Available via license: CC BY 4.0
Content may be subject to copyright.
Citation: Gong, N.; Wang, C.; Xu, S.
Color Origin of Greyish-Purple
Tremolite Jade from Sanchahe in
Qinghai Province, NW China.
Minerals 2023,13, 1049. https://
doi.org/10.3390/min13081049
Academic Editor: Thomas
N. Kerestedjian
Received: 20 June 2023
Revised: 28 July 2023
Accepted: 5 August 2023
Published: 7 August 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
minerals
Article
Color Origin of Greyish-Purple Tremolite Jade from Sanchahe
in Qinghai Province, NW China
Nina Gong 1, * , Chaowen Wang 2and Shuai Xu 3
1Jewelry Institute, Guangzhou Panyu Polytechnic, Guangzhou 511487, China
2Gemmological Institute, China University of Geosciences, Wuhan 430074, China; c.w.wang@cug.edu.cn
3School of Earth Sciences and Engineering, Sun Yat-sen University, Zhuhai 519080, China;
xushuaiany@hotmail.com
*Correspondence: gong.nina@hotmail.com
Abstract:
Greyish-purple tremolite jade has become well known in the past few years, and the origin
of its color has attracted the attention of gemologists. In this study, FT-IR spectra, EPMA, EPR spectra,
micro-XRF, UV–Vis–NIR spectra, and LA-ICP-MS in situ mapping were analyzed to investigate the
chromophore elements. The study sample was chosen from the Sanchahe mine, Qinghai Province,
NW China, which has the typical characteristics of a gradual color change. The FT-IR and EPMA
results revealed that the mineral composition of the dark and light greyish-purple regions of the
sample are primarily composed of tremolite. UV–Vis–NIR spectra demonstrated that the greyish-
purple color is mainly due to strong absorptions at 560 nm and 700 nm and weak absorption at
745 nm in the visible range. The EPR spectra presented ~3400 G six hyperfine lines resulting from
the hyperfine interactions of the unpaired electron with the Mn
2+
nucleus in the octahedral site. The
UV–Vis–NIR and EPR spectra analyses demonstrated that Mn
2+
is the origin of the purple color.
A comparison of the major elements in the light and dark regions indicated that the chromogenic
elements have strong positive correlations with Mn, Cu, and Fe. LA-ICP-MS mapping used to analyze
the first transition metals indicated possible positive correlations between the greyish-purple color
and the trace chromogenic elements. This suggested that the Mn, Cu, and Fe contents are significantly
high in the dark band region. Combining in situ LA-ICP-MS mapping of trace elements, UV–Vis
spectra, and EPR analysis results, it was suggested that Mn, Cu, and Fe are the major contributors to
the greyish-purple color. This study provides a reference for the specific experimental methods to
determine chromophores and the origin of color in tremolite jades.
Keywords:
greyish-purple tremolite jade; nephrite; spectroscopic methods; trace element; Mn; Fe; Cu
1. Introduction
Tremolite jade (nephrite) is a popular gem material in China which has been used for
jewelry and ritual objects since ancient times [
1
]. Tremolite jade is valuable for its unique
grease luster in China. In addition to its luster, the color is also an important factor for
evaluating the quality and price. The highly reputed Hetian in the Xinjiang province is
the area of origin of tremolite jade deposits and was exploited earlier, while the Qinghai
tremolite jade deposit was mined much later after Hetian. Both the Qinghai tremolite jade
deposit and the Hetian tremolite jade deposit are located in the same metallogenic belt of
the Kunlun Mountains. The tremolite jade mine of Qinghai, also known as Kunlun jade,
is 4000 m above sea level and was discovered around 1992. The Qinghai tremolite jade is
mainly composed of tremolite, generally accounting for more than 95%, and has a mineral
composition similar to Hetian. Tremolite jade has a fiber-interleaved structure, and its
transparency is semi-transparent to opaque. Tremolite jade deposits have been found in
Sanchahe, Nachitai, Tuolahai (Yeniugou), Yangpilin, Muocaogou, Dazaohuo, Xiaozaohuo,
Bajiugou, etc. sections in the East Kunlun orogenic belt since 1992 [
2
–
15
]. Tremolite
Minerals 2023,13, 1049. https://doi.org/10.3390/min13081049 https://www.mdpi.com/journal/minerals
Minerals 2023,13, 1049 2 of 13
jade from the Qinghai mine is characterized by fine texture and high transparency, and
their color is more abundant and diversified. The known tremolite jade types of different
colors are white color jade, yellow color jade, Chinese ink color jade, blue-green color jade,
emerald green color jade, dark green color jade, and greyish-purple color jade. The emerald
green jade and the greyish-purple jade are unique varieties of jade in Qinghai, which are
found to be different from other mines [
5
,
10
,
16
]. The greyish-purple jade is only found in
the Sanchahe mine [
17
]. The distinctive color of greyish-purple tremolite jade is similar to
the misty rain sky and is becoming increasingly popular among consumers. Moreover, the
origin of its color has attracted the research interests of gemologists.
Based on a previous study, it can be proposed that Mn
2+
was the major cause of the
purple tone in greyish-purple tremolite jades. In this study, nephrite was analyzed by
laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using a linear
scanning method from light to dark, which indicated that the Mn content increased with
color deepening [
16
]. However, there has been disagreement on the positive correlation
between Mn and color. The electron paramagnetic resonance (EPR) spectra demonstrated
that the absorption intensities of the characteristic spectra of Mn
2+
were not consistent
with the Mn content determined by micro-XRF and LA-ICP-MS. The ultraviolet–visible
(UV–Vis) spectra indicated that the greyish-purple color faded gradually under oxidizing
conditions and heating at 500–800
◦
C. The color fading was attributed to the oxidation of
Fe
2+
or Mn
4+
. Studies have revealed that the greyish-purple color was caused by Fe
2+→
Ti
4+
intervalence charge transfer based on the UV–Vis spectrum and the electron transition of
the Fe atom [
18
]. However, some studies have suggested that the greyish-purple color was
related to Fe3+ and Mn2+ [12,19].
The conventional instrumentation techniques used to determine the elemental dis-
tributions in minerals include electron probe microanalysis (EPMA), X-ray fluorescence
spectroscopy (micro-XRF)/XRD, and LA-ICP-MS. Each technique has its inherent strengths
and limitations. The limitations are mainly related to the detection limits, analytical vol-
umes, sample preparation, and accessibility. The samples were converted into powdered
form for quantification of the major and trace elements, which cannot accurately indicate
the element concentration distribution. Since the chromogenic elements are present in
trace amounts (i.e., wt% or p.p.m), in situ analysis of elemental concentrations generally
with LA-ICP-MS mapping analysis has emerged as a technique for 2D elemental mapping
with excellent detection limits (p.p.m) over a wide isotopic range (
7
Li to
238
U) in different
minerals [
20
–
23
]. In this technique, the images are stitched together by the post-acquisition
processing to form a quantified image of the trace-element distribution [
24
–
29
]. Thus, color
variation indicating zoning in minerals obtained using in situ microanalytical methods can
yield important results on the color changes with respect to the changes in color-induced
mechanisms. Moreover, it is possible to reveal the composition of greyish-purple tremo-
lite jades in much greater detail, thereby helping in the investigation of the chromogenic
trace elements of greyish-purple tremolite jades and providing an especially effective and
intuitive approach to determining the color origin of the gemstones.
2. Geological Setting
The Sanchahe mine (94
◦
22.125 E, 35
◦
54.627 N) is located 73.4 km north of Golmud City
at an elevation of 4250 m (Figure 1a) [
6
]. It lies north of the fracture belt of the South Kunlun
Mountains and south of the Central Kunlun Suture Zone (CKSZ). The CKSZ separates
the Northern and the Southern Kunlun region and represents the collision between plates
of the northern and southern sides in the late Precambrian and the late Paleozoic and
the closure of the Paleo-Tethyan major oceanic basin [
30
,
31
]. Evidence indicated that
there were episodes of magmatic activity from the Proterozoic to the late Cretaceous with
active tectonic movement and well-developed faults, thereby creating favorable geological
conditions conducive to the formation of tremolite jades.
Minerals 2023,13, 1049 3 of 13
Minerals 2023, 13, x FOR PEER REVIEW 3 of 13
Figure 1. (a) Location of the Sanchahe mine in Qinghai of China (the red triangle marked in the
map); (b) a photo of the sample: the main study area is marked by the red doed lines.
The tectonic contact relationship of tremolite jade can be divided into gradual contact
(hydrothermal metasomatic) and sharp contact (hydrothermal filling and metasomatism).
The hydrothermal metasomatic type tremolite jade orebody occurs in the contact zone
between carbonate rocks and igneous rocks. The metallogenic belt has undergone severe
tectonic movements. The economic value of tremolite jade is always affected by the car-
bonate rocks. On the other hand, the orebody is crumbling towards the igneous rocks. The
major type of tremolite jade in this type is greyish-purple tremolite jade. The hydrother-
mal filling and metasomatism-type tremolite jade orebody are primarily layered or veins
and occur in the fractures in adjacent carbonate rocks. The sharp contact type lode is dis-
tributed along the surrounding carbonate rock strata. It is observed that this type of jade
has weak tectonic reworking, and its quality is poor. Based on the relationship between
the orebody and the surrounding rocks, it can be stated that the tremolite jade deposit is
the contact metasomatic ore, formed when the intermediate basic volcanic rocks intrude
into the carbonate rocks. The tremolite crystallizes and precipitates rapidly after a sudden
drop in the hydrothermal temperature and pressure. Tremolite jade is subjected to re-
peated ore-forming fluid migration and precipitation. The major element Si in tremolite
jade is provide by the intermediate basic volcanic rocks and the elements Mg and Ca that
derive from carbonate rocks.
3. Sampling and Analytical Methods
The sample collected from the Sanchahe mine was greyish-purple tremolite jade (Fig-
ure 1b). The greyish-purple color tremolite is frequently associated with white and green-
white jades, which are transitional to each other. A typical tremolite jade sample in which
the color changes from light to dark was selected to investigate the origin of the greyish-
purple color. This jade was the greyish-purple color tremolite jade with different color
shades showing a clear demarcation between light and dark colors (Figure 1b).
3.1. FT-IR and EPMA
The in situ mineralogical composition of the experimental bulk samples was ana-
lyzed using Fourier transform infrared (FT-IR) spectrophotometer analysis and the EPMA
method. The FT-IR spectra were recorded on a Tensor 27 FT-IR spectrometer (Bruker, Ger-
many). FT-IR analysis was carried out over the range from 400 to 4000 cm
−1
with 4 cm
−1
resolution, with a runtime of 30 s per scan, room temperature of 25 °C, and 50 ± 5% relative
humidity. This analysis was separately carried out for the light-color and dark-color re-
gions, and the tested points are shown in Figure 2.
Figure 1.
(
a
) Location of the Sanchahe mine in Qinghai of China (the red triangle marked in the map);
(b) a photo of the sample: the main study area is marked by the red dotted lines.
The tectonic contact relationship of tremolite jade can be divided into gradual contact
(hydrothermal metasomatic) and sharp contact (hydrothermal filling and metasomatism).
The hydrothermal metasomatic type tremolite jade orebody occurs in the contact zone
between carbonate rocks and igneous rocks. The metallogenic belt has undergone severe
tectonic movements. The economic value of tremolite jade is always affected by the car-
bonate rocks. On the other hand, the orebody is crumbling towards the igneous rocks. The
major type of tremolite jade in this type is greyish-purple tremolite jade. The hydrothermal
filling and metasomatism-type tremolite jade orebody are primarily layered or veins and
occur in the fractures in adjacent carbonate rocks. The sharp contact type lode is distributed
along the surrounding carbonate rock strata. It is observed that this type of jade has
weak tectonic reworking, and its quality is poor. Based on the relationship between the
orebody and the surrounding rocks, it can be stated that the tremolite jade deposit is the
contact metasomatic ore, formed when the intermediate basic volcanic rocks intrude into
the carbonate rocks. The tremolite crystallizes and precipitates rapidly after a sudden drop
in the hydrothermal temperature and pressure. Tremolite jade is subjected to repeated
ore-forming fluid migration and precipitation. The major element Si in tremolite jade is
provide by the intermediate basic volcanic rocks and the elements Mg and Ca that derive
from carbonate rocks.
3. Sampling and Analytical Methods
The sample collected from the Sanchahe mine was greyish-purple tremolite jade
(Figure 1b). The greyish-purple color tremolite is frequently associated with white and
green-white jades, which are transitional to each other. A typical tremolite jade sample
in which the color changes from light to dark was selected to investigate the origin of the
greyish-purple color. This jade was the greyish-purple color tremolite jade with different
color shades showing a clear demarcation between light and dark colors (Figure 1b).
3.1. FT-IR and EPMA
The in situ mineralogical composition of the experimental bulk samples was analyzed
using Fourier transform infrared (FT-IR) spectrophotometer analysis and the EPMA method.
The FT-IR spectra were recorded on a Tensor 27 FT-IR spectrometer (Bruker, Germany).
FT-IR analysis was carried out over the range from 400 to 4000 cm
−1
with 4 cm
−1
resolution,
with a runtime of 30 s per scan, room temperature of 25
◦
C, and 50
±
5% relative humidity.
This analysis was separately carried out for the light-color and dark-color regions, and the
tested points are shown in Figure 2.
Minerals 2023,13, 1049 4 of 13
Minerals 2023, 13, x FOR PEER REVIEW 4 of 13
Figure 2. (a) The FT-IR spectra of the sample. The test points of D1, D2, and D3 lie at the dark band;
L1 and L2 lie at the light-color area right beside the band. (b) A
larger version of the IR finger-
print characteristic absorption of the test points.
To confirm whether the color distribution in the FT-IR results is caused by the impu-
rity minerals or chromogenic elements, EPMA was further performed to investigate the
mineral composition around the color boundary. The major and trace elements were de-
termined using JXA-iSP100 with EPMA (JEOL, Japan). The following conditions were
adopted for analysis of both the major and trace elements of the sample as described in
previous studies: 15 kV acceleration voltage, 2 nA beam current, and 5 µm beam spot size.
Two different analysis conditions were applied in one analytical seing. WDS was set as
one TAP for Mg (Kα), Al (Kα), Na (Kα), and Si (Kα); one LIFH for Ni (Kα), Cu (Kα), and
Mn (Kα); one PETL for K (Kα), P (Kα), and Ca (Kα); one LIF for Fe (Kα); and one LIFL for
Cr (Kα). The natural minerals and synthetic oxides that were used for calibration are di-
opside (Mg, Ca, and Mg), spodumene (Al), orthoclase (K), Cr
2
O
3
(Cr), olivine (Fe), albite
(Na), rhodonite (Mn), apatite (P), Ni2Si (Ni), and Cu (Cu). The ZAF modification proce-
dure was applied for data correction (CITIZAF).
3.2. Micro-XRF and LA-ICP-MS
The in situ major element compositions of the bulk tremolite jade samples were ana-
lyzed by the X-ray fluorescence (micro-XRF) using a Shimadzu micro-XRF-1800 analyzer
(90 mA, 40 kV, and Re anode; Kyoto, Japan). The analysis conditions adopted were a 2 nA
beam current and 5 µm beam spot size.
The in situ trace-element mapping of the bulk tremolite jade samples was performed
using an NWR 193 nm ArF Excimer laser-ablation system coupled to an iCAP RQ ICP-
MS. The ICP-MS was tuned using glass standards NIST 610 and NIST 612 to yield low
oxide production rates. The carrier gas He (0.7 L/min) was fed into the cup, and the aerosol
was subsequently mixed with 0.79 L/min Ar make-up gas. The following 13 isotopes were
selected and measured in all the samples:
24
Mg,
29
Si,
34
S,
43
Ca,
45
Sc,
47
Ti,
51
V,
53
Cr,
55
Mn,
57
Fe,
60
Ni,
65
Cu, and
66
Zn, corresponding to a total dwell time of 105 ms. The laser fluence was
3.5 J/cm
2
, with a repetition rate of 15 Hz and a spot size of 25 µm corresponding to the
scan speed of 110 µm/s. The raw isotope data were reduced using the baseline subtract
and trace elements data reduction scheme (DRS). The DRS is based on the Iolite package
outlined in Paton et al., 2011 [32]. In Iolite, user-defined time intervals are established for
Figure 2. (a) The FT-IR spectra of the sample. The test points of D1, D2, and D3 lie at the dark band;
L1 and L2 lie at the light-color area right beside the band. (
b
) A larger version of the IR fingerprint
characteristic absorption of the test points.
To confirm whether the color distribution in the FT-IR results is caused by the impurity
minerals or chromogenic elements, EPMA was further performed to investigate the mineral
composition around the color boundary. The major and trace elements were determined
using JXA-iSP100 with EPMA (JEOL, Japan). The following conditions were adopted for
analysis of both the major and trace elements of the sample as described in previous studies:
15 kV acceleration voltage, 2 nA beam current, and 5
µ
m beam spot size. Two different
analysis conditions were applied in one analytical setting. WDS was set as one TAP for
Mg (K
α
), Al (K
α
), Na (K
α
), and Si (K
α
); one LIFH for Ni (K
α
), Cu (K
α
), and Mn (K
α
); one
PETL for K (K
α
), P (K
α
), and Ca (K
α
); one LIF for Fe (K
α
); and one LIFL for Cr (K
α
). The
natural minerals and synthetic oxides that were used for calibration are diopside (Mg, Ca,
and Mg), spodumene (Al), orthoclase (K), Cr
2
O
3
(Cr), olivine (Fe), albite (Na), rhodonite
(Mn), apatite (P), Ni
2
Si (Ni), and Cu (Cu). The ZAF modification procedure was applied
for data correction (CITIZAF).
3.2. Micro-XRF and LA-ICP-MS
The in situ major element compositions of the bulk tremolite jade samples were
analyzed by the X-ray fluorescence (micro-XRF) using a Shimadzu micro-XRF-1800 analyzer
(90 mA, 40 kV, and Re anode; Kyoto, Japan). The analysis conditions adopted were a 2 nA
beam current and 5 µm beam spot size.
The in situ trace-element mapping of the bulk tremolite jade samples was performed
using an NWR 193 nm ArF Excimer laser-ablation system coupled to an iCAP RQ ICP-MS.
The ICP-MS was tuned using glass standards NIST 610 and NIST 612 to yield low oxide
production rates. The carrier gas He (0.7 L/min) was fed into the cup, and the aerosol was
subsequently mixed with 0.79 L/min Ar make-up gas. The following 13 isotopes were
selected and measured in all the samples:
24
Mg,
29
Si,
34
S,
43
Ca,
45
Sc,
47
Ti,
51
V,
53
Cr,
55
Mn,
57
Fe,
60
Ni,
65
Cu, and
66
Zn, corresponding to a total dwell time of 105 ms. The laser fluence
was 3.5 J/cm
2
, with a repetition rate of 15 Hz and a spot size of 25
µ
m corresponding to the
scan speed of 110
µ
m/s. The raw isotope data were reduced using the baseline subtract
and trace elements data reduction scheme (DRS). The DRS is based on the Iolite package
outlined in Paton et al., 2011 [
32
]. In Iolite, user-defined time intervals are established for
the baseline correction procedure for calculating the session-wide baseline-corrected values
Minerals 2023,13, 1049 5 of 13
for each isotope. The trace elements were calibrated by considering the glass standards
NIST612 and NIST 610 as external standards.
3.3. UV–Vis–NIR
The UV–Vis–NIR spectroscopy was performed using a UV–Vis spectrophotometer
(UV-3600; Shimadzu, Tokyo, Japan) at the following operating conditions: wavelength
range of 300–800 nm, slit width of 2 nm, high scanning speed, and sampling
interval of 0.2 s
.
3.4. EPR
The paramagnetic centers of greyish-purple tremolite jade powder were investigated
with EPR spectroscopy using a Bruker EMXPlus-10/12 spectrometer (Bruker Corporation,
Billerica, MA, USA) operated with X-band microwave frequencies at both room temperature
and liquid-nitrogen temperature. The experimental conditions for room-temperature EPR
were as follows: a microwave frequency of ~9.83 GHz, a modulation frequency of 100 kHz,
a modulation amplitude of 4 G, and a microwave power of 20 mW. The spectral bands
were obtained over a wide spectral range of 500–5000 mT.
4. Results
4.1. Mineralogical Characteristics
Figure 2a shows the five reflection spectra in FT-IR, three of which were based on the
darker banded region, marked as YQ-1-D1, YQ-1-D2, and YQ-1-D3, and the other two
were from the lighter part, marked as YQ-1-L1 and YQ-1-L2. The five spectra indicate the
reflectance spectral features of tremolite. There were only small differences in the peak
positions of the lighter and the darker parts at the medium- to the low-frequency range.
The FT-IR fingerprint characteristic absorption is shown in Figure 2b. The spec-
tral band between 1200 and 900 cm
−1
is assigned to the asymmetric stretching of the
Si-O-Si and O-Si-O vibrations [
33
–
37
] in tremolite. These several shoulders and peaks near
1153 cm
−1
and 1096 cm
−1
are attributed to the v(Si-O) stretching, 1064 cm
−1
is attributed
to the vas (O-Si-O) stretching, and 1008 cm
−1
and 923 cm
−1
are attributed to the Si-O-Si
stretching. The IR absorption peaks (around 1000 cm
−1
) of the D1, D2, and D3 points at the
dark band shifted a little to lower wave numbers compared to the L1 and L2 points at the
light band, which indicated that elements Fe
2+
and Fe
3+
were increasing [
38
]. The sharp
peaks observed in the lower spectral region (700–400 cm
−1
) are attributed to the symmetric
stretching of the Si-O-Si linkage [
33
,
35
,
37
]. The weak reflection peak around 3660 cm
−1
is attributed to the bending modes of the OH group [
19
,
33
,
35
,
39
] and the Si-O-Si vibra-
tions that may appear [
40
]. The -OH observed in this spectral range is mainly related to
Mg (M1, M3) and the substitute metal element such as Fe. The spectral band at 3970 cm
−1
is attributed to the Mg-OH stretching vibration and the Mg2+ sites in M1 and M2.
A less intense region was observed between 900 cm
−1
and 400 cm
−1.
The spectral
bands at 765 cm
−1
and 642 cm
−1
were attributed to Si-O-Si [
41
,
42
], where the absorbance
peak at 765 cm
−1
is the typical wave number attributable to tremolite [
39
,
43
]. The two
weak bands at 550 cm
−1
and 473 cm
−1
are attributed to the Si-O and M (transition-metal)-O
bending vibrations [44], where M can be Fe, Ti, Mn, Cr, etc.
The EPMA test was used to further confirm the major mineral composition and to
detect the key elements contributing to the greyish-purple color. This detection focused on
the transition region between the lighter greyish-purple to the darker color bands (Figure 3).
The EPMA indicated that the mineral content of the sample consisted of almost homoge-
neous tremolite with few other minerals. The theoretical values implied that the major
components were SiO
2
(59.1–59.4%), CaO (13.1–13.2%), and
MgO (25.1–25.2%) [45–47]
.
Five spots numbered YQ-1-1 to YQ-1-5 indicating color ranging from light to dark were
tested, and the results are shown in Table 1. The first transition-metal ions, including Cr,
Fe, Ni, Mn, and Cu, were detected. Cr and Ni were observed at low levels. The Ti element
reported in the previous study was not detected [
10
]. Fe content was higher than other
Minerals 2023,13, 1049 6 of 13
transition elements detected. Mn content tends to increase with color deepening. The
highest value of Cu was also the value of Mn at the darkest spot of YQ-1-5.
Minerals 2023, 13, x FOR PEER REVIEW 6 of 13
Cr, Fe, Ni, Mn, and Cu, were detected. Cr and Ni were observed at low levels. The Ti
element reported in the previous study was not detected [10]. Fe content was higher than
other transition elements detected. Mn content tends to increase with color deepening.
The highest value of Cu was also the value of Mn at the darkest spot of YQ-1-5.
Figure 3. The EPMA test area of the sample. (a) Partial enlarged photo of the sample: the main study
area is marked by the red doed lines; (b) mineral micrograph of the sample; (c) orthogonal polar-
izing micrograph of the sample; (d) the tested points.
Table 1. Chemical composition of the sample, as determined by EPMA. Oxides (wt%).
Spots
MgO Al
2
O
3
K
2
O CaO Cr
2
O
3
FeO Na
2
O SiO
2
NiO MnO P
2
O
5
CuO Total
YQ-1-1
25.17
0.12
0.03 13.22
0.00
0.11 0.06
59.65
0.00 0.02
0.00
0.01
98.37
YQ-1-2
25.21
0.13
0.05 12.78
0.02
0.06 0.06
59.56
0.02 0.01
0.00
0.01
97.89
YQ-1-3
25.13
0.09
0.04 13.25
0.01
0.08 0.05
59.43
0.04 0.02
0.01
0.01
98.15
YQ-1-4
25.13
0.10
0.04 13.16
0.00
0.13 0.07
59.21
0.01 0.03
0.01
0.01
97.89
YQ-1-5
25.19
0.13
0.03 12.95
0.00
0.09 0.07
59.24
0.00 0.04
0.00
0.03
97.77
Average
25.16
0.11
0.03 13.10
0.00
0.11 0.05
59.34
0.01 0.02
0.00
0.02
97.96
Sigma
0.11 0.02
0.01 0.16 0.01
0.05 0.01
0.19
0.01 0.01
0.00
0.02
0.28
4.2. Elemental Characteristics
4.2.1. Micro-XRF and LA-ICP-MS
Micro-XRF is an efficient, effective, and non-destructive technique for the detection
of the major elements in the samples. Ten test points marked as YQ-1-XD1, YQ-1-XD2,
YQ-1-XD3, YQ-1-XD4, and YQ-1-XD5 (from the dark banded area) and YQ-1-XL1, YQ-1-
XL2, YQ-1-XL3, YQ-1-XL4, and YQ-1-XL5 (from the lighter part) were chosen. The micro-
XRF analysis results of the ten selected points of the sample are shown in Table 2. The data
indicated that the major element components of the tremolite are Si (50.815–52.196 wt%),
Ca (26.486–27.239 wt%), and Mg (20.166–20.845 wt%). For the transition-metal M, the av-
erage values of Fe (0.539 wt%), Mn (0.063 wt%), and Cu (0.0264 wt%) at the dark band are
Figure 3.
The EPMA test area of the sample. (
a
) Partial enlarged photo of the sample: the main
study area is marked by the red dotted lines; (
b
) mineral micrograph of the sample; (
c
) orthogonal
polarizing micrograph of the sample; (d) the tested points.
Table 1. Chemical composition of the sample, as determined by EPMA. Oxides (wt%).
Spots MgO Al2O3K2O CaO Cr2O3FeO Na2O SiO2NiO MnO P2O5CuO Total
YQ-1-1 25.17 0.12 0.03 13.22 0.00 0.11 0.06 59.65 0.00 0.02 0.00 0.01 98.37
YQ-1-2 25.21 0.13 0.05 12.78 0.02 0.06 0.06 59.56 0.02 0.01 0.00 0.01 97.89
YQ-1-3 25.13 0.09 0.04 13.25 0.01 0.08 0.05 59.43 0.04 0.02 0.01 0.01 98.15
YQ-1-4 25.13 0.10 0.04 13.16 0.00 0.13 0.07 59.21 0.01 0.03 0.01 0.01 97.89
YQ-1-5 25.19 0.13 0.03 12.95 0.00 0.09 0.07 59.24 0.00 0.04 0.00 0.03 97.77
Average
25.16 0.11 0.03 13.10 0.00 0.11 0.05 59.34 0.01 0.02 0.00 0.02 97.96
Sigma 0.11 0.02 0.01 0.16 0.01 0.05 0.01 0.19 0.01 0.01 0.00 0.02 0.28
4.2. Elemental Characteristics
4.2.1. Micro-XRF and LA-ICP-MS
Micro-XRF is an efficient, effective, and non-destructive technique for the detection
of the major elements in the samples. Ten test points marked as YQ-1-XD1, YQ-1-XD2,
YQ-1-XD3, YQ-1-XD4, and YQ-1-XD5 (from the dark banded area) and YQ-1-XL1,
YQ-1-XL2, YQ-1-XL3, YQ-1-XL4, and YQ-1-XL5 (from the lighter part) were chosen. The
micro-XRF analysis results of the ten selected points of the sample are shown in Table 2. The
data indicated that the major element components of the tremolite are
Si (50.815–52.196 wt%)
,
Ca (26.486–27.239 wt%), and Mg (20.166–20.845 wt%). For the transition-metal M, the average
values of Fe (0.539 wt%), Mn (0.063 wt%), and
Cu (0.0264 wt%)
at the dark band are higher
than the average values of Fe (0.4408 wt%),
Mn (0.0482 wt%),
and Cu (0.0318 wt%) in the
light area. However, as mentioned before, Ti was not detected in this test.
Minerals 2023,13, 1049 7 of 13
Table 2. The micro-XRF analysis results of the ten selected points of the sample (wt%).
Sample Si Ca Mg Fe Zn K S Mn Cu Cr V Sr Ce Total
YQ-1-XL1 51.32 26.95 20.85 0.26 0.24 0.07 0.06 0.04 0.02 0.00 0.00 0.01 0.19 100
YQ-1-XL2 51.31 26.96 20.77 0.28 0.24 0.07 0.05 0.04 0.03 0.05 0.00 0.01 0.20 100
YQ-1-XL3 51.34 27.09 20.65 0.31 0.22 0.08 0.02 0.06 0.03 0.02 0.00 0.01 0.18 100
YQ-1-XL4 51.32 27.14 20.70 0.31 0.22 0.07 0.06 0.05 0.03 0.02 0.07 0.01 0.00 100
YQ-1-XL5 50.82 27.23 20.71 1.03 0.01 0.07 0.04 0.05 0.02 0.03 0.00 0.00 0.00 100
YQ-1-XD1 51.18 27.11 20.66 0.86 0.00 0.05 0.03 0.05 0.03 0.03 0.00 0.00 0.00 100
YQ-1-XD2 50.99 27.24 20.78 0.82 0.00 0.06 0.03 0.06 0.03 0.00 0.00 0.00 0.00 100
YQ-1-XD3 51.81 27.09 20.17 0.37 0.20 0.04 0.05 0.06 0.03 0.04 0.00 0.00 0.15 100
YQ-1-XD4 52.20 26.47 20.42 0.32 0.21 0.05 0.03 0.07 0.04 0.00 0.00 0.00 0.20 100
YQ-1-XD5 52.28 26.60 20.17 0.31 0.21 0.04 0.07 0.08 0.04 0.00 0.00 0.00 0.20 100
To further determine the relationship between the greyish-purple color and the
transition-metal M, this study subsequently performed an in situ element LA-ICP-MS
mapping analysis of the trace transition metals. The test region in the element map was
chosen around the small part of the dark band for detecting the relative elemental changes
in the dark band (Figure 4k). These data indicated that the different color regions display
similar Si (Figure 4a), Mg (Figure 4b), and Ca (Figure 4c) contents, but the dark band
presents higher Mn (Figure 4g) and Cu (Figure 4j) and lower Fe (Figure 4h).
Figure 4.
In situ element LA-ICP-MS mapping of the sample. (
a
–
c
) major element Si, Mg, and Ca;
(d–j) first transition-metal elements Ti, V, Cr, Mn, Fe, Ni, and Cu; (k) test region of the sample.
4.2.2. EPR
The EPR experimental spectra are shown in Figure 5. The results of the EPR further
investigated the site occupancy of the first transition metals. The EPR spectrum presents
six hyperfine lines at a magnetic field strength of ~3400 G, and a weak peak at ~1500 G
(Figure 5a). The ~3400 G magnetic hyperfine splitting recorded (Figure 5b) was character-
ized by a broad signal centered at g = 2.015, accompanied by forbidden (MS = 2) transitions
at g = 4 (I = 5/2). The signal at g = ~4.33 (~1550 G) is attributed to Fe3+ (Figure 5a).
Minerals 2023,13, 1049 8 of 13
Minerals 2023, 13, x FOR PEER REVIEW 8 of 13
characterized by a broad signal centered at g = 2.015, accompanied by forbidden (MS = 2)
transitions at g = 4 (I = 5/2). The signal at g = ~4.33 (~1550 G) is attributed to Fe
3+
(Figure 5a).
The EPR spectra reveal three Mn
2+
centers and a rhombic Fe
3+
center at the octahedral
sites (M1, M2, and M3), but the spectrum intensities of Mn
2+
and Fe
3+
are not directly cor-
related with the concentrations of these elements. The main reason being that Mn also
occurs in higher valence states, leading to minor amounts of Fe
3+
substituting for Si
4+
at
the tetrahedral sites (T1 and T2) [18].
Figure 5. Powder EPR spectra of the sample. (a) Six hyperfine lines at a magnetic field strength of ~3400
G, and a weak peak at ~1500 G; (b) partial magnification of six hyperfine lines at ~3400 G in (a).
4.3. UV–Vis–NIR Spectrum Characteristics
The UV–Vis–NIR profiles of greyish-purple color tremolite jade at room air temper-
atures are shown in Figure 6. The absorption spectrum of the sample demonstrated broad
and intense absorption bands at 238 nm, 568 nm, and 960 nm; and five broad and weak
absorption bands at 600 nm, 700 nm, 745 nm, 760 nm, and 890 nm. It also demonstrated
three absorption valley bands at 380 nm, 650 nm, and 940 nm.
Figure 6. The UV–Vis–NIR Spectrum of the sample.
The test points of D1, D2, and D3 lie at the
dark band; L1 and L2 lie at the light-color area right beside the band.
Figure 5.
Powder EPR spectra of the sample. (
a
) Six hyperfine lines at a magnetic field strength
of ~3400 G, and a weak peak at ~1500 G; (
b
) partial magnification of six hyperfine lines at ~3400 G in (
a
).
The EPR spectra reveal three Mn
2+
centers and a rhombic Fe
3+
center at the octahedral
sites (M1, M2, and M3), but the spectrum intensities of Mn
2+
and Fe
3+
are not directly
correlated with the concentrations of these elements. The main reason being that Mn also
occurs in higher valence states, leading to minor amounts of Fe
3+
substituting for Si
4+
at
the tetrahedral sites (T1 and T2) [18].
4.3. UV–Vis–NIR Spectrum Characteristics
The UV–Vis–NIR profiles of greyish-purple color tremolite jade at room air tempera-
tures are shown in Figure 6. The absorption spectrum of the sample demonstrated broad
and intense absorption bands at 238 nm, 568 nm, and 960 nm; and five broad and weak
absorption bands at 600 nm, 700 nm, 745 nm, 760 nm, and 890 nm. It also demonstrated
three absorption valley bands at 380 nm, 650 nm, and 940 nm.
Minerals 2023, 13, x FOR PEER REVIEW 8 of 13
characterized by a broad signal centered at g = 2.015, accompanied by forbidden (MS = 2)
transitions at g = 4 (I = 5/2). The signal at g = ~4.33 (~1550 G) is attributed to Fe
3+
(Figure 5a).
The EPR spectra reveal three Mn
2+
centers and a rhombic Fe
3+
center at the octahedral
sites (M1, M2, and M3), but the spectrum intensities of Mn
2+
and Fe
3+
are not directly cor-
related with the concentrations of these elements. The main reason being that Mn also
occurs in higher valence states, leading to minor amounts of Fe
3+
substituting for Si
4+
at
the tetrahedral sites (T1 and T2) [18].
Figure 5. Powder EPR spectra of the sample. (a) Six hyperfine lines at a magnetic field strength of ~3400
G, and a weak peak at ~1500 G; (b) partial magnification of six hyperfine lines at ~3400 G in (a).
4.3. UV–Vis–NIR Spectrum Characteristics
The UV–Vis–NIR profiles of greyish-purple color tremolite jade at room air temper-
atures are shown in Figure 6. The absorption spectrum of the sample demonstrated broad
and intense absorption bands at 238 nm, 568 nm, and 960 nm; and five broad and weak
absorption bands at 600 nm, 700 nm, 745 nm, 760 nm, and 890 nm. It also demonstrated
three absorption valley bands at 380 nm, 650 nm, and 940 nm.
Figure 6. The UV–Vis–NIR Spectrum of the sample.
The test points of D1, D2, and D3 lie at the
dark band; L1 and L2 lie at the light-color area right beside the band.
Figure 6.
The UV–Vis–NIR Spectrum of the sample. The test points of D1, D2, and D3 lie at the dark
band; L1 and L2 lie at the light-color area right beside the band.
Minerals 2023,13, 1049 9 of 13
5. Discussion
The FT-IR and EPMA analysis indicated that the sample is nearly pure tremolite aggre-
gate and ruled out the possibility of color contributed by the impurity mineral. The official
formula from the IMA Master List for tremolite is Ca
2
(Mg
5.0-4.5
Fe
2+0.0-0.5
)Si
8
O
22
(OH)
2
,
for actinolite it is Ca
2
(Mg
4.5-2.5
Fe
2+0.5-2.5
)Si
8
O
22
(OH)
2,
, and for ferroactinolite it is Ca
2
(Mg
2.5-0.0
Fe
2+2.5-5.0
)Si
8
O
22
(OH)
2
. It is an end member of the tremolite-ferroactinolite se-
ries. The term used is tremolite when the ratio Mg/(Mg + Fe
2+
)
≥
0.90, actinolite when
the ratio Mg/(Mg + Fe
2+
) is between 0.50 and 0.90, and ferroactinolite when the ratio
Mg/(Mg + Fe
2+
) < 0.50 [
39
,
48
,
49
]. The FT-IR results indicated that the weak reflection peak
at around 3670 cm
−1
is due to the bending modes of the OH group [
33
]. The -OH in this
spectral range is mainly related to Mg (M1, M3) and the substitute metals such as Fe. The
spectral band at 3970 cm
−1
is attributed to the Mg-OH stretching vibration and the Mg
2+
in M1 and M2 sites. In addition to the major chemical constituents of Si
4+
, Mg
2+
, and Ca
2+
,
the samples included impurities such as Fe, Mn, Ti, Cu, and Ni. These impurity ions are
generally first transition metals which include the incomplete d orbital. According to the
ligand field theory [
44
], the color of the minerals is due to the absorption radiation of their
electron transitions in the visible range. Each wavelength or frequency of visible light
corresponds to a color. Hence, there can be minerals that selectively absorb visible light at
certain wavelengths or frequencies to produce color. The color of any mineral is the color
of the remaining visible light wavelengths or frequencies not absorbed by that mineral.
When the tremolite containing transition metals is irradiated with light, the electrons in
the d orbital of the transition element in the mineral absorb the energy of the irradiated
light and move from a state of lower energy to a state of higher energy, thereby resulting in
absorption phenomenon and color.
Different electron transitions of the minerals in the visible range lead to the color of the
minerals. The major factors contributing to the color of greyish-purple tremolite jade are as
follows: (1) d–d electronic transition between d electron orbitals, and f–f electron transitions
between lanthanide electron orbitals; (2) electron transition caused by the electric charge
transfer between the adjacent ions (e.g., Fe2+–Fe3+ charge transfer).
The broad absorption between maxima ~500 nm and ~560 nm in the visible range and
maxima at 700 nm and 520 nm in the visible absorption spectrum can lead to a transmission
window at ~400–430 nm that produces the violet color, and this is mainly due to Mn
ion d–d electronic transition. Schmetzer and Bank (1980) pointed out that the absorption
at ~560 nm is attributed to the Fe
2+
–Ti
4+
charge transfer [
36
]. However, the chemical
tests followed in this study could not detect Ti. Thus, the UV–Vis–NIR results of the
investigated sample exhibited a broad absorption band at 560 nm (17,850 cm
−1
), which
is because of Mn
2+
in octahedral coordination for absorption by the d–d transitions of
6
A
1
g(S)
→4
T
1
g(G) [
50
]. The 720–760 nm region is due to the Fe
2+
–Fe
3+
charge transfer in
the tremolite [
51
], and the visible absorption spectrum of Fe
3+
between maxima 430 nm
and 463 nm is caused by the d–d transitions of
6
A
1→
A
1
(
4
G) +
4
E(
4
D). If both the d–d
transitions of Fe
3+
and the Fe
2+
–Fe
3+
charge transfer coexist in the lattice of the tremolite,
the color of the tremolite primarily depends on the latter because of the higher strength of
the electric charge. The absorption bands at ~720 and ~760 nm in the visible absorption
spectrum can lead to a yellowish-green to brownish-green color. In this study, the UV
spectrum of the collected sample demonstrated a very weak narrowband absorption
at 745 nm, and the range between 430 nm to 463 nm is not clearly visible. Therefore,
the absorption of the Fe ion in greyish-purple tremolite jade is primarily because of the
Fe
2+
–Fe
3+
charge transfer. In addition, the optical-absorption maxima in the 690–940 nm
region can be assigned to the d–d electronic transition absorption bands of Cu
2+
[
52
]
and produce a blue to blueish-green color [
53
]. The strong band at ~700 nm is assigned
to the
2
Ag
→2
Bg transitions of Cu
2+
, and the weak band at ~900 nm is assigned to
2
B
1
g
→2
A
1
g. These absorption bands are typically observed in several copper complexes.
The UV–Vis–NIR spectrum of the sample exhibited an absorption band at ~700 nm, which
is much stronger than that at 745 nm, implying that the d–d electronic transition absorption
Minerals 2023,13, 1049 10 of 13
of Cu
2+
plays an important role than the Fe
2+
–Fe
3+
charge transfer. This finding is in
agreement with the EPR analysis result.
The optical-absorption experimental techniques and crystal field theory have been
widely used in the research of the valence states of the transition-metal ions and the ligand
symmetry to illustrate the color of the minerals [
54
–
57
]. A silicon-oxygen tetrahedron
(SiO
4
)
4−
consists of Si surrounded by four oxygen atoms in the shape of a tetrahedron to
form an amphibole crystal structure. The essential characteristic of the amphibole structure
is a double chain of corner-linked Si-O tetrahedrons that extend parallel to the c-axis. The
silica chains are linked by Ca
2+
and Mg
2+
. Five different voids are present between the
silica double chain, namely, M1, M2, M3, M4, and A, where A > M4 > M3
≈
M1 > M2 [
58
].
The occupancy of the Ca
2+
and Mg
2+
cation sites was determined as M1, M2, and M3,
where M1 and M2 are smaller, M3 is slightly larger, and the cations of Ca
2+
and Mg
2+
exist in sixfold coordination. The M1 and M3 coordination octahedrons are composed of
4O
2+
(OH), and the M2 coordination octahedrons are composed of 6O. These coordination
octahedrons are co-angled with each other, forming a band parallel to the c-axis. The
ions with large ionic radius, i.e., Ca
2+
or Na
+
, occupy M4, an 8-fold coordination site.
If the void is occupied by Mn
2+
, Fe
2+
, Cu
2+
, Mg
2+
, etc., it is a sixfold coordination site
leading to octahedral distortion. The ions K
+
and Na
+
with larger radii usually occupy
the cation vacancy sites. The different colors of the tremolite are mainly attributed to the
trace transition elements. Consistent with the data previously recorded by EPMA, the first
transition-metal ions of the greyish-purple color tremolite primarily include Fe, Mn, Ti, Cu,
Ni, etc., all belonging to the first main transition series having an unfilled d orbital. The
EPR spectra indicated that ~3400 G six hyperfine lines are contributed by the hyperfine
interactions between the unpaired electron of transition-metal ion Mn
2+
with the
55
Mn
nucleus in the octahedral site, corresponding to 5/2, 3/2, 1/2, +1/2, +3/2, and +5/2 lines
from low to high magnetic field. The radii of Mn
2+
(0.091 nm) and Mg
2+
(0.078 nm) are
close to each other, and the isomorphous replacement tends to occur between them [
51
].
The resonance absorption spectrum of Mn
2+
is nearly isotropic, indicating that Mn
2+
has
high structural flexibility. In addition, Mg
2+
lies in the center of the octahedral site M2,
and the symmetry of M2 is higher than those of M1 and M3, as previously mentioned.
Thus, Mn
2+
is most likely to substitute Mg
2+
in the M2 site. Similarly, the radius of
Cu
2+
(0.073 nm) is closer to that of Mg
2+
. Therefore, it is also an ideal ion to substitute Mg
2+
in the crystal lattice to form octahedral coordination. The EPR spectrum of Cu
2+
exhibit
typical axial symmetry of ~3100 G, and its g value is ~2.0–2.3 in 298 k [
59
], with the g value
and the peak position approaching those of Mn
2+
. The EPR result of the sample does not
show the Cu
2+
spectra because the Cu
2+
signal curve was overlapped by the Mn
2+
signal
curve or the Cu
2+
signal was beyond the lower instrument detection limit. The EPR can only
detect the Fe
3+
absorption spectrum at room temperature, and the spin-lattice relaxation
time of Fe
2+
is too short to be detected. The spectral lines under the influence of a magnetic
field ~1550 G are close to each other and caused by Fe
3+
quadruple resonance absorption
according to a previous study [
60
]. The intensity of the resonance absorption of Mn
2+
is
stronger than that of Fe
2+
, implying that Mn
2+
is the dominant paramagnetic ion in the
study samples. Yu et al. (2019) analyzed the EPR spectrum of greyish-purple tremolite jade
at the cryogenic temperature of 93 K in their previous study, and the results suggested that
the EPR spectrum between 3440 G and 3460 G is caused by the Ti
4+
resonance absorption at
93 K [
11
]. Luo et al. (2017) also analyzed the cryogenic EPR spectrum of the greyish-purple
color tremolite jade at 77 K and fitted the EPR experiment data at ~3400 G. The fitting line
further confirmed that the resonance signal is mainly due to the spin-forbidden transition
of Mn
2+
[
16
]. The chemical composition results indicated that Ti is very low or not detected
in this study. Therefore, there is no correlational evidence to support the point of view
that the Fe
3+
-Ti
4+
charge transfer is the major reason for the origin of the greyish-purple
color. The major elemental analysis results indicated the Fe, Mn, and Cu elements can
be the chromophore elements. It is suggested that the average values of the Fe, Mn, and
Cu contents in the dark band are higher than those in the light area. This indicated that
Minerals 2023,13, 1049 11 of 13
Cu
2+
is closely related to the greyish-purple color apart from Mn and Fe ions mentioned in
the previous work.
The in situ LA-ICP-MS mapping further confirmed the relationship between Fe, Mn,
Cu, and the greyish-purple color. A 7160
×
5975
µ
m
2
rectangular area was selected on
the lighter greyish-purple to the darker color transition region as the analysis area for
LA-ICP-MS mapping. The first transition-metal data within this area was collected to
investigate the relationships between color variations and the concentration of the first
transition metals. The LA-ICP-MS mapping results demonstrated that the relative concen-
tration distribution of Cu, Mn, and Fe has a positive correlation with the greyish-purple
color, and the degree of element substitution in the dark band region is larger than that
in the light one. The homogeneous distribution patterns of Cr, V, Ni, and Ti illustrate
that these first transition elements have no relationship with the color changes. The most
significant variance is observed in the relative Mn content in the dark band region followed
by Cu and Fe. This further confirmed the contribution of Cu
2+
to the greyish-purple color.
Luo et al. (2017) evaluated the L*a*b* value of the greyish-purple color tremolite slice
of 1 mm thickness, and the calculated dark color was found to be 65, 4, 4 [
16
], with the
corresponding sRGB value of 225, 215, 210. LA-ICP-MS mapping results combined with the
UV–Vis–NIR spectrum analysis indicated that the major visible absorption spectrum band is
the result of the d–d transitions of Mn
2+
, and the d–d transition bands of Cu
2+
are stronger
than the Fe
2+
–Fe
3+
charge transfer. The optical spectroscopy analysis results and the
LA-ICP-MS mapping results were in good agreement with each other. Thus, it can be stated
that Cu
2+
, which was not mentioned in the previous studies, also significantly contributed
to the greyish-purple color.
6. Conclusions
This study mainly combined mineralogical and spectroscopic methods to investigate
greyish-purple color of nephrite from Sanchahe in Qinghai Province, NW China. Both the
UV–Vis–NIR spectrum and the EPR confirmed that the d–d transitions of Mn
2+
primarily
contribute to the greyish-purple color of the tremolite. The limitation of the lower detection
limit can be overcome by the application of the micro-XRF and EPMA tests, which may
indicate the contribution of Cu to the greyish-purple color. The LA-ICP-MS mapping
analysis clearly illustrated the distribution of chromogenic elements and further confirmed
that Mn, Cu, and Fe are positively related to the greyish-purple color. Further, the crystal
field theory analysis also indicated that the d–d transitions of Mn
2+
and Cu
2+
and the
Fe
2+
–Fe
3+
charge transfer are closely related to the greyish-purple color of the tremolite. It
is of utmost significance to study the ionic lattice site occupation of Mn, Cu, and Fe elements
in detail in the future. Moreover, the LA-ICP-MS mapping can be especially useful and
more relevant for understanding the relationships of very low-level color-inducingelements
with the color-inducing mechanism.
Author Contributions:
Conceptualization, N.G.; methodology, N.G.; software, N.G. and S.X.; valida-
tion, N.G., C.W. and S.X.; formal analysis, N.G.; investigation, N.G. and S.X.; resources, N.G.; data
curation, N.G.; writing—original draft preparation, N.G.; writing—review and editing, S.X., N.G.
and C.W.; visualization, N.G. and S.X.; supervision, C.W.; funding acquisition, N.G. All authors have
read and agreed to the published version of the manuscript.
Funding:
This research was funded by the 2022 Tertiary Education Scientific Research Project of
Guangzhou Municipal Education Bureau, grant number 202235328. This research was also funded by
Guangzhou Panyu Polytechnic, grant numbers 220224086 and 210224251.
Data Availability Statement: Not applicable.
Acknowledgments:
The authors are very thankful to Kun Li for providing samples and funds. The
authors are grateful to Yuefeng Zhang, Fangfang Huang, Chengqiang Pan, and Ziwei Tang for the
help and valuable suggestions.
Conflicts of Interest: The authors declare no conflict of interest.
Minerals 2023,13, 1049 12 of 13
References
1.
Qiu, Z.; Zhang, Y.; Li, L.; Li, X.; Qin, S. Discussion on Two Metallogenic Mechanisms of Hetian Jade in Hetian Area, Xinjiang.
J. Jilin Univ. Earth Sci. Ed. 2015,45, 1–2.
2.
Dong, B. Geological Situation and Jade Characteristics of Golmud Jade in Qinghai Province. Nonmet. Geol.
1996
,5, 23–28.
(In Chinese)
3.
Chai, F.; Parati, A. Comparative Study of the Gemological Characteristics of Nephrite of Hetian Jade and Qinghai Jade.
J. Xinjiang Inst. Technol. 2000,1, 77–80.
4. Feng, X.; Zhang, B. Composition and Structural Characteristics of Nephrite from Qinghai. J. Gems Gemmol. 2004,4, 7–9.
5.
Liu, H.; Yang, M.; Yang, T.; Li, J. Study on Colour and Gemmological Characteristics of Viridis Nephrite from Qinghai Province.
J. Gems Gemmol. 2013,15, 7–14.
6.
Zhou, Z.; Liao, Z.; Ma, T.; Yuan, Y. Study on Ore-Forming Type and Genetic Mechanism of Sanchakou Nephrite Depositin Qinghai
Province. J. Tongji Univ. Nat. Sci. 2005,9, 1191–1194.
7.
Wang, J.; Gan, Y.; Li, J.; Wei, J. Analysis on Nephrite Conditions and Discovery Prospects in Dazaohuo Area in Qinghai Province.
Plateau Earthq. Res. 2007,19, 47–51.
8.
Zhou, Z.; Liao, Z.; Chen, Y.; Li, Y.; Ma, T. Petrological and Mineralogical Characteristics of Qinghai Nephrite. Rock Miner. Anal.
2008,1, 17–20.
9.
Yu, H.; Ruan, Q.; Sun, Y.; Li, D. Micro-Morphology and Mineral Composition of Different Color Qinghai Nephrites. Rock Miner. Anal.
2018,37, 626–636.
10.
Yu, H.; Ruan, Q.; Liao, B.; Li, D. Geochemical Characteristics and Ar-Ar Dating of Different Deposits in Qinghai Province.
Acta Petrol. Miner. 2018,37, 655–668.
11.
Yu, H.; Ruan, Q.; Sha, X.; Yang, Y. Study on Color—Causing Elements in Qinghai Nephrite by Elemental Analysis and Electron
Paramagnetic Resonance Spectroscopy. Rock Miner. Anal. 2019,38, 288–296.
12.
Song, H.; Tan, H.; Zu, E. Spectral Characteristics of Qinghai Nephrite with Different Colors. Bull. Chin. Ceram. Soc.
2020
,
39, 242–246.
13.
Hao, N.; Tao, L.; Wang, N.; Zhang, K. Analysis of Spectral Characteristics and Color Causes of Tremolite Jade Inyeniugou,
Qinghai Province. J. Hebei Geo Univ. 2021,44, 11–15.
14.
Zhang, C.; Yu, X.; Yang, F.; Santosh, M.; Huo, D. Petrology and Geochronology of the Yushigou Nephrite Jade from the North
Qilian Orogen, Nw China: Implications for Subduction-Related Processes. Lithos 2021,380–381, 105894. [CrossRef]
15.
Li, Y.; Lai, Y. Study on Metallogenic Mechanism of the Tremolite Jade Deposit in Jiubagou, Qinghai Province. Beijing Da Xue Xue Bao
2021,57, 1087–1100.
16.
Luo, Z.; Shen, A.; Yang, M. Study on Color Quantitative Expression, Replication and Color Origin of Gray-Purple Nephrite from
Qinghai, China Based on Spectroscopy Methods. Spectrosc. Spectr. Anal. 2017,37, 822–828.
17. Zhang, B. Systematic Gemology; Geology Press: Beijing, China, 2006. (In Chinese)
18.
Yu, H. Coloring and Metallogenic Mechanisms of Different Colors in Qinghai Nephrite. Ph.D. Thesis, Nanjing University,
Nanjing, China, 2016.
19.
Hao, N.A. Gemological Study of Tremolite Jade in Yeniugou, Qinghai. Master’s Thesis, Hebei GEO University, Shijiazhuang,
China, 2021.
20.
Jackson, S.E.; Longerich, H.P.; Dunning, G.R.; Freyer, B.J. The Application of Laser-Ablation Microprobe; Inductively Coupled
Plasma-Mass Spectrometry (Lam-Icp-Ms) to in Situ Trace-Element Determinations in Minerals. Can. Miner. 1992,30, 1049–1064.
21.
Norman, M.D.; Pearson, N.J.; Sharma, A.; Griffin, W.L. Quantitative Analysis of Trace Elements in Geological Materials by
Laser Ablation Icp-Ms: Instrumental Operating Conditions and Calibration Values of Nist Glasses. Geostand. Geoanal. Res.
1996
,
20, 247–261. [CrossRef]
22.
Günther, D.; Frischknecht, R.; Heinrich, C.A.; Kahlert, H.J. Capabilities of an Argon Fluoride 193 Nm Excimer Laser for Laser
Ablation Inductively Coupled Plasma Mass Spectometry Microanalysis of Geological Materials. J. Anal. At. Spectrom.
1997
,
12, 939–944. [CrossRef]
23.
Hinchey, J.G.; Wilton, D.H.C.; Tubrett, M.N.; Jackson, S.E.; Guenther, D.; Sylvester, P.J. A Lam-Icp-Ms Study of the Distribution of
Gold in Arsenopyrite from the Lodestar Prospect, Newfoundland, Canada. Can. Miner. 2003,41, 353–364. [CrossRef]
24.
Woodhead, J.D.; Hellstrom, J.; Hergt, J.M.; Greig, A.; Maas, R. Isotopic and Elemental Imaging of Geological Materials by Laser
Ablation Inductively Coupled Plasma-Mass Spectrometry. Geostand. Geoanal. Res. 2007,31, 331–343. [CrossRef]
25.
Ulrich, T.; Kamber, B.S.; Jugo, P.J.; Tinkham, D.K. Imaging Element-Distribution Patterns in Minerals by Laser Ablation-
Inductively Coupled Plasma-Mass Spectrometry (La-Icp-Ms). Can. Miner. 2009,47, 1001–1012. [CrossRef]
26.
Rittner, M.; Muller, W. 2D Mapping of La-Icpms Trace Element Distributions Using R. Comput. Geosci.
2012
,42, 152–161.
[CrossRef]
27.
Paul, B.; Paton, C.; Norris, A.; Woodhead, J.; Hellstrom, J.; Hergt, J.; Greig, A. Cellspace: A Module for Creating Spatially
Registered Laser Ablation Images within the Iolite Freeware Environment. J. Anal. At. Spectrom. 2012,27, 7–76. [CrossRef]
28.
Paul, B.; Woodhead, J.D.; Paton, C.; Hergt, J.M.; Hellstrom, J.; Norris, C.A. Towards a Method for Quantitative La-Icp-Ms Imaging
of Multi-Phase Assemblages; Mineral Identification and Analysis Correction Procedures. Geostand. Geoanal. Res.
2014
,38, 253–263.
[CrossRef]
Minerals 2023,13, 1049 13 of 13
29.
Ubide, T.; McKenna, C.A.; Chew, D.M.; Kamber, B.S. High-Resolution La-Icp-Ms Trace Element Mapping of Igneous Minerals;
In Search of Magma Histories. Chem. Geol. 2015,409, 157–168. [CrossRef]
30.
A, C.; Wang, Y.; Ren, J.; Bao, G. Disintegration of the Wanbaogou Group and Discovery of Early Cambrian Strata in the East
Kunlun Area. Geol. China 2003,2, 199–206.
31.
Zhou, Z.; Liao, Z.; Ma, T.; Yuan, Y. Study on the Genetic Mechanism and Material Source of Sanchakou Nephrite Deposit in East
Kunlun. Contrib. Geol. Miner. Resour. Res. 2006,3, 195–198.
32.
Paton, C.; Hellstrom, J.; Paul, B.; Woodhead, J.; Hergt, J. Iolite: Freeware for the Visualisation and Processing of Mass Spectrometric
Data. J. Anal. At. Spectrom. 2011,26, 2508–2518. [CrossRef]
33.
Andrut, M.; Gottschalk, M.; Melzer, S.; Najorka, J. Lattice Vibrational Modes in Synthetic Tremolite-Sr-Tremolite and Tremolite-
Richterite Solid Solutions. Phys. Chem. Miner. 2000,27, 301–309. [CrossRef]
34.
Jovanovski, G.; Makreski, P.; Kaitner, B.; Boev, B. Silicate Minerals from Macedonia. Complementary Use of Vibrational
Spectroscopy and X-Ray Powder Diffraction for Identification and Detection Purposes. Croat. Chem. Acta
2009
,82, 363. [CrossRef]
35.
Lei, C. The Genesis of the Xiaozaohuo Nephrite Deposit in Eastern Kunlun Orogenic Belt. Ph.D. Thesis, China University of
Geosciences, Wuhan, China, 2016.
36.
Schmetzer, K.; Bank, H. Explanations of the Absorption Spectra of Natural and Synthetic Fe- And Ti-Containing Corundums.
Neues Jahrb. Für Miner. Abh. 1980,139, 216–225.
37.
Shurvell, H.F.; Rintoul, L.; Fredericks, P.M. Infrared and Raman Spectra of Jade and Jade Minerals. Internet J. Vib. Spectrosc.
2001,5, 4.
38.
Dai, L.; Jiang, Y.; Yang, M. Study on the Spectral Ldentification Characteristics of “Heiqing” and “Heibi”. Spectrosc. Spectr. Anal.
2021,41, 292–298.
39.
Makreski, P.; Jovanovski, G.; Gajovi´c, A. Minerals from Macedonia: XVII. Vibrational Spectra of some Common Appearing
Amphiboles. Vib. Spectrosc. 2006,40, 98–109. [CrossRef]
40. Farmer, V.C. The Layer Silicates. Monogr. Miner. Soc. 1974,4, 331–363.
41. Burns, R.G.; Roger, G.J.S. Infrared Study of the Hydroxyl Bands in Clinoamphiboles. Science 1966,153, 890–892. [CrossRef]
42. Strens, R.G.J. The Infrared Spectra of Minerals. Miner. Soc. Monogr. 1974,4, 305–330.
43.
Patterson, J.H.; O’Connor, D.J. Chemical Studies of Amphibole Asbestos. I. Structural Changes of Heat-Treated Crocidolite,
Amosite, and Tremolite from Infrared Absorption Studies. Aust. J. Chem. 1966,19, 1155–1164. [CrossRef]
44.
Ishida, K.; Hawthorne, F.C.; Ando, Y. Fine Structure of Infrared Oh-Stretching Bands in Natural and Heat-Treated Amphiboles of
the Tremolite-Ferro-Actinolite Series. Am. Miner. 2002,87, 891–898. [CrossRef]
45. Wong, J.Y.; Berggren, M.J.; Schawlow, A.L. Far-Infrared Spectrum of Al2O3:V4+.J. Chem. Phys. 1968,49, 835–842. [CrossRef]
46.
Douglas, J.G. Exploring Issues of Geological Source for Jade Worked by Ancient Chinese Cultures with the Aid of X-Ray
Fluorescence. In Scientific Research in the Field of Asian Art; Archetype Publications: London, UK, 2003; pp. 192–199.
47.
Meinert, L.; Dipple, G.; Nicolescu, S. World Skarn Deposits; Society of Economic Geologists: Littleton, CO, USA, 2005; pp. 299–336.
48.
Jia, R.; Jiang, T.; Zhu, Y.; Liu, J. Gemmological Characteristic of “Qinghua” Nephrite from Hetian, Xinjiang. J. Gems Gemmol.
2019,21, 54–58.
49. Roth, P. The Early History of Tremolite. Axis 2006,2, 1–10.
50.
Stoll, S.; Schweiger, A. Easyspin, a Comprehensive Software Package for Spectral Simulation and Analysis in Epr.
J. Magn. Reson. (1997) 2006,178, 42–55. [CrossRef] [PubMed]
51.
Lu, B. The Gemological Mineralogy and Spectroscopy of Nephrite Cat’s Eye and Serpentine Cat’s Eye from Shimian, Sichuan
Province, Southwest of China. Ph.D. Thesis, Shanghai University, Shanghai, China, 2005.
52.
Abduriyim, A.; Kitawaki, H.; Furuya, M.; Schwarz, D. “Paraíba”-Type Copper-Bearing Tourmaline from Brazil, Nigeria, and
Mozambique: Chemical Fingerprinting by La-Icp-Ms. Gems Gemol. 2006,42, 4–21. [CrossRef]
53.
Laurs, B.M.; Zwaan, J.C.; Breeding, C.M.; Simmons, W.B.; Beaton, D.; Rijsdijk, K.F.; Befi, R.; Falster, A.U. Copper-Bearing
(Paraiba-Type) Tourmaline from Mozambique. Gems Gemol. 2008,44, 4–30. [CrossRef]
54.
Gallagher, D.; Hong, X.; Nurmikko, A.; Bhargava, R.N. Optical Properties of Manganese-Doped Nanocrystals of Zns.
Phys. Rev. Lett. 1994,72, 416–419.
55.
Evans, B.D.; Stapelbroek, M. Optical Properties of the F+ Center in Crystalline Al
2
O
3
.Phys. Rev. B
1978
,18, 7089–7098. [CrossRef]
56. McClure, D.S. Optical Spectra of Transition-Metal Ions in Corundum. J. Chem. Phys. 1962,36, 2757–2779. [CrossRef]
57.
Keig, G.A. Influence of the Valence State of Added Impurity Ions on the Observed Color in Doped Aluminum Oxide Single
Crystals. J. Cryst. Growth 1968,2, 356–360. [CrossRef]
58. Luo, G.; Chen, W. Basic Crystallography and Mineralogy; Nanjing University Press: Nanjing, China, 1993; pp. 210–267.
59.
Sharma, K.B.N.; Moorthy, L.R.; Reddy, B.J.; Vedanand, S. Epr and Electronic Absorption Spectra of Copper Bearing Turquoise
Mineral. Phys. Lett. A 1988,132, 293–297. [CrossRef]
60.
Sherman, D.; Waite, T. Electronic Spectra of Fe
3+
Oxides and Oxide Hydroxides in the Near Ir to Near Uv. Am. Miner. Am. Miner.
1985,70, 1262–1269.
Disclaimer/Publisher’s Note:
The statements, opinions and data contained in all publications are solely those of the individual
author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to
people or property resulting from any ideas, methods, instructions or products referred to in the content.
