Thermal decomposition of humboldtine. A high resolution thermogravimetric and hot stage Raman spectroscopic study

Article abstract of DOI:10.1023/B:JTAN.0000017349.31035.dd

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. Humboldtine as the natural iron(II) oxalate mineral is a classic example. Thermogravimetry coupled to evolved gas mass spectrometry shows dehydration takes place in two steps at 130 and 141°C. Loss of the oxalate as carbon dioxide occurs at 312 and 332°C. Dehydration is readily followed by Raman microscopy in combination with a thermal stage and is observed by the loss of intensity of the OH stretching vibration at 3318 cm^-1. The application of infrared emission spectroscopy supports the results of the TG-MS. Three Raman bands are observed at 1470, 1465 and 1432 cm^-1 attributed the CO symmetric stretching mode. The observation of the three bands supports the concept of multiple iron(II) oxalate phases. The significance of this work rests with the ability of Raman spectroscopy to identify iron(II) oxalate which often occurs as a film on a host rock.

Full text of DOI:10.1023/B:JTAN.0000017349.31035.dd

Journal of Thermal Analysis and Calorimetry, Vol. 75 (2004) 277–291
THERMAL DECOMPOSITION OF HUMBOLDTINE
A high resolution thermogravimetric and hot stage Raman
spectroscopic study
R. L. Frost* and M. L. Weier
Inorganic Materials Research Program, Queensland University of Technology, 2 George Street,
Brisbane, GPO Box 2434, Queensland 4001, Australia
(Received April 9, 2003; in revised form 6 October 2003)
Abstract
Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the
formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices.
Humboldtine as the natural iron(II) oxalate mineral is a classic example. Thermogravimetry coupled
to evolved gas mass spectrometry shows dehydration takes place in two steps at 130 and 141°C.
Loss of the oxalate as carbon dioxide occurs at 312 and 332°C. Dehydration is readily followed by
Raman microscopy in combination with a thermal stage and is observed by the loss of intensity of
the OH stretching vibration at 3318 cm–1. The application of infrared emission spectroscopy sup-
ports the results of the TG–MS. Three Raman bands are observed at 1470, 1465 and 1432 cm–1 at-
tributed the CO symmetric stretching mode. The observation of the three bands supports the concept
of multiple iron(II) oxalate phases. The significance of this work rests with the ability of Raman
spectroscopy to identify iron(II) oxalate which often occurs as a film on a host rock.
Keywords: high resolution thermogravimetric analysis, hot stage Raman spectroscopy,
humboldtine, infrared emission spectroscopy, oxalate
Introduction
The presence of oxalates is widespread in nature. These minerals form as the result of
expulsion of heavy metals from fungi, lichens and plants [1–3]. The production of
simple organic acids such as oxalic and citric acids has profound implications for
metal speciation in biogeochemical cycles [4]. The metal complexing properties of
the acids are essential to the nutrition of fungi and lichens and affects the metal stabil-
ity and mobility in the environment [4]. Lichens and fungi produce the oxalates of
heavy metals as a mechanism for the removal of heavy metals from the plant [5].
Humboldtine was identified as a mineral many years ago [6] and its structure was de-
termined [7–9]. Stacking faults in iron(II) oxalates has been determined [10, 11].
*
Author for correspondence: E-mail: r.frost@qut.edu.au
1388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
© 2004 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

278
FROST, WEIER: HUMBOLDTINE
Recently Macnish and others identified intracellular calcium oxalate crystals in
Geraldton wax flowers (Chamelaucium uncinatum). These authors considered that the
complexation of the oxalic acid with calcium controlled the concentration of heavy
metals in the plant. Importantly the crystals were <1 micron in size and were very diffi-
cult to identify using techniques such as X-ray diffraction. Raman spectroscopy how-
ever proved useful for the analysis of the calcium oxalate. The presence of these oxa-
late crystals appears to have an effect similar to that found in cacti [12]. Among the
oxalates are the two calcium oxalates known as weddellite (the dihydrate) and
whewellite (monohydrate). Ca-oxalate exists in two well-described modifications: as
the more stable monoclinic monohydrate whewellite and the less stable tetragonal
dihydrate weddellite. Weddellite serves for lichens as a water absorbing and accumu-
lating substrate which transforms to whewellite when humidity drops. Such minerals
are important in human physiology as the minerals are found in urinary tracts [13, 14].
Many other divalent oxalates exist in nature. The magnesium based oxalate is known as
glushinskite [15, 16]. The copper oxalate is known as moolooite [2, 17] and the iron(II)
oxalate as humboldtine [6, 18]. These three oxalates are also the product of lichen
growth. Two natural univalent oxalates are known. These are the oxalates of sodium
and ammonium known as natroxalate and oxammite [19].
Indeed the presence of oxalates have been evidence for the deterioration of
works of art [20–22]. Carbon dating of oxalic acid enables estimates of the age of the
works of art [23]. The presence of the oxalates has been used as indicators of climate
change [24]. The presence of pigments in ancient works of art effected the growth of
lichens on the art works [25]. In calcareous artifacts such as the famous Chinese terra
cotta soldiers or Egyptian epigraphs they lead to a destruction of the surface by form-
ing Ca-oxalate layers and thus to a deterioration of the historian work of art. But in
places where the surface is covered by some blue colours (Egyptian and Chinese
Blue, Chinese Purple) the growth of lichens is inhibited and the artifacts are well pre-
served. The copper ion contained in the pigments is responsible for this effect since
copper is a strong poison for micro-organisms [25]. Weddellite and whewellite very
often occur together with gypsum on the surface of calcareous artifacts exposed in the
Mediterranean urban environment, as main constituents of reddish patinas called in
Italy ‘scialbatura’. The origin of this is a matter of controversy. The observation of
the interface between calcite substratum and the above mentioned secondary miner-
als is an important step in the explanation of alteration process of artifacts of historic
and artistic interest [26]. Studies of the black paint has shown the presence of oxalates
in the paint with serious implications for remediation [27]. The use of infrared and
Raman spectroscopy for the study of oxalates originated with the necessity to study
renal stones [28, 29]. FT Raman spectroscopy has been used to study urolithiasis dis-
ease that has been studied for many years, and the ethiopathogenesis of stone forma-
tion is not well understood [30].
Whilst there have been several studies of synthetic metal oxalates [31–37], few
studies of natural oxalates have been forthcoming and few spectroscopic studies of
the iron(II) natural oxalate has been undertaken. The objective of this work is to un-
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FROST, WEIER: HUMBOLDTINE
279
dertake a comparative study using a combination of Raman and infrared spectroscopy
combined with a thermal stage [56, 57, 58].
Experimental
Mineral
The humboldtine (sample Number M13748 originated from Bohemia, Czech Repub-
lic) was obtained from the Museum Victoria [18]. The sample was phase analyzed us-
ing X-ray diffraction and the compositions checked using EDX measurements.
Thermal analysis
Thermal decomposition of the natural oxalate was carried out in a TA® Instruments
incorporated high-resolution thermogravimetric analyzer (series Q500) in a flowing
nitrogen atmosphere (80 cm3 min–1). Approximately 50 mg of sample was heated in
an open platinum crucible at a rate of 1.0°C min–1 up to 500°C. The TG instrument
was coupled to a Balzers (Pfeiffer) mass spectrometer for gas analysis. Only selected
gases were analyzed.
Raman microprobe spectroscopy
The crystals humboldtine were placed and orientated on the stage of an Olympus BHSM
microscope, equipped with 10× and 50× objectives and part of a Renishaw 1000 Raman
microscope system, which also includes a monochromator, a filter system and a Charge
Coupled Device (CCD). Raman spectra were excited by a HeNe laser (633 nm) at a reso-
lution of 2 cm–1 in the range between 100 and 4000 cm–1. Repeated acquisition using the
highest magnification was accumulated to improve the signal to noise ratio. Spectra were
calibrated using the 520.5 cm–1 line of a silicon wafer. In order to ensure that the correct
spectra are obtained, the incident excitation radiation was scrambled. Previous studies by
the authors provide more details of the experimental technique. Spectra at elevated tem-
peratures were obtained using a Linkam thermal stage (Scientific Instruments Ltd,
Waterfield, Surrey, England).
Infrared emission spectroscopy
Details of infrared emission spectroscopy has been previously published [38–40].
Spectroscopic manipulation such as baseline adjustment, smoothing and normalisa-
tion were performed using the Spectracalc software package Grams (Galactic Indus-
tries Corporation, NH, USA). Band component analysis was undertaken using the
Jandel ‘Peakfit’ software package, which enabled the type of fitting, function to be
selected and allows specific parameters to be fixed or varied accordingly. Band fit-
ting was done using a Gauss–Lorentz cross-product function with the minimum num-
ber of component bands used for the fitting process. The Gauss–Lorentz ratio was
J. Therm. Anal. Cal., 75, 2004

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FROST, WEIER: HUMBOLDTINE
maintained at values greater than 0.7 and fitting was undertaken until reproducible re-
sults were obtained with squared correlations of r2 greater than 0.995.
Results and discussion
Thermal analysis
The HRTG and MS curves for humboldtine are shown in Figs 1 and 2, respectively. The
TG curve for this mineral is complex. Three stages with multiple steps are observed. The
first step is observed with two mass losses at 130 and 141°C. The second is a broad step
centred upon 235°C. The third stage consists of two mass losses at 312 and 332°C. In
harmony with the TG results, mass spectrometry shows the evolved water in two steps at
126 and 132°C. The carbon dioxide is emitted over a broad temperature range commenc-
ing at 200°C. Two MS carbon dioxide emission peaks are observed at 322 and 354°C.
The values obtained are in agreement with previously published data [41–45].
Fig. 1 High resolution thermogravimetric analysis of humboldtine
Fig. 2 Mass spectrometric analysis of evolved gases from the thermal treatment of humboldtine
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281
Table 1 Results of the Raman spectral analysis (relative intensity at center) of thermally treated
humboldtine
50°C
100°C
150°C
200°C
250°C
300°C
350°C
400°C
450°C
3319
0.118
3325
0.125
3333
0.154
1709
0.007
1708
0.006
1708
0.004
1615
0.012
1614
0.010
1613
0.005
1470
0.154
1469
0.159
1468
0.124
1465
0.179
1464
0.182
1464
0.209
1432
0.061
1430
0.061
1429
0.057
1580
0.056
1382
0.351
1326
0.009
1297
0.527
1294
0.378
1302
0.398
1301
0.361
1298
0.417
1254
0.211
1213
0.237
1194
0.129
1205
0.082
1221
0.111
1061
0.068
1057
0.041
1067
0.033
1061
0.025
1061
0.047
983
0.005
980
0.004
914
0.080
913
0.081
912
0.077
856
0.004
857
0.003
856
0.002
811
0.009
652
0.053
653
0.069
690
0.147
672
0.246
662
0.209
656
0.172
597
0.049
593
0.033
600
0.012
599
0.014
584
0.035
583
0.030
581
0.029
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FROST, WEIER: HUMBOLDTINE
Table 1 Continued
50°C
100°C
150°C
200°C
250°C
300°C
350°C
400°C
450°C
520
0.050
520
0.117
520
0.085
480
0.007
479
0.003
488
0.231
420
0.004
397
0.036
393
0.051
400
0.054
399
0.023
397
0.027
362
0.001
326
0.117
304
0.003
307
0.005
288
0.002
285
0.018
291
0.011
285
0.044
281
0.071
289
0.055
287
0.040
286
0.054
254
0.026
244
0.040
242
0.051
240
0.117
234
0.015
233
0.064
233
0.006
230
0.013
219
0.011
217
0.046
216
0.011
221
0.023
220
0.011
220
0.016
204
0.074
203
0.053
203
0.059
179
0.013
184
0.002
The proposed mass loss steps are as follows:
FeC2O4⋅2H2O→FeC2O4⋅H2O+H2O→FeC2O4+H2O
FeC2O4 →FeO+CO+CO2
and
FeC2O4 →FeCO3 +CO
FeCO3→FeO+CO2
Based on the HRTG results it is suggested that the iron(II) oxalate looses water
in the first stage in steps from the dihydrate to the monohydrate and then to the anhy-
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FROST, WEIER: HUMBOLDTINE
283
drous compound. It is proposed that the iron(II) oxalate then decomposes in two
pathways. The first pathway is the conversion of the iron(II) oxalate to iron(II) oxide
and carbon monoxide and carbon dioxide. Berbenni recently studied the reaction of
lithium carbonate with ferric oxalate [44]. Such an oxalate was also incorporated into
a layer double hydroxide and thermal studies undertaken [46]. Thermal studies of the
naturally occurring mineral iron(II) oxalate are less well known. Recently studies
have shown valuable information can be obtained by using a combination of thermal
analysis and spectroscopic techniques [47–50]. In this work we use a combination of
thermogravimetry and hot stage infrared emission and Raman spectroscopy to study
the thermal decomposition of the natural mineral humboldtine.
Raman spectroscopy
The Raman spectra of the hydroxyl stretching region thermally treated humboldtine are
shown in Fig. 3. The results of the Raman spectroscopic analyses are reported in Table 1.
Humboldtine is iron(II) oxalate dihydrate. The spectra clearly show that the intensity of
the OH stretching mode is lost at temperatures below 200°C. The band is at 3318 cm–1 at
25°C and shifts to 3333 cm–1 at 150°C showing a red shift to the band with thermal treat-
ment. The infrared emission spectra shown in Fig. 4 support the Raman data from the
thermal treatment of humboldtine. The IE spectra are noisy at the lower temperatures;
nevertheless two bands may be identified at 3355 and 3147 cm–1. In the TG experiment
two closely overlapping mass loss steps are observed at 131 and 141°C. The MS experi-
ment shows three water vapour evolutions at 126, 132 and 141°C. The results of the
Raman and infrared emission spectroscopic studies are in harmony with the TG and MS
Fig. 3 Raman spectra of the hydroxyl stretching region of thermally treated humboldtine
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FROST, WEIER: HUMBOLDTINE
Fig. 4 Infrared emission spectra of the hydroxyl stretching region of thermally treated humboldtine
results in that all four experiments show that there is no water remaining in the structure
of the thermally treated humboldtine after 150°C. The TG and MS experiments show at
least two mass loss steps. Such steps were not observed in either the Raman or the IES
experiment as the temperature intervals between successive spectra were two large. It
should be recognised that the band at 3318 cm–1 in the Raman spectrum and the band at
3315 cm–1 in the infrared emission spectrum are not attributable to the same vibrational
mode. The former is ascribed to the OH symmetric stretching vibration and the latter to
the OH antisymmetric stretching vibration. Figures 3 and 4 show somewhat conflicting
information. The OH bands exist in the Raman spectrum at 150°C; the intensity is low in
the infrared emission spectrum at the same temperature. This difference is attributed to
the lack of intensity in the infrared emission spectra at low temperatures. It is only at ele-
vated temperatures that sufficient energy enables quality IE spectra to be obtained.
The Raman spectra of the CO stretching region are shown in Fig. 5. Three bands
are distinguished in the CO stretching region at 1470, 1465 and 1432 cm–1. These
bands are attributed to the CO symmetric stretching vibration. Low intensity bands
are observed in the Raman spectra at 1709 and 1615 cm–1. These bands may be attrib-
uted to the CO antisymmetric stretching vibration. The intensity of these Raman
bands approaches zero by 150°C. If the natural iron(II) oxalate was a single pure
chemical then it might be expected that only a single CO stretching mode would be
observed. Thermal treatment can cause the conversion of the humboldtine from the
dihydrate to the monohydrate and then to the anhydrous iron(II) oxalate. The obser-
vation of three CO symmetric stretching vibrations provides credence to the exis-
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FROST, WEIER: HUMBOLDTINE
285
tence of all three phases. Such a concept of the existence of all three phases is sup-
ported by the TG and MS results which show two distinct steps in the dehydration of
the humboldtine.
Fig. 5 Raman spectra of the 1300 to 1800 cm–1 region of thermally treated humboltine
The IE spectra of the 1100 to 2100 cm–1 region of the thermally treated humboldtine
are shown in Fig. 6. The results of the infrared emission analyses are reported in Table 2.
In the IE spectra at 25, 50 and 75°C, intense bands are observed at 1629 cm–1 and no
bands are observed at around 1480 cm–1. The band at 1629 cm–1 is assigned to the CO
antisymmetric stretching vibration. The band at around 1480 cm–1 observed at higher
temperatures is assigned to the ‘forbidden’ symmetric stretching vibration. At the lower
temperatures the Raman and infrared spectra are mutually exclusive. This mutual exclu-
sion is an indication of a centre of symmetry. Such a centre of symmetry would be
achieved if the iron(II) oxalate was planar. Thermal treatment above 100°C results in the
loss of the mutual exclusion and hence it is concluded that the iron(II) oxalate is no longer
planar but is distorted. It is probable that such distortion arises from stacking faults intro-
duced through thermal treatment [10, 11].
The infrared spectra show quite intense bands centered around 1300 cm–1. These
bands may be assigned to B3u OCO stretching mode. The band is observed
at 1315 cm–1 for aqueous potassium oxalate and at 1313 cm–1 for solid potassium oxa-
late. For weddellite and whewellite bands are observed at 1366 and 1309 cm–1. A
band was observed at 1365 cm–1 and assigned to the OCO stretching mode for syn-
thetic copper(II) oxalate dihydrate [51, 52]. Humboldtine shows a similar infrared
pattern with component bands at 1312 and 1357 cm–1. The IE spectra show intense
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FROST, WEIER: HUMBOLDTINE
Fig. 6 Infrared emission spectra of the 1300 to 1800 cm–1 region of thermally treated humboltine
bands at 1315 cm–1 at 75°C which occurs at 1306 cm–1 at 375°C before the intensity is
lost. A second band is observed at 1360 cm–1 and shows an increase in peak position
with thermal treatment. The band is observed at 1367 cm–1 at 375°C. No bands are
observed in these positions in the Raman spectra. It is probable that this latter band is
attributable to the B2 OCO wagging mode. The results of the IE spectra are in har-
mony with the TG and MS results. IE spectra show that no intensity remains in the
characteristic oxalate spectra after 375°C. The TG results show that two mass loss
steps are observed at 312 and 332°C. The MS results prove the evolution of carbon
dioxide at 322 and 354°C in two mass loss steps. One possible mechanism is that at
temperatures above 140°C and below 322°C, the anhydrous iron(II) oxalate is the de-
composition product of humboldtine. At 322°C the iron(II) oxalate changes from the
bidentate to a mono-dentate ligand and at the second step at 354°C, the mono-dentate
oxalate ligand is lost.
The Raman spectra of the C–C stretching region of the thermally treated
humboldtine are shown in Fig. 7. The band is observed at 914 cm–1 at 75°C and shows a
small blue shift with increasing temperature. Only a single C–C stretching vibration is
observed. A second low intensity band is observed at 856 cm–1 for humboldtine. The
band is assigned to the OCO bending mode. A band is not observed in this position for
potassium oxalate. The results of the Raman spectra of the thermal treatment of the
humboldtine appear to be different from that of either the TG/MS data or the IES data.
The loss of the oxalate seems to occur at significantly lower temperatures in the Raman
thermal stage than in the IE stage. The infrared emission spectra of the 650
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FROST, WEIER: HUMBOLDTINE
287
to 1100 cm–1 region are shown in Fig. 8. The first observation that can be made is that
the C–C stretching mode is either not observed or is only weakly observed in the IE
spectra. After thermal treatment of the humboldtine a very low intensity band is ob-
served at around 913 cm–1. It is possible that this is the infrared forbidden C–C stretch-
ing vibration. A low intensity band is observed at 943 cm–1. A strong IE band is ob-
served 819 cm–1. The first band shows a strong red shift and the latter a blue shift with
thermal treatment (Table 2). These bands are assigned to the OCO bending modes
which are strong in the infrared spectrum and of low intensity in the Raman spectra.
Table 2 Results of infrared emission spectral analysis (relative intensity at center) of thermally
treated humboldtine
75°C
100°C
125°C
150°C
175°C
200°C
225°C
250°C
275°C
1965
0.002
1962
0.001
1963
0.002
1962
0.002
1937
0.003
1929
0.005
1920
0.017
1917
0.004
1918
0.008
1915
0.008
1914
0.007
1912
0.008
1911
0.008
1897
0.008
1896
0.004
1705
0.011
1701
0.034
1701
0.031
1701
0.028
1701
0.023
1700
0.020
1700
0.016
1701
0.013
1629
0.567
1620
0.641
1617
0.559
1617
0.569
1616
0.565
1615
0.572
1615
0.572
1614
0.575
1613
0.582
1552
0.150
1480
0.059
1475
0.072
1475
0.069
1475
0.069
1474
0.067
1474
0.060
1474
0.058
1473
0.059
1360
0.056
1362
0.049
1366
0.045
1367
0.045
1367
0.047
1367
0.045
1367
0.048
1367
0.050
1367
0.050
1315
0.124
1315
0.139
1314
0.150
1313
0.156
1312
0.152
1311
0.152
1311
0.160
1310
0.159
1309
0.162
1182
0.002
1186
0.004
1181
0.002
1181
0.002
1180
0.002
1180
0.002
1179
0.002
1177
0.001
1177
0.001
1133
0.002
1134
0.001
1133
0.001
1132
0.001
1131
0.001
1131
0.001
1130
0.001
1131
0.001
944
0.006
948
0.007
948
0.009
948
0.010
946
0.009
945
0.010
944
0.009
944
0.009
942
0.007
913
0.003
911
0.007
911
0.008
910
0.007
910
0.007
909
0.007
909
0.007
909
0.006
819
0.054
813
0.063
809
0.102
809
0.103
809
0.103
809
0.105
809
0.107
809
0.054
809
0.053
717
0.014
716
0.004
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FROST, WEIER: HUMBOLDTINE
Fig. 7 Raman spectra of the 800 to 1200 cm–1 region of thermally treated humboltine
Fig. 8 Infrared emission spectra of the 650 to 1100 cm–1 region of thermally treated humboltine
The Raman spectra of the thermally treated humboldtine in the 200 to 700 cm–1 re-
gion are shown in Fig. 9. The spectra at 50, 100 and 150°C are similar. Above 200°C,
the spectra are different and closely resemble the Raman spectrum of hematite. At
25°C, bands are observed at 582 and 518 cm–1. The bands are observed at 584
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FROST, WEIER: HUMBOLDTINE
289
Fig. 9 Raman spectra of the 200 to 700 cm–1 region of thermally treated humboltine
and 520 cm–1 at 75°C and show a slight blue shift up to 200°C, after which the intensity
is lost. Significant changes are observed in the very low wavenumber region of
humboldtine before and after 200°C. A set of bands are observed at 204, 244, 288
and 304 cm–1. These bands may be assigned to MO stretching and OMO ring bending
modes. At 200°C, bands are observed at 219, 285 and 397 cm–1. These bands corre-
spond to the low wavenumber bands of hematite.
Conclusions
High resolution TG coupled to an evolved gas mass spectrometer shows that dehy-
dration of humboldtine takes place in two stages at around 130 and 141°C. Such
two-step dehydration supports the concept of iron(II) oxalate dihydrate changing to
iron(II) monohydrate and then to the anhydrous iron(II) oxalate. Such a sequence is
supported by the observation of three CO Raman bands. The thermal treatment of
iron(II) oxalate was also studied by infrared emission spectroscopy. At low tempera-
tures the infrared and Raman spectra are mutually exclusive; this supports the con-
cept that the iron(II) oxalate is planar. At temperatures above the dehydration temper-
ature this mutual exclusion is lost with the appearance in the infrared emission
spectra of a band at 1480 cm–1. The IE spectra strongly support the loss of oxalate
over the 275 to 375 temperature range.
If life existed on Mars at some time in the past or even exists in the present time,
low life forms such as fungi and lichens may exist. Such organisms may be found in
very hostile environments [53–55]. Lichens and fungi can control their heavy metal
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FROST, WEIER: HUMBOLDTINE
intake through expulsion as metal salts such as oxalates. The presence of these oxa-
lates can be used as a marker for the pre-existence of life. Thus the study of the com-
mon natural oxalates is of great importance. The minerals on planets such as Mars
may be explored by robotic devices which carry portable Raman spectrometers with
perhaps fibre optics to collect spectral data. The interpretation of the spectra of natu-
ral oxalates is important for these types of studies.
* * *
The financial and infra-structure support of the Queensland University of Technology Inorganic Mate-
rials Research Program is gratefully acknowledged. The Australian Research Council (ARC) is thanked
for funding Mr Dermot Henry of Museum Victoria.
References
1 H. J. Arnott and M. A. Webb, Scanning Electron Microsc., (1983) 1747.
2 J. E. Chisholm, G. C. Jones and O. W. Purvis, Mineralogical Magazine, 51 (1987) 715.
3 A. Fey-Wyssling, Am. J. Bot., 68 (1981) 130.
4 G. M. Gadd, Mineralogical Soc. Ser., 9 (2000) 57.
5 T. Wadsten and R. Moberg, Lichenologist, 17 (1985) 239.
6 E. Manasse, Rend. Accad. Lincei, 19 (1911) 138.
7 F. Mazzi and C. Garavelli, Periodico mineral, 26 (1957) 269.
8 F. Mazzi and C. L. Garavelli, Periodico mineral, 28 (1959) 243.
9 S. Caric, Bull. Soc. Franc. Mineral Crist., 82 (1959) 50.
10 H. Pezerat, J. Dubernat and J. P. Lagier, Comp. Rend. des Siences de l’Acad. des Sci.,
Ser. C: Sciences Chimiques, 288 (1968) 1357.
11 J. Dubernat and H. Pezerat, J. Appl. Cryst., 7 (1974) 387.
12 P. V. Monje and E. J. Baran, Plant Phys., 128 (2002) 707.
13 J. P. Pestaner, F. G. Mullick, F. B. Johnson and J. A. Centeno, Arch. Pathology and Lab. Med.,
120 (1996) 537.
14 J. Dubernat and H. Pezerat, J. Appl. Cryst., 7 (1974) 387.
15 H. Pezereat, J. Dubernat and J. P. Lagier, C. R. Acad. Sci., Paris, Ser. C, 288 (1968) 1357.
16 M. J. Wilson and P. Bayliss, Mineral. Magazine, 51 (1987) 327.
17 R. M. Clarke and I. R. Williams, Mineral. Magazine, 50 (1986) 295.
18 K. Rezek, J. Sevcu, S. Civis and J. Novotny, Casopis pro Mineralogii a Geologii, 33 (1988) 419.
19 H. Winchell and R. J. Benoit, Am. Mineral., 36 (1951) 590.
20 A. Piterans, D. Indriksone, A. Spricis and A. Actins, Proc. Latvian Acad. of Sci., section. B,
Natural, Exact and Applied Sciences, 51 (1997) 254.
21 M. del Monte and C. Sabbioni, Environ. Sci. Technol., 17 (1983) 518.
22 M. del Monte and C. Sabbioni, Sci. Total Environm., 50 (1986) 165.
23 J. Girbal, J. L. Prada, R. Rocabayera and M. Argemi, Radiocarbon, 43 (2001) 637.
24 S. Moore, M. J. Beazley, M. R. McCallum and J. Russ, Preprints of Extended Abstracts presented
at the ACS National Meeting, American Chemical Society, Division of Environm. Chemistry,
40 (2000) 4.
25 I. Lamprecht, A. Reller, R. Riesen and H. G. Wiedemann, J. Therm. Anal. Cal., 49 (1997) 1601.
26 R. Alaimo and G. Montana, Neues Jahrbuch fuer Mineralogie, Abhandlungen, 165 (1993) 143.
J. Therm. Anal. Cal., 75, 2004

FROST, WEIER: HUMBOLDTINE
291
27 G. Alessandrini, L. Toniolo, F. Cariati, G. Daminelli, S. Polesello, A. Pozzi and A. M. Salvi,
Studies in Conservation, 41 (1996) 193.
28 H. Moenke, Chem. Erde, 21 (1961) 239.
29 M. Daudon, M. F. Protat, R. J. Reveillaud and H. Jaeschke-Boyer, Kidney Int., 23 (1983) 842.
30 C. Paluszkiewicz, M. Galka, W. Kwiatek, A. Parczewski and S. Walas, Biospectroscopy,
3 (1997) 403.
31 R. I. Bickley, H. G. M. Edwards and S. J. Rose, J. Molecular Structure, 243 (1991) 341.
32 H. Chang and P. J. Huang, Anal. Chem., 69 (1997) 1485.
33 D. Duval and R. A. Condrate, Sr., Applied Spectroscopy, 42 (1988) 701.
34 H. G. M. Edwards, D. W. Farwell, R. Jenkins and M. R. D. Seaward, J. Raman Spectroscopy,
23 (1992) 185.
35 I. I. Kondilenko, P. A. Korotkov, N. G. Golubeva, V. A. Klimenko and A. I. Pisanskii,
Optika i Spektroskopiya, 45 (1978) 819.
36 O. I. Kondratov, E. A. Nikonenko, I. I. Olikov and L. N. Margolin, Zh. Neorg. Khim.,
30 (1985) 2579.
37 T. A. Shippey, J. Molecular Structure, 63 (1980) 157.
38 R. L. Frost, Z. Ding, J. T. Kloprogge and W. N. Martens, Thermochim. Acta, 390 (2002) 133.
39 R. L. Frost, Z. Ding, W. N. Martens and T. E. Johnson, Thermochim. Acta, 398 (2003) 167.
40 R. L. Frost, J. Kristóf, E. Horváth and J. T. Kloprogge, J. Raman Spectrosc., 32 (2001) 873.
41 J. Praharaj, S. K. Pati, S. C. Moharana and D. Bhatta, J. Teaching and Res. Chem., 8 (2001) 4.
42 A. V. Shkarin, I. P. Suzdalev, B. M. Kadenatsi and G. M. Zhabrova, Khim. Vys. Energ.,
2 (1968) 77.
43 B. S. Randhawa, Thermochim. Acta, 254 (1995) 381.
44 V. Berbenni, A. Marini, G. Bruni and R. Riccardi, Thermochim. Acta, 346 (2000) 115.
45 A. Coetzee, D. J. Eve and M. E. Brown, J. Thermal Anal., 39 (1993) 947.
46 S. Carlino and M. J. Hudson, Solid State Ionics, 110 (1998) 153.
47 E. Horváth, J. Kristóf, R. L. Frost, A. Redey, V. Vágvölgyi and T. Cseh, J. Therm. Anal. Cal.,
71 (2003) 707.
48 J. Kristóf, R. L. Frost, J. T. Kloprogge, E. Horváth and E. Makó, J. Therm. Anal. Cal.,
69 (2002) 77.
49 J. Kristóf, R. L. Frost, W. N. Martens and E. Horváth, Langmuir, 18 (2002) 1244.
50 J. Kristóf, E. Horváth, R. L. Frost and J. T. Kloprogge, J. Therm. Anal. Cal., 63 (2001) 279.
51 H. G. M. Edwards and P. H. Hardman, J. Molecular Structure, 273 (1992) 73.
52 H. G. M. Edwards and I. R. Lewis, Spectrochim. Acta, Part A.: Molecular and Biomolecular
Spectroscopy, 50A (1994) 1891.
53 H. G. M. Edwards, E. M. Newton and J. Russ, J. Molecular Structure, 550–551 (2000) 245.
54 H. G. M. Edwards, N. C. Russell, M. R. D. Seaward and D. Slarke, Spectrochim. Acta,
Part A.: Molecular and Biomolecular Spectroscopy, 51A (1995) 2091.
55 H. G. M. Edwards, N. C. Russell and M. R. D. Seaward, Spectrochim. Acta,
Part A.: Molecular and Biomolecular Spectroscopy, 53A (1997) 99.
56 E. Horváth, J. Kristóf, R. L. Frost, A. Redey, V. Vágvölgyi and T. Cseh, Hydrazine-hydrate in-
tercalated halloysite under controlled-rate thermal analysis conditions. J. Therm. Anal. Cal., 71
(2003) 707.
57 R. L. Frost, Z. Ding and H. D. Ruan, Thermal analysis of goethite. Relevance to Australian in-
digenous art. J. Therm. Anal. Cal., 71 (2003) 783.
58 R. L. Frost, W. Martens, Z. Ding and J. T. Kloprogge, DSC and high-resolution TG of synthe-
sized hydrotalcites of Mg and Zn. J. Therm. Anal. Cal., 71 (2003) 429.
J. Therm. Anal. Cal., 75, 2004