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Infrared Spectroscopic Study of Filled Moonstone

Authors:
  • national gold and diamond testing center of China

Abstract and Figures

The laboratory of the National Gold & Diamond Testing Center (NGDTC) encountered some plagioclase (moonstone) beads with blue adularescence. Fifteen of the 22 moonstones fluoresced moderate to strong bluish white to long-wave UV, with the fluorescence visible in fissures. Electron microprobe analysis of one bead and micro-infrared reflectance spectra of all 22 samples indicated a composition nearly identical to albite. The specimens with strong fluorescence exhibited 3053 and 3038 cm(-1) peaks in their direct transmission infrared spectra, confirming impregnation by a material with benzene structure. This treatment can be detected with a standard gemological microscope by observing characteristics such as relief lines.
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28 NOTES & NEW TECHNIQUES GEMS & GEMOLOGY SPRING 2013
In identifying gemstones from the Chinese market
over the last five years, the National Gold & Dia-
mond Testing Center (NGDTC) found that some
treatments usually applied to top-grade colored
stones such as emerald (Johnson et al., 1999) or
jadeite jade (Fritsch et al., 1992) had also been used
to enhance other materials. Impregnated aquama-
rine, tourmaline, and kyanite have all been encoun-
tered. Li et al. (2008) examined the characteristics
and identifying features of filled aquamarine. Wang
and Yang (2008) reported on a filling technology ap-
plied to carvings, beads, and faceted gems from the
jewelry market of Guangdong Province. They also re-
searched the identification of these filled gemstones.
A few months ago, the NGDTC laboratory re-
ceived from a client six bracelets of plagioclase
(moonstone) beads with blue adularescence. The
bracelets were reportedly from Donghai County in
Jiangsu Province, the trading center for crystal quartz.
They displayed moderate to strong bluish white flu-
orescence in an irregular curvilinear pattern, which
caused suspicion. Observing the beads from different
directions showed that the fluorescence was confined
to the fractures, and the authors deduced the presence
of some foreign material. In addition to determining
the mineral composition of the samples, we collected
infrared spectra to confirm the existence of the filling
material and examine its composition.
MATERIALS AND METHODS
The samples came from a strand of 22 moonstone
beads (table 1) that showed beautiful blue adulares-
cence (figure 1). We examined the samples’ standard
gemological properties using an Abbe refractometer,
an ultraviolet fluorescence lamp, and a microscope.
The chemical composition of sample 1 was first de-
termined by electron microprobe analysis at the Chi-
nese Academy of Geological Sciences (CAGS). The
sample was removed from the strand, and a flat surface
was polished oblique to the lamellae of polysynthetic
twinning. After the electron microprobe analysis we
could still see the strongest adularescence of this sam-
ple and collect its infrared spectra for further tests.
CAGS used a JXA-8230 electron microprobe with an
accelerating voltage of 15 kV, a beam current of 20 nA,
and a beam diameter of 5 µm. Jadeite was used as the
Na standard, and Na was run before the other elements
to avoid undercounting sodium. The standard materi-
als for this test were natural minerals and synthetic ox-
ides, and the detection limit was about 100 ppm.
The 22 samples, including sample 1, were also
tested at NGDTC with a Nicolet Nexus 470 Fourier
transfer infrared spectrometer. To collect the micro-
scopic reflective infrared spectra, we used an MCT/B
detector. A total of 32 sample scans were taken at a
resolution of 8.0 cm–1 and a background gain of 4.0.
The Omnic 6.1a software recommends a scanning
wavenumber range of 4000–650 cm–1, and the infrared
INFRARED SPECTROSCOPIC STUDY OF
FILLED MOONSTONE
Jianjun Li, Xiaofan Weng, Xiaoyan Yu, Xiaowei Liu, Zhenyu Chen, and Guihua Li
NOTES & NEW TECHNIQUES
The laboratory of the National Gold & Diamond
Testing Center (NGDTC) encountered some pla-
gioclase (moonstone) beads with blue adulares-
cence. Fifteen of the 22 moonstones fluoresced
moderate to strong bluish white to long-wave UV,
with the fluorescence visible in fissures. Electron
microprobe analysis of one bead and micro-in-
frared reflectance spectra of all 22 samples indi-
cated a composition nearly identical to albite. The
specimens with strong fluorescence exhibited
3053 and 3038 cm–1 peaks in their direct trans-
mission infrared spectra, confirming impregnation
by a material with benzene structure. This treat-
ment can be detected with a standard gemologi-
cal microscope by observing characteristics such
as relief lines.
See end of article for About the Authors.
GEMS & GEMOLOGY, Vol. 49, No. 1, pp. 28–34,
http://dx.doi.org/10.5741/GEMS.49.1.28.
© 2013 Gemological Institute of America
Jianjun G&G Spring 2013_Layout 1 4/12/13 2:32 PM Page 28
spectrometer extended that range to 7800–400 cm–1.
Given the test requirements of the functional group
(4000–2000 cm1) and the fingerprint region of silicate
minerals in reflective infrared spectroscopy, the scan-
ning wavenumber range was set at 1300–500 cm1.
Thompson and Wadsworth (1957) used infrared
spectroscopy to determine albite and anorthite pro-
portions in plagioclase. Li Jianjun et al. (2007) showed
that the infrared spectra will vary when the samples
are tested in different orientations. Thus the authors
sought to obtain infrared spectra from a consistent
crystal orientation to determine whether the samples
had the same composition. We used a simple orienta-
tion method: With the light source directed from the
viewpoint, we looked for the area where the blue adu-
larescence was the strongest and recorded the micro-
infrared reflective spectra of each sample from the
same orientation. Because the chemical composition
of sample 1 was determined by both EPMA and mi-
croscopic reflective infrared spectroscopy, comparing
the spectra of all other samples to that of sample 1 al-
lowed us to determine whether they had the same
composition.
Direct transmission was then applied to each
whole bead to test the existence of the filling mate-
rial using a DTGS KBr detector. A total of 32 sample
scans were taken at a resolution of 8.0 cm–1, a back-
ground gain of 1.0, and a scanning range of 7000–400
cm–1. With air as the background, we collected the
spectra of infrared rays through each whole bead.
RESULTS AND DISCUSSION
Gemological Properties. The samplesspot refractive
index (RI) was approximately 1.53. The RI of the pol-
ished surface on sample 1 was 1.530–1.535. Because
each sample contained a hole for stringing, specific
gravity was not measured due to the possible compli-
cation caused by the holes. Most samples fluoresced
weak to moderate blue-white to long-wave UV (table
NOTES & NEW TECHNIQUES GEMS & GEMOLOGY SPRING 2013 29
Figure 1. These 22
moonstone beads
(4.01–4.31 ct) show
blue adularescence.
Testing showed that
they were impregnated
by a material with ben-
zene structure. Photo
by Jianjun Li.
In Brief
A strand of 22 moonstone beads with blue adulares-
cence displayed an irregular pattern of bluish white
fluorescence, arousing suspicion of treatment.
A combination of standard gemological testing and
infrared spectral analysis showed that the moonstone
had been impregnated by a material with benzene
structure.
While UV fluorescence can indicate the possibility of
impregnation, infrared spectroscopy provides more
conclusive evidence.
Jianjun G&G Spring 2013_Layout 1 4/18/13 11:22 AM Page 29
1; figure 2 left). Only one sample was inert to long-
wave, while three displayed strong fluorescence.
Under short-wave UV their fluorescence was weaker
or inert (figure 2, right). Because the fluorescence was
visible along the fissures, we deduced that there
might be some foreign material within them. Large
fissures would contain more foreign substance, pro-
ducing stronger fluorescence while the beads with no
fissures were inert under UV fluorescence lamp.
Microscopic observation with brightfield illumi-
nation revealed a fine, closely woven needle-shaped
schistose structure (or inclusions) in all samples (fig-
ure 3), while parallel twin layers were visible from
certain directions (figure 4). There was a clear rela-
tionship between twinning planes and adularescence
intensity: Adularescence was the strongest when the
lighting and viewing directions were approximately
perpendicular to the twinning planes. To keep a con-
stant viewing direction, we collected micro-infrared
reflectance spectra of all samples with the incident
infrared rays perpendicular to the twinning planes.
30 NOTES & NEW TECHNIQUES GEMS & GEMOLOGY SPRING 2013
Figure 2. Most of the moonstones fluoresced moderate to strong blue-white to long-wave UV, with the fluorescence
visible in the fissures (left). Under short-wave UV (right), most of them either fluoresced weak bluish white (seen
in the fissures) or were inert. Photo by Jianjun Li.
TABLE 1. Data for the 22 moonstone samples.
Sample
number
1
2–6
7
8
9
10, 11
12
13
14
15
16
17, 18, 19
20, 21
22
1
(polished
section)
Weight
(ct)
4.21
4.01–4.31
3.75
Diameter
(mm)
8.55
8.41–8.63
8.55 x 6.36
Long-wave UV
reaction
Moderate
Moderate
Weak
Strong
Moderate
Very weak
Moderate
Inert
Moderate
Weak
Strong
Moderate
Very weak
Strong
Moderate
Figure 3. Brightfield illumination revealed fine,
closely woven needle-shaped and schistose inclusions
in this 4.18 ct moonstone. Photomicrograph by Jian-
jun Li; magnified 70×.
Jianjun G&G Spring 2013_Layout 1 4/18/13 11:23 AM Page 30
Observing these samples under the microscope with
overhead illumination, we saw many veins on their
surfaces, which appeared similar to the relief lines on
filled aquamarine described by Li et al. (2009). Nev-
ertheless, it was difficult to find the fractured reflec-
tive surfaces we would expect to accompany such
veins; cracks were visible on the surface but barely
penetrated the moonstone (figure 5). Meanwhile, an
unusual residual flat high-relief area (again, see figure
5) was observed in sample 2, but not in any other
moonstone. Similar high-relief areas are common mi-
croscopic features in filled aquamarine (Li et al., 2008)
and thought to be products of incomplete filling. In
other words, they were holes or gas bubbles.
Electron Microprobe Analysis. Complete electron
microprobe data from six analytical points on sample
1 are listed in table 2. Based on the calculation
method of Brandelik (2009), the three components of
sample 1 are albite (Ab), orthoclase (Or), and
anorthosite (An). The calculated composition of sam-
ple 1 was Ab91.01Or1.92An7.07.
Infrared Spectroscopy Analysis. As figure 6 demon-
strates, the 22 samples had very similar micro-in-
frared reflection spectra when they were collected at
the strongest iridescence area (perpendicular to the
polysynthetic twinning plane). This means the sam-
ples had identical mineral composition.
NOTES & NEW TECHNIQUES GEMS & GEMOLOGY SPRING 2013 31
Figure 4. Fine internal parallel layers (polysynthetic
twins) were observed with brightfield illumination.
The circular feature near the center is a hole for
stringing. Photomicrograph by Jianjun Li; magnified
30×.
Figure 5. Veins were observed on the surface of the
moonstones. Only one sample displayed residual flat,
high-relief areas (holes or gas bubbles, indicated by
the blue arrow). Photomicrograph by Jianjun Li; mag-
nified 40×.
TABLE 2. Electron microprobe data of sample 1, calculated as Ab91.01Or1.92 An7.07.
nd = Not detected
No.
LJJ-1-1
LJJ-1-2
LJJ-1-3
LJJ-1-4
LJJ-1-5
LJJ-1-6
SiO2
66.796
66.572
66.524
66.609
66.772
66.573
TiO2
0.008
nd
0.025
0.005
0.014
nd
Al2O3
20.704
20.771
20.844
20.68
20.752
20.747
Cr2O3
0.008
0.002
0.015
0.023
0.011
0.015
FeO
0.044
0.056
0.066
0.075
0.059
0.036
MnO
0.011
nd
0.002
nd
nd
0.02
CaO
1.513
1.472
1.501
1.46
1.521
1.474
MgO
0.008
nd
nd
nd
nd
0.021
NiO
nd
0.003
nd
nd
0.009
nd
K2O
0.358
0.357
0.344
0.312
0.351
0.317
Na2O
10.559
10.376
10.497
10.567
10.84
10.749
P2O5
nd
0.022
0.003
nd
nd
nd
SO3
nd
nd
nd
nd
nd
nd
Total
100.009
99.631
99.821
99.731
100.329
99.952
Jianjun G&G Spring 2013_Layout 1 4/18/13 11:23 AM Page 31
1200–900 cm–1: This region shows the Si-O
stretching vibration bands in SiO4tetrahedral
polymers (Zhang et al., 1986). The 22 samples gen-
erally shared the same peaks or shoulders: 1187,
1040, and 1007 cm1 peaks; a 1140 cm–1 shoulder;
and a shoulder developing to a peak in the 1076
cm1 region.
800–700 cm–1: This region shows the Si-O bend-
ing vibration bands in SiO4tetrahedral polymers,
as well as the Al-O stretching vibration bands in
polyhedral polymers (Zhang et al., 1986). There
were four peaks in all 22 samples.
Below 700 cm–1: These are the stretching vibra-
tion bands of Al-O (and/or Si-O) and the bending
vibration bands of O-Si-O (and/or O-Al-O), pro-
ducing sharp peaks at 652 and 589 cm–1 and the
shoulders between them (Zhang et al., 1986).
As figure 7 shows, the direct transmission in-
frared spectra of the beads with moderate or strong
fluorescence collected from three orthogonal direc-
tions presented absorption peaks at 3053 and 3038
cm–1, which is due to the cumulative frequency in-
volved in the stretching vibration of C-H in benzene
and the bending vibration of the benzene ring (John-
son et al., 1999a,b). The 4344 cm–1 peak was due to
the combined frequencies of the stretching and bend-
ing vibrations of C-H in CH3and CH2(Zhang et al.,
1999), but the peak at about 4065 cm–1 was associated
with the combined frequencies of the stretching vi-
brations of C-H and C-C bands from organic mate-
rial. Interestingly, an earlier study of filled jadeite jade
found a 4060 cm–1 absorption peak, confirming the
filler material as epoxy or a similar substance (Zhang
et al., 1999). Meanwhile, the infrared spectra of un-
treated moonstones from NGDTC’s database
32 NOTES & NEW TECHNIQUES GEMS & GEMOLOGY SPRING 2013
Figure 6. Micro-infrared reflectance spectra of the
moonstone samples were collected at the area of
strongest adularescence (with incident infrared rays
perpendicular to the polysynthetic twinning plane).
The similar patterns indicate a nearly identical
composition.
WAVENUMBER (cm
-1
)
REFLECTANCE
M
ICRO
-I
NFRARED
R
EFLECTANCE
S
PECTRA
1200
1187
1000 800 600
1140
1076
1040
1007
797
708
652
589
22
21
20
19a
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Figure 7. These direct transmission infrared spectra
are from a filled moonstone with moderate fluores-
cence (sample 12) and untreated moonstones from
NGDTC’s database (a, b, and c). Top: The spectra of
two white moonstones (a and b) and an orange
moonstone (c) do not present peaks at 4344, 4065,
3053, and 3038 cm–1. Bottom: The spectra of the
filled moonstone, collected from three orthogonal di-
rections, do show these four peaks. The 4344 cm–1
peak is from the combined frequency related to the
stretching and bending vibration of C-H in the struc-
ture of CH2, and the 4065 cm–1 peak is due to the
combined frequencies of the C-H and C-C stretching
vibrations. The 3053 and 3038 cm–1 peaks are associ-
ated with the combined frequencies of the C-H
stretching vibration and the bending vibration of the
benzene ring.
-10
4500
0
10
20
30
40
50
60
4000 3500 3000 2500 2000
WAVENUMBER (cm
-1
)
-0.2
3053
4500
D
IRECT
T
RANSMISSION
I
NFRARED
S
PECTRA
TRANSMITTANCE (%)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
4000 3500 3000 2500 2000
4065
4344
12
3038
No.a
No.b
No.c
Jianjun G&G Spring 2013_Layout 1 4/12/13 2:32 PM Page 32
showed no peaks at 4344, 4065, 3053, or 3038 cm–1
(again, see figure 7).
Most of the beads showed absorption peaks at
2969, 2927, and 2869 cm–1, associated with the
stretching vibration of CH2. Three strong absorption
peaks at 2962, 2926, and 2872 cm–1 were frequently
found by Johnson et al. (1999a) in a study of emerald
filled by epoxy. The untreated moonstones did not
present these three peaks (again, see figure 7).
From the above tests, we confirmed that all the
beads were filled by a material with the structure of
benzene.
There was a clear difference in the 2927–2869 cm–1
range between the strongly and weakly fluorescent
samples. The strongly fluorescent moonstone had a
strong absorption band, and the weakly fluorescent
samples showed weak absorption (figure 8). This sug-
gests that samples with stronger fluorescence con-
tain more filling.
CONCLUSION
From standard gemological testing, electron micro-
probe analysis, and infrared spectral analysis of the
fluorescent moonstone samples, we reached several
conclusions. The sample tested by electron micro-
probe had a composition of Ab91.01Or1.92An7.07, or al-
bite. Micro-infrared reflectance spectroscopy showed
that all 22 samples had a nearly identical composi-
tion. Microscopic examination revealed curved veins
without the fractured, reflective surfaces expected to
accompany them. These surface features plus the
patterned fluorescence indicated that the samples
were filled. 3053 and 3038 cm1 peaks in their direct
transmission infrared spectra confirmed that the
beads were impregnated by a material with benzene
structure. In terms of identification, UV fluorescence
could indicate the need for further testing, while the
infrared spectra could provide more conclusive evi-
dence of impregnation.
NOTES & NEW TECHNIQUES GEMS & GEMOLOGY SPRING 2013 33
Figure 8. Direct transmission infrared spectra are
shown for samples with very weak fluorescence
(sample 11) and strong fluorescence (sample 22).
Each sample was examined from three orthogonal
directions. The difference between the strongly fluo-
rescent and weakly fluorescent samples at 3053,
3038, 2969, 2927, and 2869 cm–1 is associated with
CH2. Strong fluorescence is associated with a strong
absorption band, and weak fluorescence with weak
absorption.
WAVENUMBER (cm
-1
)
TRANSMITTANCE
D
IRECT
T
RANSMISSION
I
NFRARED
S
PECTRA
3200 3100 3000 2900 2800 2700 2600
3053
3038 2969
2927
2869
22
11
ABOUT THE AUTHORS
Mr. Li (geoli@vip.sina.com) is the technical supervisor on gemology at the National Gold & Diamond Testing Center (NGDTC) and the
senior engineer at the Shandong Provincial Key Laboratory of Metrology and Measurement, Shandong Institute of Metrology. Ms. Weng
is a graduate student and Dr. Yu is a professor at the School of Gemology, China University of Geosciences. Liu Xiaowei is the director
of NGDTC. Dr. Chen is a senior geochemical engineer at the Institute of Mineral Resources, Chinese Academy of Geological Sciences.
Dr. Li is NGDTC’s chemical engineer.
Jianjun G&G Spring 2013_Layout 1 4/12/13 2:32 PM Page 33
34 NOTES & NEW TECHNIQUES GEMS & GEMOLOGY SPRING 2013
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Article
Full-text available
The authors have encountered hundreds of polymer-filled aquamarines in the Chinese jewelry market. This treatment can be identified with a standard gemological microscope, since it has characteristics such as a flash effect and relief lines. In addition, some of the filled fractures fluoresce chalky white to long-wave UV radiation. FTIR spectroscopy reveals diagnostic features at ∼3100-2850 cm-1 that are related to benzene and ethylic C-H bonds in a polymer.
Article
Thesis (Ph. D.)--University of Utah, 1967. Photocopy. Bibliography: leaves 38-40.
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Criteria for distinguishing emerald filling substances were investigated. Thirty-nine fillers were divided into six substance categories - three "presumed natural" (essential oils [including cedarwood oil], other oils, waxes) and three "artificialresin" (epoxy prepolymers, other prepolymers [including UV-setting adhesives], polymers). Regardless of their composition, fillers with R.I.'s of 1.54 or above show flash effects in emeralds. On the basis of Roman and infrared spectroscopy, the fillers could be separated into five spectral groups, A through E. Most, but not all, commonly used artificial resins have spectra distinct from that of cedarwood oil. However, the detection of one substance in a fissure does not imply that all others are absent.
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Usefulness and limitations of using routine FTIR spectra for identifying gemstones compared with the use of classical FTIR spectra using KBr pellets
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Li J.J., Luo Y.P., Chen Zh., Meng L.J. (2007) Usefulness and limitations of using routine FTIR spectra for identifying gemstones compared with the use of classical FTIR spectra using KBr pellets. Australian Gemmologist, Vol. 23, No. 2, pp. 64-70.
Characteristics and identity of filled aquamarine
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Li J.J., Liu X.W., Chen Y.F. et al. (2008) Characteristics and identity of filled aquamarine. China Gems, Vol. 17, No. 1, pp. 187-189 (in Chinese).
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Li J.J., Liu X.W., Li G.H. (2011) Methods for identifying the polymer-filled peristerite. Journal of Gems and Gemmology, Vol. 13, No. 4, pp. 43-46 (Chinese article with English abstract).