman spectrum of sodium carbonate corresponds to the c-Na 2 CO 3 stable at ambient P-T conditions (Buzgar and Apopei, 2009) (Fig. 6a). A thin ($6 lm) zone of Na 2 Fe 3 O 4 with a minor amount of iron phase (Fe or iron carbide) appears on the Fe capsule walls (Fig. 5b). ...
... 5e, low-left corner). The Raman spectrum of sodium carbonate corresponds to the c-Na 2 CO 3(Buzgar and Apopei, 2009) (Fig. 6a). A 22-lm zone ...
Article
Full-text available
It is generally accepted that carbonates can be subducted to the mantle depths, where they are reduced with iron metal to produce a diamond. In this work, we found that this is not always the case. The mantle carbonates from inclusions in diamonds show a wide range of cation compositions (Mg, Fe, Ca, Na, and K). Here we studied the reaction kinetics of these carbonates with iron metal at 6-6.5 GPa and 1000-1500 °C. We found that the reduction of carbonate with Fe produces C-bearing species (Fe, Fe-C melt, Fe3C, Fe7C3, C) and wüstite containing Na2O, CaO, and MgO. The reaction rate constants (k = Δx²/2t) are log-linear relative to 1/T and their temperature dependences are determined to be kMgCO3 (m²/s) = 4.37 × 10⁻³ exp [−251 (kJ/mol)/RT] kCaMg(CO3)2 (m²/s) = 1.48 × 10⁻³ exp [−264 (kJ/mol)/RT] kCaCO3 (m²/s) = 3.06 × 10⁻⁵ exp [−245 (kJ/mol)/RT] and kNa2CO3 (m²/s) = 1.88 × 10⁻¹⁰ exp [−155 (kJ/mol)/RT]. According to obtained results at least, 45-70 vol.% of carbonates preserve during subduction down to the 660-km discontinuity if no melting occurs. The slab stagnation and warming, subsequent carbonate melting, and infiltration into the mantle saturated with iron metal are accompanied by a reduction of carbonate melt with Fe. The established sequence of reactivity of carbonates: FeCO3 ≥ MgCO3 > CaMg(CO3)2 > CaCO3 >> Na2CO3, where K2CO3 does not react at all with iron metal, implies that during reduction carbonate melt with Fe evolves toward alkali-rich. The above conclusions are consistent with the findings of carbonates in inclusions in diamonds from the lower mantle and high concentrations of alkalis, particularly K, in mantle carbonatite melts entrapped by diamonds from kimberlites and placers worldwide.
... Raman spectra of L1 and L4 painted lines are shown in Figure 3. In detail, the 3 layers of the L1 line presented the following characteristics: the upper one was black, composed of amorphous carbon black (graphite), recognizable by the two characteristic Raman bands at 1325 cm −1 and 1580 cm −1 [32,33], mixed with calcite, having a strong peak at 1081 cm −1 (CO3 symmetric stretching [34,35]); the intermediate layer was a visible brownish/greyish color and was composed of a mixture of calcite, graphite, hematite (characteristic peaks at 286, 410, 614 cm −1 due to Fe-O symmetric stretching [36,37]), and gypsum with a strong band at 1006 cm −1 related to -SO4 symmetric stretching [38,39]; the last one was a mixture of hematite, calcite, calcium hydroxide (large band at 780 cm −1 [40]), and gypsum. Line L4 of the F.02 sample was composed of a single pink layer with the same composition of the just mentioned layer of L1. ...
Article
Full-text available
Photoacoustic (PA) imaging is a novel, powerful diagnostic technique utilized in different research fields. In particular, during recent years it has found several applications in Cultural Heritage (CH) diagnostics. PA imaging can be realized in transmittance or epi-illumination (reflectance) modes, obtaining variable levels of contrast and spatial resolution. In this work, we confirmed the applicability of the PA technique as a powerful tool for the imaging of one of the most challenging artwork objects, namely fresco wall paints, to obtain precise stratigraphic profiles in different layered fresco samples. In this regard, we studied some multi-layered fragments of the vault of San Giuseppe Church in Cagliari (1870 AD) and some mock-ups realized specifically to test the potentiality of this technique. Due to complex structures of the frescoes, we used the Spatially Off-set Raman Spectroscopy (SORS) technique to provide complementary information. The experimental results were in agreement for both techniques, even for the three-layered complex structure, and were confirmed with Scanning Electron Microscopy (SEM) analysis of cross-sections. The combined use of these two techniques proved useful to investigate detailed hidden information on the fresco samples.
... In both samples, these vibrations correspond to the BaCO 3 polymorph aragonite-type, named witherite. 112,113 In these samples, the band corresponding to kerogen was not identified; hence, they are considered of abiotic origin. In the barium samples synthesized in the presence of DNA from E. coli obtained at high or low CO 2 , the characteristic peaks of witherite were identified plus three peaks approximately at 1300, 1600, and 2900 cm −1 ( Table 3). ...
Article
Full-text available
The origin of life on Earth is associated with the Precambrian era, in which the existence of a large diversity of microbial fossils has been demonstrated. Notwithstanding, despite existing evidence of the emergence of life many unsolved questions remain. The first question could be as follows: Which was the inorganic structure that allowed isolation and conservation of the first biomolecules in the existing reduced conditions of the primigenial era? Minerals have been postulated as the ones in charge of protecting theses biomolecules against the external environment. There are calcium, barium, or strontium silica-carbonates, called biomorphs, which we propose as being one of the first inorganic structures in which biomolecules were protected from the external medium. Biomorphs are structures with different biological morphologies that are not formed by cells, but by nanocrystals; some of their morphologies resemble the microfossils found in Precambrian cherts. Even though biomorphs are unknown structures in the geological registry, their similarity with some biological forms, including some Apex fossils, could suggest them as the first "inorganic scaffold" where the first biomolecules became concentrated, conserved, aligned, and duplicated to give rise to the pioneering cell. However, it has not been documented whether biomorphs could have been the primary structures that conserved biomolecules in the Precambrian era. To attain a better understanding on whether biomorphs could have been the inorganic scaffold that existed in the primigenial Earth, the aim of this contribution is to synthesize calcium, barium, and strontium biomorphs in the presence of genomic DNA from organisms of the five kingdoms in conditions emulating the atmosphere of the Precambrian era and that CO2 concentration in conditions emulating current atmospheric conditions. Our results showed, for the first time, the formation of the kerogen signal, which is a marker of biogenicity in fossils, in the biomorphs grown in the presence of DNA. We also found the DNA to be internalized into the structure of biomorphs.
Article
Carbonates play a crucial role in the water and carbon cycles of both geochemical and cosmochemical environments. As carbonates do not exist homogeneously with other minerals in rocks and sands of various sizes, an analytical method that simultaneously satisfies non-destructivity and high spatial resolution has been desired. Further, the ability of semi-quantitative analysis with carbonates-selectivity and without any pre-treatments is added, for its applicability would be extended to remote sensing for deep sea and outer spaces. Here, we focused on the application of micro-Raman spectroscopy, where the vibrational wavenumbers of the translational (T) and librational (L) modes of carbonates are sensitively related to their cation composition. By comparing the semi-quantitative information obtained by X-ray fluorescence spectroscopy, it was found that these vibrational wavenumbers are approximately linearly related to the cation composition. Consequently, a conversion matrix was proposed to estimate the cation composition from the T and L mode vibrational wavenumbers. This method is universally applicable to any cation composition in carbonates, with no background information on the analyte required. To improve the accuracy, conversion matrices were further optimized to three solid-solution series of carbonates. It is worth noting that the proposed conversion matrices are free from matrix effects and do not depend on the total amount of carbonate in a sample. Therefore, the proposed method provides a useful analytical basis for remote sensing of the cation composition of carbonates, both in terrestrial and extra-terrestrial environments.
Article
Full-text available
Plain Language Summary As a biosedimentary response to the end‐Permian mass extinction, the widespread occurrence of microbialites has attracted increasing levels of interests from geologists worldwide. However, the major constituents of microbial communities that constructed the microbialites have long been disputed. Our new study describes morphological features, growth direction and reproduction characteristic of columnar microfossils obtained from the microbialites, and all characteristics indicate that these microfossils are assignable to a type of photosynthesizing bacteria, known as Pleurocapsales cyanobacteria. Both biomineralization and dolomitization of these Pleurocapsales are evaluated based on in‐situ observations and geochemical analyses. The new results show that the cluster‐branching morphologies, together with common occurrence and strong calcification capacity indicate that Pleurocapsales were key constructors of the microbialites. High Mg/(Mg + Ca) ratios coinciding with the microbialites and Mg‐enrichment in the microfossils suggest that the Pleurocapsales may have catalyzed dolomitization of the microbialites after the end‐Permian mass extinction.
Article
In view of the strong hydrophilicity of malachite, the sulfidation performance of conventional sulphidizing reagent sodium sulfide on malachite is not satisfactory. In this work, we discussed the effect of tetraamminecopper (II) complex pretreatment on the sulfidation and flotation behavior of malachite. The performance was evaluated by micro-flotation experiments. The flotation results showed that a better flotation recovery can be obtained with a molar concentration of tetraamminecopper (II) sulfate of only one-twentieth of the conventional activator (NH4)2SO4, all else being equal. Scanning Electron Microscope with Energy Dispersive Spectrometer (SEM-EDS) shows that the weight percentage of S and Cu on the surface of the sulfidized malachite increased significantly in the present of [Cu(NH3)4]²⁺. The FTIR and Raman results showed that sulfur ions could be chemisorbed on the surface of malachite and form a layer of copper-sulfide species. X-ray photoelectron spectroscopy (XPS) further confirmed the actual existence of the sulfide layer, which consists of monosulfide (S²⁻), disulfide(S2²⁻) and polysulfide (Sn²⁻). The presence of the activator [Cu(NH3)4]²⁺ can significantly increase the formation of disulfide and polysulfide on the surface of malachite, thereby promoting the subsequent interfacial adsorption of xanthate.
Thesis
Calcareous biominerals present a great variety of forms and biological functions, but also a number of common structural features. In particular, they appear, in their great majority, to be formed by an assembly of spheroidal crystalline nanoparticles, while having crystalline properties close to those of a single crystal. The compactness of this nanostructure suggests the existence of a liquid transient prior to the formation of an amorphous state, which has been evidenced in a number of cases. The crystallisation pathway, which would involve intermediate states typical of so-called non-classical crystallisation processes, is not yet fully established. In particular, the existence of an ion-enriched liquid phase remains complex to demonstrate in vivo. In order to assess the relevance of such a hypothesis, an approach based on a synthetic model including a dense liquid phase was used. Amorphous calcium carbonate films of sub-micron thickness were produced by CO₂ gas diffusion in a calcium solution in the presence of anionic polyelectrolyte. The mechanism of film formation, combining the development of a 2D pattern by liquid-liquid phase separation and the irreversible aggregation of amorphous nanoparticles formed in solution, was demonstrated. The amorphous films were crystallized by heating, exposure to controlled relative humidity, or aging in the reaction medium. The characterization of these 2D crystals, in particular by Bragg ptychography, has made it possible to describe the amorphous-crystal transition mechanisms and to specify the crystalline properties for each crystallization condition. Some crystals show properties very similar to biogenic crystals, thus supporting the hypothesis of a liquid intermediate in calcareous biomineralization.
Article
Full-text available
A methodological proposal for the characterisation of dolerite rock aiming to test a non-destructive and non-invasive analytical approach has been developed. Geological samples were collected from several natural outcrops and studied together with seven archaeological stone tools found in a Chalcolithic site of the southern Valencian Community (Spain). The samples were analysed employing portable energy dispersive X-ray fluorescence spectroscopy, Raman microspectroscopy and Fourier transform near infrared spectroscopy. The obtained data were statistically processed in order to evaluate affinities and differences among the geologic outcrops and to evaluate the possible provenance of the stone tools. The results of the different techniques were compared and evaluated. The three techniques showed results that were in most of the cases consistent one with each other, suggesting that combining multielement analysis and Raman could be a good way to identify stone tools raw material procurement being the prior step for the reconstruction of ancient exchange networks.
Article
Full-text available
NASA's Mars 2020 and ESA's ExoMars will collect Raman measurements in dusty field conditions obscuring underlying rocks. This presents a challenge for remote Raman measurements at distances where mechanical or ablative sample cleaning is not straightforward. Historically, probing broad lithostratigraphic suites has been thwarted by the need for pristine targets and high‐quality spectra. We provide a means of identifying Raman spectra of common rock‐forming silicate, carbonate, and sulfate minerals under low signal‐to‐noise‐ratios, Mars‐like conditions using a convolutional neural network (CNN). The CNN was trained on the Machine Learning Raman Open Data set data set with 500,000+ Raman spectra of hand samples/powder mixtures (5,000+ spectra/mineral class). Diversity in sample microtopography, orientation, and crystallinity simulated varying laser focuses and spectral quality, and no traditional spectral preprocessing such as cosmic ray or baseline removal was employed. The CNN identified low‐intensity Raman scatterers (micas and amphiboles), mixed minerals, and distinguished between mineral endmembers with +99% success. We present among the first known implementations of “big data” machine learning using varied, high‐volume Raman spectral datasets. The pattern recognition abilities of CNNs can facilitate scientist Raman spectral interpretation on Earth and autonomous rover decision‐making on planets like Mars; increasing scientific yield, correcting human classification errors, reducing the need for thorough target dust removal during evaluative measurements, and streamlining the data communications pipeline—saving time and resources. This study examines an end‐to‐end development process for creating a deep learning algorithm sensitive to varieties of Raman spectra and provides guidelines for CNN model development at the interface of Raman spectroscopy, deep learning, and planetary science.
Article
Full-text available
Raman spectra are reported for biogenic carbonates from a scleractinian coral (Porites sp.), pink pigmented (Corallium regale) and unpigmented (Corallium secundum) precious corals, and natural and cultured pearls. Spectra of aragonitic Porites coral and pearls show Raman bands typical of aragonite. Spectra of the deep-sea, precious corals closely resemble Raman spectra of magnesian calcite, with the exception of the pink coral, which shows seven additional bands in the spectral region of 1020-3758 cm-1. Positional disordering of carbonate ions in biogenic magnesian calcite may affect the relative stabilities of these carbonates as they undergo diagenesis. -from Authors
Chapter
Origin of Molecular Spectra Origin of Infrared and Raman Spectra Vibration of a Diatomic Molecule Normal Coordinates and Normal Vibrations Symmetry Elements and Point Groups Symmetry of Normal Vibrations and Selection Rules Introduction to Group Theory The Number of Normal Vibrations for Each Species Internal Coordinates Selection Rules for Infrared and Raman Spectra Structure Determination Principle of the GF Matrix Method Utilization of Symmetry Properties Potential Fields and Force Constants Solution of the Secular Equation Vibrational Frequencies of Isotopic Molecules Metal–Isotope Spectroscopy Group Frequencies and Band Assignments Intensity of Infrared Absorption Depolarization of Raman Lines Intensity of Raman Scattering Principle of Resonance Raman Spectroscopy Resonance Raman Spectra Theoretical Calculation of Vibrational Frequencies Vibrational Spectra in Gaseous Phase and Inert Gas Matrices Matrix Cocondensation Reactions Symmetry in Crystals Vibrational Analysis of Crystals The Correlation Method Lattice Vibrations Polarized Spectra of Single Crystals Vibrational Analysis of Ceramic Superconductors References
Article
6. Summary The Raman spectra of the three crystals are recorded using the λ 2536·5 radiation of mercury and eleven new lines of low intensity are reported. These include the appearance in the cases of SrCO3 and BaCO3 of the line corresponding to the Raman-inactive mode of the free-ion, this line being of progressively diminishing intensity in the three cases owing to the structures progressively approaching that of hexagonal symmetry. The similarities and the differences observed in the three spectra are also correlated with the details of the crystal structures.
Article
Equilibrium structures of Li2CO3 and K2CO3 were calculated using ab initio molecular orbital calculations carried out at the Hartree-Fock (HF) level. Of the four structures considered for Li2CO3 and K2CO3, the most stable was a structure with all five atoms in a plane. The harmonic frequencies were also calculated and found to be in agreement with the present Raman measurements. Structure factors, calculated from the ab initio data for each of the four structures considered, are compared with existing X-ray results.
Article
The Raman and mid-range infrared spectra have been measured on natural limestone and dolomite minerals. The carbonate minerals show four prominent absorption bands in the regions 1450–1420, 890–870, 720–700 and 1000–1100 cm−1. The positions of the wavenumbers are unique for each carbonate mineral and are thus diagnostic of their mineralogy. Calcite and dolomite groups are characterized by the Raman wavenumbers at 288 and 309 cm−1 and the infrared absorption bands at 712 and 728 cm−1, respectively. The principal wavenumber at 1092 cm−1 in the limestone spectra is accompanied by two satellites with values of 1062 and 1075 cm−1. The observed non-split peaks ν2 and ν4 in the infrared spectra of limestone indicate the presence of calcite structure in all these samples. The principal reflections occurring at the d-spacings, 3.03482, 1.91658 and 1.87962 Å, confirm the presence of calcite structure in limestone minerals. The principal reflections occurring at the d-spacings, 3.037, 1.79179 and 2.19750 Å, confirm the existence of dolomite structure in the dolomite minerals. The calculated lattice parameters for the limestone minerals are: a = 4.9781 Å, c = 17.1188 Å and V = 367.392(Å)3 and the corresponding values for the dolomite minerals are: a = 4.8247 Å, c = 15.9868 Å and V = 322.28 (Å)3. Copyright © 2006 John Wiley & Sons, Ltd.
Article
Azurite is a basic copper carbonate pigment largely employed in painting realization. The areas painted with azurite are easily alterable and are often less resistant than the other parts of artworks. The azurite alteration in a black pigment, the copper oxide (tenorite), has been studied by micro-Raman spectroscopy. The blackening can be due to thermal or chemical alterations: in the second case the alterations being due to the presence of alkaline conditions. Laser-induced degradation of azurite has been studied as a function of the grain size. The results show that the temperature of the grains decreases as the size increases, and azurite degrades into tenorite only below the critical value of 25 µm. To study the chemical alteration of azurite, the pigment has been applied on the plaster of terracotta samples and analyzed at different pH values by micro-Raman spectroscopy. As opposed to most part of the analytical techniques, it can detect the presence of both azurite and tenorite molecules in the same micro areas, and provides a valuable tool to determine azurite degradation. Copyright © 2008 John Wiley & Sons, Ltd.
Chapter
Inorganic molecules (ions) and ligands are classified into diatomic, triatomic, four-atomic, five-atomic, six-atomic, and seven-atomic types, and their normal modes of vibration are illustrated and the corresponding vibrational frequencies are listed for each type. Molecules of other types are grouped into compounds of boron, carbon, silicon, nitrogen, phosphorus, and sulfur, and the structures and infrared (IR)/Raman spectra of select examples are shown for each group. Group frequency charts including band assignments are shown for phosphorus and sulfur compounds. Other group frequency charts include hydrogen stretching frequencies, halogen stretching frequencies, oxygen stretching and bending frequencies, inorganic ions, and metal complexes containing simple coordinating ligands.