Infrared and Raman Spectroscopic Charact
Transition Met Chem (2012) 37:777–782
DOI 10.1007/s11243-012-9652-x
Infrared and Raman spectroscopic characterization
of the phosphate mineral kosnarite KZr2(PO4)3 in comparison
with other pegmatitic phosphates
Ray L. Frost • Yunfei Xi • Ricardo Scholz
Fernanda M. Belotti
•
Received: 22 August 2012 / Accepted: 24 September 2012 / Published online: 4 October 2012
Ó Springer Science+Business Media Dordrecht 2012
Abstract In this research, we have used vibrational
spectroscopy to study the phosphate mineral kosnarite
KZr2(PO4)3. Interest in this mineral rests with the ability of
zirconium phosphates (ZP) to lock in radioactive elements.
ZP have the capacity to concentrate and immobilize the
actinide fraction of radioactive phases in homogeneous
zirconium phosphate phases. The Raman spectrum of
kosnarite is characterized by a very intense band at
1,026 cm-1 assigned to the symmetric stretching vibration
of the PO43- m1 symmetric stretching vibration. The series
of bands at 561, 595 and 638 cm-1 are assigned to the m4
out-of-plane bending modes of the PO43- units. The
intense band at 437 cm-1 with other bands of lower
wavenumber at 387, 405 and 421 cm-1 is assigned to the
m2 in-plane bending modes of the PO43- units. The number
of bands in the antisymmetric stretching region supports
the concept that the symmetry of the phosphate anion in the
kosnarite structure is preserved. The width of the infrared
spectral profile and its complexity in contrast to the wellElectronic supplementary material The online version of this
article (doi:10.1007/s11243-012-9652-x) contains supplementary
material, which is available to authorized users.
R. L. Frost (&) Y. Xi
Science and Engineering Faculty, School of Chemistry, Physics
and Mechanical Engineering, Queensland University of
Technology, GPO Box 2434, Brisbane, QLD 4001, Australia
e-mail: [email protected]
R. Scholz
Geology Department, School of Mines, Federal University
of Ouro Preto, Campus Morro do Cruzeiro, Ouro Preto,
MG 35,400-00, Brazil
F. M. Belotti
Federal University of Itajuba´, Campus Itabira, Itabira,
MG 35,903-087, Brazil
resolved Raman spectrum show that the pegmatitic phosphates are better studied with Raman spectroscopy.
Introduction
Kosnarite is a pegmatitic phosphate of formula KZr2(PO4)3.
The colour is variable and can be colourless, pale blue to pale
green and orange. Other natural minerals related to kosnarite
and their structure have been reported [1, 2]. The mineral is
found in several regions worldwide including the type locality
in Mt Mica, near Paris, Maine USA, in the Black Mountain
quarry, Maine USA, at Wycheproof, Victoria, Australia, and
at Jenipapo district, Itinga, Brazil. The mineral is hexagonal–
pseudocubic [3, 4]. The cell data are space group R3 barc with
a = 8.687 and c = 23.877 with Z = 6 [5].
It is interesting that the synthesis of analogues with a
kosnarite structure has been forthcoming [3]. However, no
spectroscopic measurements have been undertaken. Other
natural minerals with a kosnarite structure, namely wycheproofite, have been reported [1]. The crystal structure of
wycheproofite has been elucidated [6]. Another zirconium
phosphate mineral is selwynite [2]. The reason why there is
strong interest in the formation of zirconium phosphates [7]
and rare earth phosphates is that these minerals can be used to
lock in radioactive elements [8]. Synthetic orthophosphates
are analogues of the natural mineral kosnarite that exhibits a
wide range of distinctive physical and chemical properties
including a tendency to wide isomorphism [9]. The presence
of U, Np and Pu actinides (IV) of the total NZP crystalline
modifications formulas KZr2(PO4)3 brings together the
crystal chemistry of the d- and f-elements to some extent.
The knowledge of the crystal structures of kosnarite and
related synthetic inorganic phases is important for better
understanding the genesis of uranium deposits, interaction
123
778
of uranium mine and mill tailings with the environment,
actinide transport in soils and the vadose zones and the
performance of geological repositories for nuclear waste.
Uranyl minerals are also observed as products of alteration
(hydration–oxidation weathering) of spent nuclear fuel.
Phosphate minerals exhibit considerable structural and
chemical diversity and reflect geochemical conditions
dominant during their formation. Uranyl oxide hydrates,
such as the studied uranyl minerals, schoepite, becquerelite, billietite, curite and vandendriescheite, may be understood especially as weathering products of uraninite in the
oxidized zone of uranium deposits. This suggests the possibility of concentration and immobilization of the actinide
fraction of radioactive phases in homogeneous NZP phases
[9]. The synthesis and crystal chemistry of phosphates
containing the actinide elements offers a mechanism for the
capture and immobilization of radioactive nuclides [10].
In this work, samples of a pure, monomineral kosnarite
from the Jenipapo pegmatite district, located in the
municipality of Itinga, Minas Gerais, Brazil, were analysed. Studies include spectroscopic characterization of the
structure with infrared and Raman spectroscopy. To support the mineral characterization, chemical analysis via
electron microprobe analysis in the WDS mode (EMP) and
using a scanning electron microscope was carried out.
Geological setting, occurrence and general appearance
The studied samples were collected from a granitic pegmatite in the Jenipapo district, located in the Piauı´ valley,
municipality of Itinga. The region is well-known as an
important source of rare phosphates and gemological
minerals. The pegmatite is located in the Arac¸uaı´ pegmatite
district, one of the subdivisions of the Eastern Brazilian
Pegmatite province (EBP) [11]. The Arac¸uaı´ pegmatite
district covers an area of about 10,000 km2, in the northern
region of Minas Gerais, in the Jequitinhonha River basin,
about 560 km north of Belo Horizonte.
The pegmatite is heterogeneous with well-developed
mineralogical and textural zoning. The pegmatite is hosted by
cordierite–biotite–quartz schists with minor intercalations of
calcsilicate rocks of the Salinas Formation. Tourmalinization
is observed in the contact between the pegmatite and the host
rock. Hydrothermal and metasomatic fluids were responsible
for the development of miarolitic cavities. Primary phosphates
were not observed. The primary mineral association is represented by quartz, muscovite, microcline, schorl and
almandine–spessartine. The secondary association is mainly
composed by albite, Li-bearing micas, cassiterite, elbaite and
hydrothermal rose quartz. In the Jenipapo pegmatite district,
secondary phosphates, namely eosphorite, fluorapatite, zanazziite, montebrasite and ushkovite, occur in miarolitic
123
Transition Met Chem (2012) 37:777–782
cavities in association with albite, quartz and muscovite.
Kosnarite grows usually along the surface of albite, muscovite
and montebrasite.
Experimental
Sample description and preparation
The kosnarite sample studied in this work was collected
from a granitic pegmatite in the Jenipapo district and was
incorporated in the collection of the Geology Department
of the Federal University of Ouro Preto, Minas Gerais,
Brazil, with sample code SAA-071. The crystals occur in
association with albite in miarolitic cavities.
The sample was gently crushed, and the associated
minerals were removed under a stereomicroscope Leica
MZ4. The kosnarite sample was phase-analysed by X-ray
diffraction. Electron microprobe and scanning electron
microscopy were applied to support the mineralogical
characterization.
Scanning electron microscopy (SEM)
Experiments and analyses involving electron microscopy
were performed in the Center of Microscopy of the Universidade Federal de Minas Gerais, Belo Horizonte, Minas
Gerais, Brazil (http://www.microscopia.ufmg.br).
Kosnarite crystals were coated with a 5 nm layer of
evaporated Au. Secondary electron and backscattered
electron images were obtained using a JEOL JSM-6360LV.
Qualitative and semi-quantitative chemical analysis in the
EDS mode was performed with a ThermoNORAN equipment model Quest and was applied to support the mineral
characterization.
Raman microprobe spectroscopy
Crystals of kosnarite were placed on a polished metal surface
on the stage of an Olympus BHSM microscope, equipped
with 109, 209 and 509 objectives. The microscope is part
of a Renishaw 1,000 Raman microscope system, which also
includes a monochromator, a filter system and a CCD
detector (1,024 pixels). The Raman spectra were excited by a
Spectra-Physics model 127 He–Ne laser producing highly
polarized light at 633 nm and collected at a nominal resolution of 2 cm-1 and a precision of ± 1 cm-1 in the range
between 200 and 4,000 cm-1. Repeated acquisitions on the
crystals using the highest magnification (509) were accumulated to improve the signal to noise ratio of the spectra.
Raman Spectra were calibrated using the 520.5 cm-1 line of
a silicon wafer. The Raman spectrum of at least 10 crystals
was collected to ensure the consistency of the spectra.
Transition Met Chem (2012) 37:777–782
The Raman spectrum of kosnarite is provided in the
RRUFF data base [see http://rruff.info/kosnarite/display=
default/]. The origin of the kosnarite was from Jenipapo
District, Itinga, Minas Gerais, Brazil. No assignment of the
bands is given in the RRUFF data base. The spectra were
downloaded and are presented in the supplementary
information as Figures S1 to S4.
Infrared spectroscopy
Infrared spectra were obtained using a Nicolet Nexus 870
FTIR spectrometer with a smart endurance single bounce
diamond ATR cell. Spectra over the 4,000–525 cm-1 range
were obtained by the co-addition of 128 scans with a resolution of 4 cm-1 and a mirror velocity of 0.6329 cm/s. Spectra
were co-added to improve the signal to noise ratio. The
infrared spectra are given in the supplementary information.
Spectral manipulation such as baseline correction/
adjustment and smoothing were performed using the
Spectracalc software package GRAMS (Galactic Industries
Corporation, NH, USA). Band component analysis was
undertaken using the Jandel ‘Peakfit’ software package that
enabled the type of fitting function to be selected and
allows specific parameters to be fixed or varied accordingly. Band fitting was done using a Lorentzian–Gaussian
cross-product function with the minimum number of
component bands used for the fitting process. The Lorentzian–Gaussian ratio was maintained at values[0.7, and
fitting was undertaken until reproducible results were
obtained with squared correlations of r2 [ 0.995.
Results and discussion
Chemical characterization
The SEM image of kosnarite sample studied in this work is
shown in Fig. 1. Kosnarite crystals show typical trigonal
rhombohedra form. Qualitative chemical composition
779
shows a pure and homogeneous Zr and K phosphate as
expected for kosnarite. A minor amount of Mg was also
observed.
Spectroscopy
It is obvious that there is minimal intensity in the bands in
the 2,600–4,000 cm-1 spectral range. This region is where
the OH stretching region occurs. The lack of intensity
supports the fact that there are no OH groups in the
structure of kosnarite. Some intensity may be due to
adsorbed water. The spectra are subdivided into subsections based upon the type of vibration being studied. Figure 2a displays the Raman spectrum of kosnarite over the
800–1,400 cm-1 spectral range. Figure 2b illustrates the
infrared spectrum expanded to the 500 to 1,300 cm-1
spectral range. In comparison, the infrared spectrum displays a broad spectral profile which may be decomposed
into component bands. In contrast, the Raman spectrum
shows quite well-resolved bands.
The Raman spectrum is characterized by a very intense
band at 1,026 cm-1 assigned to the symmetric stretching
vibration of the PO43- m1 symmetric stretching vibration.
Two bands at 1,063 and 1,088 cm-1 are attributed to the
PO43- m3 antisymmetric stretching vibration. Other low
intensity bands are also found at 1,116 and 1,149 cm-1
which are assigned to this vibration. The Raman spectra of
kosnarite given in Figures S1 and S2 show a very intense
band at 1,025 cm-1 with a shoulder at 1,020 cm-1. Raman
bands were also found at 1,062 and 1,088 cm-1. The position
of these bands is in good agreement with that reported in this
work. The infrared spectrum shows a broad spectral profile
which is attributed to the PO43- m3 antisymmetric stretching
modes. A sharp peak at 1,202 cm-1 is observed.
In some ways, the Raman spectrum of kosnarite does
show a resemblance to the spectrum of beryllonite
NaBePO4. The spectrum of beryllonite is dominated by a
single very sharp band at 1,011 cm-1. Often, the position
of the symmetric stretching mode at lower wavenumbers,
Fig. 1 a Backscattered electron
image (BSI) of a kosnarite
aggregate up to 1.0 mm in
length. b EDS analysis of
kosnarite
123
780
Transition Met Chem (2012) 37:777–782
Fig. 2 a Raman spectrum of
kosnarite over the 800 to
1,400 cm-1 spectral range
b Infrared spectrum of kosnarite
over the 500 to 1,300 cm-1
spectral range
Fig. 3 a Raman spectrum of
kosnarite over the 300 to
800 cm-1 spectral range
b Raman spectrum of kosnarite
over the 100 to 300 cm-1
spectral range
for example, the band position for lithiophilite LiMnPO4,
occurs at 950 cm-1. The position of the band seems to be a
function of the cation size. This band is assigned to the m1
PO43- symmetric stretching vibration. Another pegmatitic
phosphate is hureaulite (MnFe)5(PO4)2-(HPO4)24(H2O).
123
The Raman spectrum of hureaulite is noteworthy for a very
intense band at 950 cm-1 which is assigned to the HPO42PO stretching vibrations. This band has a shoulder at
941 cm-1. This band is given the same assignment, the
implication of which is that all the hydrogen phosphate
Transition Met Chem (2012) 37:777–782
781
Fig. 4 a Raman spectrum of kosnarite over the 2,600 to 4,000 cm-1 spectral range b Infrared spectrum of kosnarite over the 2,600 to
4,000 cm-1 spectral range
units are not equivalent. A low intensity Raman band is
found at 989 cm-1 and is assigned to the phosphate PO43symmetric stretching vibration.
The series of bands at 1,046, 1,053 and 1,068 cm-1 of
kosnarite are attributed to the m3 PO43- antisymmetric
stretching vibration. For pegmatitic phosphates, often the
spectrum of the PO43- stretching region is complex with
quite a number of phosphate bands which are assigned to
the presence of not only PO43- but also HOPO32- units. In
the case of the Raman spectrum of kosnarite and beryllonite, the spectrum of the PO43- spectral region is simple,
thus indicating that the phosphate anion symmetry is
maintained. It would appear that if the pegmatitic phosphate contains water or OH groups, then the likelihood of
HOPO32- unit formation increases and the complexity of
the phosphate stretching bands increases.
The Raman spectra of kosnarite in the 300 to 800 cm-1
and in the 100 to 300 cm-1 region are reported in Fig. 3a,
b. The series of bands at 561, 595 and 638 cm-1 are
assigned to the m4 out-of-plane bending modes of the PO43units. The intense band at 437 cm-1 with other bands of
lower wavenumber at 387, 405 and 421 cm-1 is assigned
to the m2 in-plane bending modes of the PO43- units. In
comparison, the Raman spectrum of beryllonite is more
complex. A significant number of bands in the Raman
spectrum of beryllonite in the 522 to 612 cm-1 are
assigned to the m4 out-of-plane bending modes of the PO43-
units. The lesser number of bands in the Raman spectrum
of kosnarite seems to indicate the preservation of the
symmetry of the PO43- anion. The Raman spectrum of
kosnarite given in the RRUFF data base seems to show a
lack of signal; nevertheless, Raman bands are noted at 523,
593 and 636 cm-1 in good agreement with the position of
bands reported in this work. Raman bands were observed at
420 and 437 cm-1 in harmony with the position of the
Raman bands reported in this work. The Raman peaks at
263, 290 and 318 cm-1 may be associated with metal–
oxygen stretching vibrations. The other bands at 122, 156
and 175 cm-1 are simply described as lattice vibrations.
The Raman spectrum of kosnarite in the 2,600 to
3,200 cm-1 spectral range is reported in Fig. 4a. These
bands are ascribed to an organic impurity on the surface of
the kosnarite. The infrared spectrum of kosnarite in the
2,800 to 4,000 cm-1 region is shown in Fig. 4b. The
spectrum is of a very low intensity and suffers from a lack
of signal. Nevertheless, infrared bands are found at 3,153,
3,285, 3,474 and 3,722 cm-1 and may be attributed to
water stretching vibrations of adsorbed water.
Conclusions
We have characterized the mineral kosnarite using vibrational spectroscopic techniques. A comparison is made with
123
782
the Raman spectrum of kosnarite from the RRUFF data base.
A comparison is also made with the Raman spectrum of
beryllonite. The mineral is characterized by an intense sharp
Raman band at 1,026 cm-1, assigned to the PO43- symmetric stretching mode. Raman bands at 1,060 and
1,088 cm-1 are attributed to the PO43- antisymmetric
stretching vibrations. The number of bands in the antisymmetric stretching region supports the concept that the symmetry of the phosphate anion in the kosnarite structure is
preserved. This concept is supported by the number of bands
found in the out-of-plane bending region. Multiple bands are
also found in the in-plane bending region with Raman bands
at 405, 421 and 437 cm-1. Strong Raman bands at 263, 290
and 318 cm-1 are attributed to metal oxygen vibrations.
Bands in the Raman spectrum are narrow and wellresolved in comparison with the infrared spectrum where a
complex spectral profile may be resolved into component
bands. We conclude from this that the pegmatitic phosphate minerals such as kosnarite are more readily studied
by Raman spectroscopy.
Acknowledgments The financial and infra-structure support of the
Discipline of Nanotechnology and Molecular Science, Science and
Engineering Faculty of the Queensland University of Technology is
gratefully acknowledged. The Australian Research Council (ARC) is
thanked for funding the instrumentation. The authors would like to
acknowledge the Center of Microscopy at the Universidade Federal
de Minas Gerais (http://www.microscopia.ufmg.br) for providing the
equipment and technical support for experiments involving electron
123
Transition Met Chem (2012) 37:777–782
microscopy. R. Scholz offers thanks to FAPEMIG–Fundac¸a˜o de
Amparo a` Pesquisa do estado de Minas Gerais (grant No. CRA–APQ03998-10).
References
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58:635–639
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4. Pet’kov VI, Shchelokov IA, Kurazhkovskaya VS, Orekhova NV,
Ermilova MM, Tereshchenko GF (2008) Zh Neorg Khim
53:1073–1080
5. Brownfield ME, Foord EE, Sutley SJ, Botinelly T (1993) Am
Mineral 78:653–656
6. Kolitsch U (2003) Euro J Mineral 15:1029–1034
7. Sukhanov MV, Pet’kov VI, Firsov DV, Kurazhkovskaya VS,
Borovikova EY (2011) Russ J Inorg Chem 56:1351–1357
8. Zaripov AR, Slunchev OM, Shmakova MG, Orlova VA, Galuzin
DD, Rovny SI, Asabina YA, Pet’kov VI (2007) Voprosy Radiatsionnoi Bezopasnosti: 28–35
9. Tomilin SV, Orlova AI, Lukinykh AN, Lizin AA (2006) Special
Publ Royal Soc Chem 305:421–423
10. Orlova AI, Kitaev DB, Kemenov DV, Orlova MP, Kazantsev
GN, Samoilov SG, Kurazhkovskaya VS (2003) Radiochemistry
(Moscow, Russian Federation) 45: 103–109
11. Pedrosa-Soares AC, Campos CMD, Noce CM, Silva LCD, Novo
TA, Roncato J, Medeiros SM, Castan˜eda C, Queiroga GN, Dantas
E, Dussin IA, Alkmim F (2011) Geological Society. Special
Publication 350: 25
DOI 10.1007/s11243-012-9652-x
Infrared and Raman spectroscopic characterization
of the phosphate mineral kosnarite KZr2(PO4)3 in comparison
with other pegmatitic phosphates
Ray L. Frost • Yunfei Xi • Ricardo Scholz
Fernanda M. Belotti
•
Received: 22 August 2012 / Accepted: 24 September 2012 / Published online: 4 October 2012
Ó Springer Science+Business Media Dordrecht 2012
Abstract In this research, we have used vibrational
spectroscopy to study the phosphate mineral kosnarite
KZr2(PO4)3. Interest in this mineral rests with the ability of
zirconium phosphates (ZP) to lock in radioactive elements.
ZP have the capacity to concentrate and immobilize the
actinide fraction of radioactive phases in homogeneous
zirconium phosphate phases. The Raman spectrum of
kosnarite is characterized by a very intense band at
1,026 cm-1 assigned to the symmetric stretching vibration
of the PO43- m1 symmetric stretching vibration. The series
of bands at 561, 595 and 638 cm-1 are assigned to the m4
out-of-plane bending modes of the PO43- units. The
intense band at 437 cm-1 with other bands of lower
wavenumber at 387, 405 and 421 cm-1 is assigned to the
m2 in-plane bending modes of the PO43- units. The number
of bands in the antisymmetric stretching region supports
the concept that the symmetry of the phosphate anion in the
kosnarite structure is preserved. The width of the infrared
spectral profile and its complexity in contrast to the wellElectronic supplementary material The online version of this
article (doi:10.1007/s11243-012-9652-x) contains supplementary
material, which is available to authorized users.
R. L. Frost (&) Y. Xi
Science and Engineering Faculty, School of Chemistry, Physics
and Mechanical Engineering, Queensland University of
Technology, GPO Box 2434, Brisbane, QLD 4001, Australia
e-mail: [email protected]
R. Scholz
Geology Department, School of Mines, Federal University
of Ouro Preto, Campus Morro do Cruzeiro, Ouro Preto,
MG 35,400-00, Brazil
F. M. Belotti
Federal University of Itajuba´, Campus Itabira, Itabira,
MG 35,903-087, Brazil
resolved Raman spectrum show that the pegmatitic phosphates are better studied with Raman spectroscopy.
Introduction
Kosnarite is a pegmatitic phosphate of formula KZr2(PO4)3.
The colour is variable and can be colourless, pale blue to pale
green and orange. Other natural minerals related to kosnarite
and their structure have been reported [1, 2]. The mineral is
found in several regions worldwide including the type locality
in Mt Mica, near Paris, Maine USA, in the Black Mountain
quarry, Maine USA, at Wycheproof, Victoria, Australia, and
at Jenipapo district, Itinga, Brazil. The mineral is hexagonal–
pseudocubic [3, 4]. The cell data are space group R3 barc with
a = 8.687 and c = 23.877 with Z = 6 [5].
It is interesting that the synthesis of analogues with a
kosnarite structure has been forthcoming [3]. However, no
spectroscopic measurements have been undertaken. Other
natural minerals with a kosnarite structure, namely wycheproofite, have been reported [1]. The crystal structure of
wycheproofite has been elucidated [6]. Another zirconium
phosphate mineral is selwynite [2]. The reason why there is
strong interest in the formation of zirconium phosphates [7]
and rare earth phosphates is that these minerals can be used to
lock in radioactive elements [8]. Synthetic orthophosphates
are analogues of the natural mineral kosnarite that exhibits a
wide range of distinctive physical and chemical properties
including a tendency to wide isomorphism [9]. The presence
of U, Np and Pu actinides (IV) of the total NZP crystalline
modifications formulas KZr2(PO4)3 brings together the
crystal chemistry of the d- and f-elements to some extent.
The knowledge of the crystal structures of kosnarite and
related synthetic inorganic phases is important for better
understanding the genesis of uranium deposits, interaction
123
778
of uranium mine and mill tailings with the environment,
actinide transport in soils and the vadose zones and the
performance of geological repositories for nuclear waste.
Uranyl minerals are also observed as products of alteration
(hydration–oxidation weathering) of spent nuclear fuel.
Phosphate minerals exhibit considerable structural and
chemical diversity and reflect geochemical conditions
dominant during their formation. Uranyl oxide hydrates,
such as the studied uranyl minerals, schoepite, becquerelite, billietite, curite and vandendriescheite, may be understood especially as weathering products of uraninite in the
oxidized zone of uranium deposits. This suggests the possibility of concentration and immobilization of the actinide
fraction of radioactive phases in homogeneous NZP phases
[9]. The synthesis and crystal chemistry of phosphates
containing the actinide elements offers a mechanism for the
capture and immobilization of radioactive nuclides [10].
In this work, samples of a pure, monomineral kosnarite
from the Jenipapo pegmatite district, located in the
municipality of Itinga, Minas Gerais, Brazil, were analysed. Studies include spectroscopic characterization of the
structure with infrared and Raman spectroscopy. To support the mineral characterization, chemical analysis via
electron microprobe analysis in the WDS mode (EMP) and
using a scanning electron microscope was carried out.
Geological setting, occurrence and general appearance
The studied samples were collected from a granitic pegmatite in the Jenipapo district, located in the Piauı´ valley,
municipality of Itinga. The region is well-known as an
important source of rare phosphates and gemological
minerals. The pegmatite is located in the Arac¸uaı´ pegmatite
district, one of the subdivisions of the Eastern Brazilian
Pegmatite province (EBP) [11]. The Arac¸uaı´ pegmatite
district covers an area of about 10,000 km2, in the northern
region of Minas Gerais, in the Jequitinhonha River basin,
about 560 km north of Belo Horizonte.
The pegmatite is heterogeneous with well-developed
mineralogical and textural zoning. The pegmatite is hosted by
cordierite–biotite–quartz schists with minor intercalations of
calcsilicate rocks of the Salinas Formation. Tourmalinization
is observed in the contact between the pegmatite and the host
rock. Hydrothermal and metasomatic fluids were responsible
for the development of miarolitic cavities. Primary phosphates
were not observed. The primary mineral association is represented by quartz, muscovite, microcline, schorl and
almandine–spessartine. The secondary association is mainly
composed by albite, Li-bearing micas, cassiterite, elbaite and
hydrothermal rose quartz. In the Jenipapo pegmatite district,
secondary phosphates, namely eosphorite, fluorapatite, zanazziite, montebrasite and ushkovite, occur in miarolitic
123
Transition Met Chem (2012) 37:777–782
cavities in association with albite, quartz and muscovite.
Kosnarite grows usually along the surface of albite, muscovite
and montebrasite.
Experimental
Sample description and preparation
The kosnarite sample studied in this work was collected
from a granitic pegmatite in the Jenipapo district and was
incorporated in the collection of the Geology Department
of the Federal University of Ouro Preto, Minas Gerais,
Brazil, with sample code SAA-071. The crystals occur in
association with albite in miarolitic cavities.
The sample was gently crushed, and the associated
minerals were removed under a stereomicroscope Leica
MZ4. The kosnarite sample was phase-analysed by X-ray
diffraction. Electron microprobe and scanning electron
microscopy were applied to support the mineralogical
characterization.
Scanning electron microscopy (SEM)
Experiments and analyses involving electron microscopy
were performed in the Center of Microscopy of the Universidade Federal de Minas Gerais, Belo Horizonte, Minas
Gerais, Brazil (http://www.microscopia.ufmg.br).
Kosnarite crystals were coated with a 5 nm layer of
evaporated Au. Secondary electron and backscattered
electron images were obtained using a JEOL JSM-6360LV.
Qualitative and semi-quantitative chemical analysis in the
EDS mode was performed with a ThermoNORAN equipment model Quest and was applied to support the mineral
characterization.
Raman microprobe spectroscopy
Crystals of kosnarite were placed on a polished metal surface
on the stage of an Olympus BHSM microscope, equipped
with 109, 209 and 509 objectives. The microscope is part
of a Renishaw 1,000 Raman microscope system, which also
includes a monochromator, a filter system and a CCD
detector (1,024 pixels). The Raman spectra were excited by a
Spectra-Physics model 127 He–Ne laser producing highly
polarized light at 633 nm and collected at a nominal resolution of 2 cm-1 and a precision of ± 1 cm-1 in the range
between 200 and 4,000 cm-1. Repeated acquisitions on the
crystals using the highest magnification (509) were accumulated to improve the signal to noise ratio of the spectra.
Raman Spectra were calibrated using the 520.5 cm-1 line of
a silicon wafer. The Raman spectrum of at least 10 crystals
was collected to ensure the consistency of the spectra.
Transition Met Chem (2012) 37:777–782
The Raman spectrum of kosnarite is provided in the
RRUFF data base [see http://rruff.info/kosnarite/display=
default/]. The origin of the kosnarite was from Jenipapo
District, Itinga, Minas Gerais, Brazil. No assignment of the
bands is given in the RRUFF data base. The spectra were
downloaded and are presented in the supplementary
information as Figures S1 to S4.
Infrared spectroscopy
Infrared spectra were obtained using a Nicolet Nexus 870
FTIR spectrometer with a smart endurance single bounce
diamond ATR cell. Spectra over the 4,000–525 cm-1 range
were obtained by the co-addition of 128 scans with a resolution of 4 cm-1 and a mirror velocity of 0.6329 cm/s. Spectra
were co-added to improve the signal to noise ratio. The
infrared spectra are given in the supplementary information.
Spectral manipulation such as baseline correction/
adjustment and smoothing were performed using the
Spectracalc software package GRAMS (Galactic Industries
Corporation, NH, USA). Band component analysis was
undertaken using the Jandel ‘Peakfit’ software package that
enabled the type of fitting function to be selected and
allows specific parameters to be fixed or varied accordingly. Band fitting was done using a Lorentzian–Gaussian
cross-product function with the minimum number of
component bands used for the fitting process. The Lorentzian–Gaussian ratio was maintained at values[0.7, and
fitting was undertaken until reproducible results were
obtained with squared correlations of r2 [ 0.995.
Results and discussion
Chemical characterization
The SEM image of kosnarite sample studied in this work is
shown in Fig. 1. Kosnarite crystals show typical trigonal
rhombohedra form. Qualitative chemical composition
779
shows a pure and homogeneous Zr and K phosphate as
expected for kosnarite. A minor amount of Mg was also
observed.
Spectroscopy
It is obvious that there is minimal intensity in the bands in
the 2,600–4,000 cm-1 spectral range. This region is where
the OH stretching region occurs. The lack of intensity
supports the fact that there are no OH groups in the
structure of kosnarite. Some intensity may be due to
adsorbed water. The spectra are subdivided into subsections based upon the type of vibration being studied. Figure 2a displays the Raman spectrum of kosnarite over the
800–1,400 cm-1 spectral range. Figure 2b illustrates the
infrared spectrum expanded to the 500 to 1,300 cm-1
spectral range. In comparison, the infrared spectrum displays a broad spectral profile which may be decomposed
into component bands. In contrast, the Raman spectrum
shows quite well-resolved bands.
The Raman spectrum is characterized by a very intense
band at 1,026 cm-1 assigned to the symmetric stretching
vibration of the PO43- m1 symmetric stretching vibration.
Two bands at 1,063 and 1,088 cm-1 are attributed to the
PO43- m3 antisymmetric stretching vibration. Other low
intensity bands are also found at 1,116 and 1,149 cm-1
which are assigned to this vibration. The Raman spectra of
kosnarite given in Figures S1 and S2 show a very intense
band at 1,025 cm-1 with a shoulder at 1,020 cm-1. Raman
bands were also found at 1,062 and 1,088 cm-1. The position
of these bands is in good agreement with that reported in this
work. The infrared spectrum shows a broad spectral profile
which is attributed to the PO43- m3 antisymmetric stretching
modes. A sharp peak at 1,202 cm-1 is observed.
In some ways, the Raman spectrum of kosnarite does
show a resemblance to the spectrum of beryllonite
NaBePO4. The spectrum of beryllonite is dominated by a
single very sharp band at 1,011 cm-1. Often, the position
of the symmetric stretching mode at lower wavenumbers,
Fig. 1 a Backscattered electron
image (BSI) of a kosnarite
aggregate up to 1.0 mm in
length. b EDS analysis of
kosnarite
123
780
Transition Met Chem (2012) 37:777–782
Fig. 2 a Raman spectrum of
kosnarite over the 800 to
1,400 cm-1 spectral range
b Infrared spectrum of kosnarite
over the 500 to 1,300 cm-1
spectral range
Fig. 3 a Raman spectrum of
kosnarite over the 300 to
800 cm-1 spectral range
b Raman spectrum of kosnarite
over the 100 to 300 cm-1
spectral range
for example, the band position for lithiophilite LiMnPO4,
occurs at 950 cm-1. The position of the band seems to be a
function of the cation size. This band is assigned to the m1
PO43- symmetric stretching vibration. Another pegmatitic
phosphate is hureaulite (MnFe)5(PO4)2-(HPO4)24(H2O).
123
The Raman spectrum of hureaulite is noteworthy for a very
intense band at 950 cm-1 which is assigned to the HPO42PO stretching vibrations. This band has a shoulder at
941 cm-1. This band is given the same assignment, the
implication of which is that all the hydrogen phosphate
Transition Met Chem (2012) 37:777–782
781
Fig. 4 a Raman spectrum of kosnarite over the 2,600 to 4,000 cm-1 spectral range b Infrared spectrum of kosnarite over the 2,600 to
4,000 cm-1 spectral range
units are not equivalent. A low intensity Raman band is
found at 989 cm-1 and is assigned to the phosphate PO43symmetric stretching vibration.
The series of bands at 1,046, 1,053 and 1,068 cm-1 of
kosnarite are attributed to the m3 PO43- antisymmetric
stretching vibration. For pegmatitic phosphates, often the
spectrum of the PO43- stretching region is complex with
quite a number of phosphate bands which are assigned to
the presence of not only PO43- but also HOPO32- units. In
the case of the Raman spectrum of kosnarite and beryllonite, the spectrum of the PO43- spectral region is simple,
thus indicating that the phosphate anion symmetry is
maintained. It would appear that if the pegmatitic phosphate contains water or OH groups, then the likelihood of
HOPO32- unit formation increases and the complexity of
the phosphate stretching bands increases.
The Raman spectra of kosnarite in the 300 to 800 cm-1
and in the 100 to 300 cm-1 region are reported in Fig. 3a,
b. The series of bands at 561, 595 and 638 cm-1 are
assigned to the m4 out-of-plane bending modes of the PO43units. The intense band at 437 cm-1 with other bands of
lower wavenumber at 387, 405 and 421 cm-1 is assigned
to the m2 in-plane bending modes of the PO43- units. In
comparison, the Raman spectrum of beryllonite is more
complex. A significant number of bands in the Raman
spectrum of beryllonite in the 522 to 612 cm-1 are
assigned to the m4 out-of-plane bending modes of the PO43-
units. The lesser number of bands in the Raman spectrum
of kosnarite seems to indicate the preservation of the
symmetry of the PO43- anion. The Raman spectrum of
kosnarite given in the RRUFF data base seems to show a
lack of signal; nevertheless, Raman bands are noted at 523,
593 and 636 cm-1 in good agreement with the position of
bands reported in this work. Raman bands were observed at
420 and 437 cm-1 in harmony with the position of the
Raman bands reported in this work. The Raman peaks at
263, 290 and 318 cm-1 may be associated with metal–
oxygen stretching vibrations. The other bands at 122, 156
and 175 cm-1 are simply described as lattice vibrations.
The Raman spectrum of kosnarite in the 2,600 to
3,200 cm-1 spectral range is reported in Fig. 4a. These
bands are ascribed to an organic impurity on the surface of
the kosnarite. The infrared spectrum of kosnarite in the
2,800 to 4,000 cm-1 region is shown in Fig. 4b. The
spectrum is of a very low intensity and suffers from a lack
of signal. Nevertheless, infrared bands are found at 3,153,
3,285, 3,474 and 3,722 cm-1 and may be attributed to
water stretching vibrations of adsorbed water.
Conclusions
We have characterized the mineral kosnarite using vibrational spectroscopic techniques. A comparison is made with
123
782
the Raman spectrum of kosnarite from the RRUFF data base.
A comparison is also made with the Raman spectrum of
beryllonite. The mineral is characterized by an intense sharp
Raman band at 1,026 cm-1, assigned to the PO43- symmetric stretching mode. Raman bands at 1,060 and
1,088 cm-1 are attributed to the PO43- antisymmetric
stretching vibrations. The number of bands in the antisymmetric stretching region supports the concept that the symmetry of the phosphate anion in the kosnarite structure is
preserved. This concept is supported by the number of bands
found in the out-of-plane bending region. Multiple bands are
also found in the in-plane bending region with Raman bands
at 405, 421 and 437 cm-1. Strong Raman bands at 263, 290
and 318 cm-1 are attributed to metal oxygen vibrations.
Bands in the Raman spectrum are narrow and wellresolved in comparison with the infrared spectrum where a
complex spectral profile may be resolved into component
bands. We conclude from this that the pegmatitic phosphate minerals such as kosnarite are more readily studied
by Raman spectroscopy.
Acknowledgments The financial and infra-structure support of the
Discipline of Nanotechnology and Molecular Science, Science and
Engineering Faculty of the Queensland University of Technology is
gratefully acknowledged. The Australian Research Council (ARC) is
thanked for funding the instrumentation. The authors would like to
acknowledge the Center of Microscopy at the Universidade Federal
de Minas Gerais (http://www.microscopia.ufmg.br) for providing the
equipment and technical support for experiments involving electron
123
Transition Met Chem (2012) 37:777–782
microscopy. R. Scholz offers thanks to FAPEMIG–Fundac¸a˜o de
Amparo a` Pesquisa do estado de Minas Gerais (grant No. CRA–APQ03998-10).
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