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Article

Mineralogy and Geochemistry of “Laoshan Jade” from Shandong Province, China: Implications for Petrogenesis

by
Xiaomin Yu
1,
Yingxin Liu
1,* and
Chuqi Cao
2
1
School of Gemmology, China University of Geosciences, Beijing 100083, China
2
Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100044, China
*
Author to whom correspondence should be addressed.
Crystals 2022, 12(2), 243; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12020243
Submission received: 31 December 2021 / Revised: 5 February 2022 / Accepted: 7 February 2022 / Published: 11 February 2022
(This article belongs to the Special Issue Gem Crystals)
Browse Figures
Versions Notes

Abstract

:
“Laoshan Jade” is located in the Yangkou area of the Sulu UHP metamorphic belt. This is the first time a systematic research study is performed on its conventional gemological characteristics, mineral compositions, geochemical characteristics, and petrogenesis using a polarized light microscope, an electron probe microanalyzer (EMPA), an X-ray fluorescence spectrometer (XRF), and a Raman spectrometer. The gemological characteristics of “Laoshan Jade” are consistent with serpentine jade. It can be named serpentinite, mainly composed of serpentine (antigorite), chlorite (clinochlore), and magnetite. Some samples contain magnesite and chromite. Only small amounts of unaltered forsterite, chrysolite, and diopside can be found in poor-quality serpentine jade. The protolith of “Laoshan Jade” is metamorphic peridotite. Antigorite is altered from olivine. Clinochlorite is altered from the diopside. Disseminated magnetite is the metamorphic product. Unaltered olivine and diopside belong to protolith. Chromite with zonal texture also belongs to protolith. The average temperature and pressure of its core are calculated to be 1348 °C and 3.1 GPa, which indicates that the protolith comes from the mantle asthenosphere. The formation temperature of its edge is lower than 500 °C, with metamorphic origin. XRF experiments show that “Laoshan Jade” samples are relatively rich in Mg and more depleted in fusible elements (Al, Ca) than the original mantle peridotite, indicating that serpentinite protolith has undergone a certain degree of partial melting. Combined with EPMA results, the findings of this study reveal that protolith belongs to the depleted mantle peridotite in the subduction zone, partially melted in the mantle wedge, and reacted with subduction zone fluid. Pyroxene is altered into chlorite, olivine is altered into serpentine, and magnet is generated. The edge of chromite in the protolith is altered by the iron-rich fluid into magnetite. Finally, serpentinite is formed.

1. Introduction

Jade, as a symbol and representative of beautiful things and noble morality, has been deeply cherished by the Chinese people since ancient times. The jade culture has also become an indispensable part of Chinese traditional culture, and it still affects people’s lives. In China, jade is a mineral aggregate including jadeite, nephrite, serpentine jade, chalcedony, quartzite, agate, turquoise, etc., which has properties of beauty, durability, and rarity. Since the same material of jade often has different characteristics in different origins, in China, many jades have been named after their origins, such as “Hetian Jade”, “Xiuyan Jade”, “Taishan Jade”, etc.
The jade material in this study is a type of serpentine jade that belongs to serpentinite, whose main constituent minerals are serpentine including antigorite, lizardite, and chrysotile. There are numerous deposits of serpentine jade in China [1], New Zealand [2], the USA [3,4], South Korea [5], Mexico [6], etc. Therefore, many studies have reported their chemical compositions [7,8,9,10,11,12,13,14,15,16,17,18,19,20], crystal structures [9,11,14,15,18,19], spectral characteristics [7,8,9,10,11,12,13,14,15,18], and coloration mechanisms [10,13,14,15,16].
In this study, the serpentine jade is studied, which was discovered in the Yangkou area of Laoshan Mountain in Qingdao, Shandong Province, and has been mined and appreciated for hundreds of years and used as an ornamental stone. It is called “Laoshan Lvshi” in Chinese locally. However, there has been no study of this jade in the English literature before this article. Only a few Chinese articles mentioned its historical culture, texture, structure, and appreciation value [21,22]. Therefore, this article first conducted systematic gemological, mineralogical, and petrological tests on this jade to determine its gemological characteristics, mineral compositions, geochemical characteristics, and petrogenesis, using a polarized light microscope, EMPA, XRF, and Raman spectrometer, and then renamed it “Laoshan Jade”, which enriched the study of Chinese jade. In addition, the Yangkou area, where “Laoshan Jade” is located, is in the Sulu ultrahigh-pressure (UHP) metamorphic belt, which is a typical continental collision zone, with mafic–ultramafic intrusions developed [23,24,25,26]. It has a certain correlation with the petrogenesis of “Laoshan Jade”.

2. Geological Background

The “Laoshan Jade” deposit is located in the Sulu UHP metamorphic zone, the eastern extension of the Qinling–Dabie orogenic belt, east-central China (Figure 1), which is a UHP metamorphic belt formed by collision and deep subduction between Yangtze Plate and North China Craton during Early Mesozoic Triassic. Sulu UHP metamorphic belt follows the NNE–SSW trend, starting from the East China Sea of Jiangsu in the south and reaching Weihai, Shandong, in the north, with a width of about 180 km and a length of about 750 km [25]. It is connected to North China Craton by Tanlu Fault and Yantai–Wulian Fault in the north, and connected to Yangtze Continent by Jiashan–Xiangshui Fault in the south [24].
Yangkou area, where the mine is located, is in the southern part of Jiaodong Peninsula, about 50 km away from the urban area of Qingdao, Shandong Province. It is located in the middle of the Sulu UHP metamorphic belt. The main exposed rocks are ultrabasic rocks (including serpentinite and serpentinized peridotite), eclogite, metagabbro, and wall rock granite gneiss as a part of the metamorphic belt [25,26]. The ultrabasic rock blocks are distributed in belts with different scales [23] and in abrupt contact with granite gneiss. The “Laoshan Jade” deposit is part of the Yangkou ultrabasic rock, which is found southwest of the Yangkou area. There are two ore bodies distributed in a belt shape, one is eastward and the other is southeastward, extending from land to the Yellow Sea [22].

3. Samples and Methods

3.1. Samples

A total of 12 samples were collected from jade mined by local people in this study, all from the Yangkou Bay of Laoshan District, Qingdao, Shandong Province. They were labeled from yk-001 to yk-012 consecutively. In total, 10 samples were selected to observe their regular gemological characteristics, i.e. color, refractive index, transparency, luster, and texture (Figure 2).
The color of “Laoshan Jade” is from green to dark green, distributed unevenly, with some black points and white minerals. The samples are cryptocrystalline or granular texture, massive or band structure, slightly transparent to opaque, waxy, or silky luster. The refractive index is 1.56–1.57, the Mohs hardness is 4.45–5.20, and the specific gravity is 2.56–2.71, which is consistent with the corresponding parameters of serpentine jade.

3.2. Methods

In total, 10 polished thin sections of serpentinite were analyzed for mineral composition and texture type in the China University of Geosciences, Beijing (CUGB), using Olympus BX51 polarizing microscope in transmitted light (Tokyo, Japan). The photomicrographs were taken using a digital camera.
Microanalysis of chemical composition was carried out at the Institute of Tibetan Plateau Research (ITP), Chinese Academy of Sciences (CAS), by JEOL JXA-8230 Electron Probe Microanalyzer (Tokyo, Japan), with 15 kV accelerating voltage, 1 × 10−8 A beam current, and 2 μm beam spot diameter, identical for all analyzed minerals. Standard samples adopted the national standard of silicate minerals. Since different minerals have different gray levels in backscattered electron images, they were chosen to analyze chemical compositions quantitatively and take backscattered electron (BSE) images.
Using the data measured by EPMA, the oxygen-atom method was applied to calculate the cation numbers of each element of different minerals. The valence-difference method was used to distinguish the valence states of iron. Since the total positive valence of cations and the total negative valence of anions in minerals should maintain balance, and the value of total FeO obtained by the EPMA regards Fe3+ as Fe2+, the total positive valence of cations in the formula must be lower than the theoretical positive valence. According to this difference, the amounts of Fe2+ and Fe3+ were further calculated to obtain the chemical formula of each mineral.
Nine samples were selected and ground in the grinding lab of CUGB, and 200 mesh powders were obtained for X-ray fluorescence (XRF) measurement after cleaning and drying. The major elements of samples were collected in the Beijing Beida Yanyuan microstructure analytical technology lab, using the Rigaku ZSX Primus II wavelength-dispersive XRF spectrometer (Tokyo, Japan). Samples were melted with lithium metaborate, and elements from Na to U were detected. The analysis accuracy is better than 1%.

4. Results

4.1. Petrographic Characteristics

4.1.1. Texture and Compositions

Under a polarizing microscope in transmitted light, the tested samples show great textural and mineral composition variation. Three types of textures can be distinguished: (1) Lepidoblastic texture (Figure 3a,b). The mineral grains are mostly smaller than 0.1 mm in the form of small scales. The boundary and shape of grains cannot be distinguished under the polarized microscope. The macroscopic appearance of jade with lepidoblastic texture is fine, so it is the most important texture. (2) Foliaceous-lamellar crystalloblastic texture (Figure 3a,b). Some mineral grains are flaky and leaf-like, about 0.15–1 mm, often accompanied by lepidoblastic texture. (3) Granoblastic texture (Figure 3c). Some minerals in yk-009 and yk-010 samples are granular, with 0.5–1.0 mm larger grain sizes, which may be the morphology of the protolith before metamorphism. The macroscopic appearance of jade with this texture is poorer.
According to the morphology of each mineral (Figure 3), the shapes of serpentine can be divided into three types: flaky, leaf-like, and granular, with differently sized pseudomorphs of olivine (Figure 3a–c). The grain size of the flaky serpentine is the smallest, often smaller than 0.1 mm. The leaf-like and granular serpentines with pseudomorphs of olivine are larger, with sizes of 0.15–1 mm and 0.5–1 mm. Some chlorite minerals are idiomorphic–hypidiomorphic flaky (Figure 3d), and the others are stumpy, with pseudomorphs of pyroxene (Figure 3e). The particle size is approximately 0.2–0.4 mm. Opaque minerals are subrounded (Figure 3f) or disseminated (Figure 3d,e). Magnesite is xenomorphic granular and distributed in serpentine, with a larger particle size of about 0.3–1 mm (Figure 3g). In a few samples, olivine has a hypidiomorphic granular morphology, and some edges are serpentinized (Figure 3h). Pyroxene has a hypidiomorphic–xenoblastic columnar morphology, and part of that is severely altered (Figure 3i).

4.1.2. BSE Observations

Combined with the EPMA data, the main mineral in the observed samples is serpentine from BSE images. A small number of other minerals can also be detected, such as chlorite, the spinel group minerals of magnetite and chromite, pyroxene, and olivine. Serpentine has a small grain size and fuzzy boundary (Figure 4a). Chlorite is idiomorphic–hypidiomorphic flaky (Figure 4b). Magnetite is distributed among serpentine in the heterogeneous disseminated form (Figure 4c). Chromite is idiomorphic–hypidiomorphic granular, with more regular morphology and obvious zonal texture. The core has a higher grayscale, and the edge has a lower grayscale (Figure 4d,e), indicating that there are certain differences in the chemical composition. In addition, most olivine and pyroxene have been altered completely (Figure 4f–h); only some residual olivine and pyroxene are found in yk-012, which can be used as the basis to judge the protolith before metamorphism.
Combined with observations under a polarized microscope, it can be deduced that olivine, pyroxene, and the subrounded chromite are residual minerals of the protolith. When metamorphism occurred, chlorite was first formed from pyroxene. Then, serpentinization occurred to form different shapes of serpentine, while disseminated magnetite was formed later than serpentine.

4.2. Electron Probe Microanalysis

4.2.1. Serpentine

To obtain the main chemical compositions of serpentine, 37 points of EPMA data were tested (Table S1). The content of MgO is between 37.61 wt.% and 40.26 wt.%, 39.26 wt.% on average, which is slightly lower than the ideal value of 43.6 wt.% in serpentine. The average content of SiO2 is 43.40 wt.%, varying between 40.97 wt.% and 44.72 wt.%, which is roughly in line with the ideal value of 44.10 wt.%. The calculated cation numbers are shown in Table S2, and the chemical formula of serpentine is (Mg2+5.306–5.708Fe2+0.066–0.298Mn2+0.001–0.008Ni2+0.004–0.024Cr3+0–0.060Al3+0.003–0.265)[Si3.897–4.168O10](OH)8, roughly similar to the ideal serpentine chemical formula (Mg6[Si4O10](OH)8). It is obvious that there is a phenomenon of isomorphism in serpentine, such as Fe2+, Cr3+, Ni2+, and Al3+ replacing Mg2+, which may be the reason that MgO content in the sample is lower than the ideal value of serpentine.
As an altered mineral, serpentine can be altered from olivine and pyroxene. Mevel has demonstrated that Al and Ca concentrations in serpentine altered from olivine are relatively poorer, while Al and Cr are relatively richer in serpentine altered from pyroxene [28]. In our samples, the Al2O3 and CaO concentrations in most serpentine are less than 1 wt.% and 0.05 wt.%, respectively, and the Cr2O3 content is also low (Table S1). Therefore, these serpentines are mostly altered from olivine.

4.2.2. Chlorite

According to EPMA data obtained from 16 points (Table S3), the average MgO, Al2O3, SiO2, and TFeO concentrations of chlorite in “Laoshan Jade” are 32.76 wt.%, 14.56 wt.%, 32.29 wt.%, and 3.44 wt.%, respectively. There are some other minor components, e.g., 0.78–2.12 wt.% Cr2O3, 0.11–0.35 wt.% NiO, and a small amount of K2O, CaO, TiO2, Na2O, and MnO (mostly less than 0.10 wt.%). Remarkably, only two samples’ Al2O3 content is below 10.00 wt.%. Most of them are between 14.27 wt.% and 18.47 wt.%, which indicates that chlorite in “Laoshan Jade” is rich in Al and poor in Fe.
The calculated cation numbers of chlorite are given in Table S4. The chemical formula of chlorite is (Mg2+4.456–5.155Fe2+0.221–0.659Mn2+0–0.068Ni2+0.008–0.027Al3+0.443–1.012Cr3+0.060–0.162)[Si2.890–3.556, Al0.444–1.110)4O10](OH)8. The Fe-Mg-(Al+□) graph [29] (Figure 5) illustrates that chlorite in “Laoshan Jade” belongs to trioctahedral Mg chlorite (clinochlore).
Chlorite is widely distributed and can be formed in various geological environments [30]. It is generally believed that chlorite minerals altered from mudstones are richer in Al, while those altered from mafic rocks are relatively poorer in Al [31]. Usually, the n(Al)/(n(Al) + n(Mg) + n(Fe)) value is more than 0.35 in chlorite altered from mudstone, while that value is less than 0.35 in chlorite altered from mafic rock [32,33]. The n(Al)/(n(Al) + n(Mg) + n(Fe)) value of “Laoshan Jade” is less than 0.35 (Table S4), which indicates that chlorite is altered from mafic rock.

4.2.3. Spinel Group Minerals

Spinel group minerals belong to A2+B3+2O4 type oxides, often composed of solid solutions of various end-member components. Generally, they can be divided into spinel, magnetite, and chromite series according to trivalent cations Al3+, Fe3+, and Cr3+ [34].
It can be derived from Tables S5 and S6 that the phenomenon of isomorphism exists in spinel group minerals of “Laoshan Jade”. According to the calculated formulas (Table 1), spinel group minerals in “Laoshan Jade” can be roughly divided into two types—magnetite and chromite series.
Researchers have proposed that TiO2 content in magnetite can reach 12–16 wt.% in magmatic rocks, usually with titanomagnetite formed, while it is reduced in contact metasomatism or hydrothermal rocks, and the lowest in metasediments [35]. It is shown from BSE images (Figure 4) that most of the magnetite grains are irregular and disseminated, which means its formation is later than serpentine. The TiO2 content in magnetite (Table S5) is very low (0.01–0.17 wt.%). Therefore, it is speculated that in “Laoshan Jade”, magnetite is the secondary mineral, with a metamorphic origin.
The different EPMA data of chromite between cores and edges are listed in Table S5, which is in good agreement with the different grayscale BSE images (Figure 4c–e). The main components are Cr2O3 (47.30 wt.% on average) and TFeO (84.03 wt.% on average), respectively. The content of Cr2O3, Al2O3, and MgO decreases significantly from core to edge, and TFeO content increases dramatically, with increasing NiO content. The values of Fe3+/Fe2+, Cr# and Mg# are calculated, with Fe3+/Fe2+ = 0.092–0.220, Cr# = 54.59–76.03, Mg# = 34.23–55.64 in core and Fe3+/Fe2+ = 1.78–2.04, Cr# = 99.52–99.89, Mg# = 2.55–4.89 in edge. The calculated chemical formulas are given in Table 1.
According to the results listed in Table 1, the core is composed of minerals from the chromite series, which can be triangulated to determine its specific classification (Figure 6) [36]. The graph shows that four data points fall into the aluminum chromite area, and two data points fall into the chromite area. The edges fall in the ferrichromite area. According to the chemical formulas in Table 1, they are closer to magnetite.

4.2.4. Olivine

The detailed EPMA data of olivine is listed in Table S7, taking four oxygen atoms as the standard. The calculation results (Table S8) demonstrate Fe in olivine is basically Fe2+, and the Fo value of olivine (Fo = Mg# = 100 × Mg2+/(Mg2+ + Fe2+)) is 89.83–90.36. Calculated chemical formula is (Mg2+1.786–1.790Fe2+0.191–0.202Mn2+0.003–0.004Ni2+0.006–0.008)[Si0.992–1O4]. According to the classification of olivine, the Fo values of all six points are close to the boundary between forsterites and chrysolite. Yk-012-01, 02, 05, and 06 belong to forsterite.Yk-012-03 and 04 belong to chrysolite.

4.2.5. Pyroxene

Table S9 lists the detailed EPMA data of pyroxene. According to the calculated cation numbers and the value of En, Wo, Fs (Table S10), the classification graph of pyroxene (Figure 7) shows that most of the pyroxene in “Laoshan Jade” belong to diopside in clinopyroxene, and only one point falls in augite area. These calculation results (Table 2) are consistent with formulas of diopside. Moreover, it is found that the Mg# value of pyroxene in the sample is high (95.25–99.68), with a small variational range, indicating that the diopside in “Laoshan Jade” belongs to parts of the protolith and have not been altered strongly.

4.3. Whole-Rock Geochemistry

Test results of major elements in the whole rock of Shandong “Laoshan Jade” are listed in Table 3. It can be seen that all nine “Laoshan Jade” samples have a high loss on ignition (LOI) (10.79–14.48 wt.%), which characterizes the gaseous products (mainly H2O, CO2, etc.) during the thermal decomposition. Due to the fewer CO2 content in serpentinite, the LOI is mainly caused by the loss of H2O [18]. The average LOI (12.22 wt.%) is in good agreement with the standard 13 wt.% water content in ideal serpentine, indicating that all nine samples have a high degree of serpentinization. The lowest LOI is 10.79 wt.% in yk-012, which can be explained by its lower serpentinization degree, with the existence of a small amount of unaltered olivine and pyroxene (Figure 3 and Figure 4). The highest LOI is 14.48 wt.% in yk-006, which is caused by the high degree of serpentinization and the presence of magnesite (Figure 3g).
The main chemical components of “Laoshan Jade” can also be obtained from Table 3. The average SiO2 (37.86 wt.%) and MgO (34.94 wt.%) concentrations are lower than those in ideal serpentine (43.4 wt.% and 43.6 wt.%). There are two reasons for this result. One is the isomorphous replacement in serpentine, and the other is the complicated composition in “Laoshan Jade” samples, which are composed of serpentine, chlorite, magnetite, chromite, etc. The TFe2O3 and Al2O3 concentrations vary in different degrees (5.67–16.93 wt.% and 0.17–3.55 wt.%), which can be attributed to the different mineral compositions. For example, the TFe2O3 content in yk-003, yk-006, and yk-012 samples is relatively higher because of the presence of chromite, magnetite, and olivine (Figure 3).
The oxide content after subtracting LOI is given in Table 4. Hou et al. have supposed that serpentinization is basically an isochemical process, and petrochemical characteristics of serpentinite could represent that of protolith [19]. The average content of SiO2 is 43.24 wt.% (Table 4), which reveals that the protolith belongs to ultrabasic rock (SiO2 < 45 wt.%). According to the CaO-Al2O3-MgO graph [38] (Figure 8), the protolith in “Laoshan Jade” should be metamorphic peridotite.

5. Discussion

5.1. Types and Petrogenesis of the Protolith of “Laoshan Jade”

According to field observations and previous research [23], the geological occurrence of the “Laoshan Jade” rock mass shows that serpentinite is in abrupt contact with the surrounding granite gneiss, which is different from the metasedimentary rock, displaying layered conformable contact. Due to their mineral compositions, “Laoshan Jade” is named serpentinite, with a high degree of serpentinization. Together with the observation under the microscope, EPMA results, and test results for whole-rock geochemistry characteristics, it can be concluded that the protolith of “Laoshan Jade” belongs to ultramafic magmatic rock, peridotite.
ACM graph (Figure 8) shows that the protolith of “Laoshan Jade” is metamorphic peridotite. It is generally believed that the composition of the original mantle is lherzolite, which is transformed into dunite and harzburgite after partial melting [39]. The value of (Mg + TFe)/Si, MgO + TFeO can distinguish the type of metamorphic peridotite (Table 5) [40].
The value of (Mg + TFe)/Si of samples is 1.23–1.92, and the value of MgO + TFeO is 45.73–56.79% (Table 4), Most samples belong to harzburgite, yk-007 belongs to dunite, and yk-001, yk-003, yk-012 belong to lherzolite.
Based on olivine’s EPMA data, the concentrations of MgO, NiO, MnO, and Fo values are high, while CaO content is low. According to the CaO-Fo graph [41] (Figure 9), olivine in “Laoshan Jade” falls into the mantle peridotite area, indicating that the peridotite protolith is from the mantle.
Some accessory minerals in metamorphic rocks are from the protolith and relatively stable during the metamorphic process. Therefore, the study of accessory minerals can be used as an important basis to judge the type and evolution of the protolith.
The accessory minerals in “Laoshan Jade” samples are mainly magnetite and chromite (Figure 4). It can be clearly seen that the disseminated magnetite was formed in the later metamorphic process, while the idiomorphic granular chromite with zonal texture was formed earlier. Researchers believed that zonal texture in chromite formed by magma crystallization shows a trend of decreasing Cr# and increasing Mg# from core to edge [42,43]. However, the tendency in chromite of “Laoshan Jade” is indicating a reverse trend, with increased Cr# and decreased Mg#, which demonstrates the zonal texture of chromite is not formed by magma crystallization and differentiation. Previous studies have indicated that magnetite at the edge of chromite can be formed during the process of regional metamorphism, and it is the product of chromite alteration during the serpentinization process [44,45,46,47]. From the Cr-Al-Fe3+ graph of metamorphic facies [48] and metamorphic temperatures graph [46] of chromite in ”Laoshan Jade“, it can be inferred that cores fall in the mantle chromite area, indicating that chromite in the core with regular shape is of magma origin and belongs to protolith mineral, while magnetite in the edge was formed by the metamorphic alteration with a temperature lower than 500 °C (Figure 10).
Qi has proposed that total cation numbers in edges may be less than those in cores during alteration of the original chromite, which is attributed to the out-migration of Mg2+ and Al3+ [49]. Therefore, in order to maintain the balance of total electron valency, part of Fe2+ in original minerals should be oxidized to Fe3+, and the external Fe3+ needs to penetrate the internal chromite [49]. The EPMA results demonstrate that the Fe2O3 content (1.68–5.56 wt.%) in chromite core is much lower than that in edge (54.75–67.68 wt.%); thus, the core is not enough to provide all Fe3+ contents in Fe2O3 at the edge. Moreover, since chromite crystal is very stable, it is relatively difficult to change its chemical composition only by low-pressure and low-temperature serpentinization [50]. Combined with the fact that some magnetite was filled in the serpentine in “Laoshan Jade” samples (Figure 3), it is deduced that chromite was once altered by Fe-rich fluid during the serpentinization process in an environment with a high oxygen fugacity, where Fe3+ is much more than Fe2+ and is transferred to magnetite at the edge accompanied by the replacement between Fe in fluid and Al and Cr in chromite.
As a characteristic accessory mineral, chromite is a superior geothermometer, because its elemental composition is sensitive to physical and chemical conditions of the upper mantle during the crystallization process [51]. Due to its better resistance to metasomatism and corrosion, it is useful to explore the genetic information of the protolith by analyzing its elemental composition. In order to obtain its crystallization conditions, the following formulas were used to calculate temperature and pressure [52]:
P = 18.7 + 27.9 ( X Cr S p + X Fe S p ) ,
T = ( 4250 Y Cr S p + 1343 ) / ( ln K Cr 0 + 1.825 Y Cr S p + 0.571 ) ,
ln K Cr 0 = 0.34 + 1.06 ( Y Cr S p ) 2 ,
Y Cr S p = Cr / ( Cr + Al + Fe 3 + ) ,
where X Cr S p and X Fe S p , respectively, represent the mole fraction of Cr3+ and Fe2+ in chromite.
The calculated temperature and pressure results of the chromite core are presented in Table 6. The average crystallization temperature and pressure are 1348 °C and 3.1 GPa, respectively, which are similar to the temperature (1280–1350 °C) and pressure (3 GPa) conditions of the asthenosphere, indicating the protolith may be derived from the upper mantle asthenosphere.
Different graphs of chromite were used to determine the characteristics of the protolith. The relationship of Cr#-TiO2 [53] (Figure 11) indicates that chromite is from the depleted mantle peridotite. Furthermore, both Al2O3-TiO2 tectonic setting graph (Figure 12a) and Al2O3-Fe2+/Fe3+ protolith discrimination graph [54] (Figure 12b) demonstrate that chromite belongs to subduction zone peridotite.
It is generally accepted that peridotite originates from the upper mantle. Comparing the oxide content after deducting LOI with that of global primitive mantle peridotite [55], the average MgO content in “Laoshan Jade” samples is 39.92 wt.% (Table 4), higher than that in Table 7, with Al2O3 (1.78 wt.%) and CaO (0.40 wt.%) contents lower than those in Table 7. This phenomenon indicates that the protolith of “Laoshan Jade” belongs to the depleted mantle peridotite and has undergone a certain degree of partial melting, which is consistent with the results of Figure 11.
Based on the above analysis, it is deduced that the serpentinite protolith of “Laoshan Jade” belongs to peridotite, originated from the mantle wedge partially melted in the mantle wedge, which is consistent with the conclusions of a previous study [23].

5.2. Serpentinization Process

The Serpentinization process of peridotite from mantle wedge is usually related to the fluid released by the subducting plate [25]. At certain temperature and pressure conditions, large amounts of H2O and fluid migration elements were released from the subducted slab of the underlying Yangtze plate, metasomatized with the depleted peridotite. The serpentinite was formed.

5.2.1. Types of Serpentine

Antigorite, lizardite, and chrysotile are three types of serpentine. They can be distinguished by Raman spectra.
According to the research of Bahram [56], there are slight differences in the wavenumber positions of these spectral peaks for the three types of serpentine. Near 230 cm−1, the spectrum peak of antigorite is located at a lower wavenumber (224–230 cm−1), while the spectrum peak of lizardite is located at a medium wavenumber (229–231 cm−1), and the spectral peak of the chrysotile is at a higher wavenumber position (231–235 cm−1). Near 350 cm−1, there is no spectral peak for the antigorite, while there are irregular weak peaks in the lizardite, and the peak is more obvious for chrysotile. Near 390 cm−1, the peak of antigorite is at the lower wavenumber (377–382 cm−1), while the peak of lizardite is at the middle wavenumber (382–385 cm−1), and the peak of chrysotile is located at a higher wavenumber position (383–391 cm−1). Near 690 cm−1, the peak of antigorite is at a lower wavenumber position (681–688cm-1), the peak of lizardite is located at the middle wavenumber position (685–691 cm−1), and the peak of chrysotile is at the higher wavenumber position (689–691 cm−1). In addition, there are common peaks near 1050 cm−1 in antigorite, while chrysotile has a spectral peak near 1100 cm−1, and for lizardite, there is occasionally no peak.
The Raman spectra of the samples’ serpentine are shown in Figure 13. Four strong peaks are located near 230 cm−1, 380 cm−1, 690 cm−1, and 1050 cm−1. The main peaks and their functional group attribution are summarized in Table 8.
According to the statistical results in Table 8, the main spectral peaks of serpentine in the sample are mostly located at low wavenumber positions and have peaks near 1050 cm−1. Only the spectral peak of serpentine in yk-010 is mainly located at medium wavenumber position and is missing the peak near 1050 cm−1.
In addition, some irregular weak peaks were found and analyzed as follows: The weaker peak near 350 cm−1 in the yk-010 is attributed to the [SiO4] tetrahedral bending vibration, which is the characteristic peak of lizardite. The peak of 460 cm-1 is attributed to Si-O bending vibration. The weak peak of 520 cm−1 may be related to the deformation vibration of the Si-O tetrahedron and Al-O tetrahedron. The small peak of 630 cm−1 is attributed to the OH-Mg-OH conversion mode.
These results show that there is lizardite in the yk-010, and the serpentine of other samples belongs to the antigorite. The presence of chrysotile was not detected in samples.
In addition, lizardite contains more Al and Fe cations, while antigorite is richer in Si and poorer in Mg [57]. Most lizardites contain 38–40 wt.% SiO2 [58], and most antigorite minerals contain 42–45 wt.% SiO2 [59,60]. According to EPMA data (Table S1), the SiO2 content of serpentine is mostly between 42 wt.% and 45 wt.%.
In conclusion, most of the serpentine in the sample belongs to antigorite. Antigorite is the most common type of serpentine in the subduction zone [61].

5.2.2. Temperature of Serpentinization Process

In the subduction zone, the conversion between serpentine minerals is mainly controlled by temperature. Lizardite exists at a low temperature of 200 °C and can be transformed into chrysotile by heating. Antigorite stably exists in a high temperature above 300 °C and starts to be dehydrated at 400 °C [62]. According to the types of serpentine in the samples, the temperature of serpentinization can be preliminarily assessed.
Most of the serpentine minerals in “Laoshan Jade” are poor in Al and Ca, formed by alteration of olivine. Guo showed that the serpentinization of olivine has the strongest alteration at 300 °C and begins to weaken when the temperature reaches 350 °C [25].
Figure 3 reveals that a small amount of chlorite in the serpentinite is idiomorphic to hypidiomorphic, with a pyroxene pseudomorph, indicating that it forms earlier than antigorite. Because its crystal structure and composition are very sensitive to pressure, temperature, the composition of the whole rock, and physical–chemical properties of environments [63], chlorite is usually used as a geological thermometer to obtain the physical and chemical conditions during the crystallization process. Here, an empirical thermometer and interplanar spacing thermometer of chlorite were used to calculate its crystallization temperature. The formulas are as follows [64,65,66,67,68,69,70]:
T(°C) = 212AlⅣ+18 (AlⅣ is calculated by 14 oxygen atoms, same as below)
T(°C) = −61.92 + 321.98AlⅣ
T ( ° C ) = 319 [ Al Ⅳ + 0.1 [ Fe Fe + Mg ] ] − 69
T ( ° C ) = 212.4 [ Al Ⅳ − 0.44 [ Fe Fe + Mg − 0.34 ] ] + 17.5
T ( ° C ) = 212.4 [ Al Ⅳ − 0.24 [ Fe Fe + Mg − 0.163 ] ] + 17.5
d001(0.1 nm) = 14.339 − 0.1155AlⅣ − 0.02Fe2+
d001(0.1 nm) = 14.339 − 0.001T(°C)
It is obvious that calculation results of the empirical thermometer are relatively consistent (Table 9), while results of the interplanar spacing thermometer are relatively lower. Therefore, the crystallization temperature of chlorite is around 200 °C.
The BSE images (Figure 4) show that magnetite is disseminated in antigorite, indicating its formation time is later. Previous studies have demonstrated that magnetite begins to appear at high temperatures (>300 °C) [71,72], and there is no magnetite crystallized at low temperatures (<200 °C) [73,74].
In summary, the serpentinization process of “Laoshan Jade” serpentinite can be divided into the following three stages:
1. When the temperature was lower (around 200 °C), the fluid released from the subduction zone interacted with depleted mantle peridotite. Pyroxene was altered into chlorite, and serpentinization of olivine began to form lizardite.
2. As the subduction deepened, and the temperature increased (300–350 °C), the degree of serpentinization of olivine became strongest with the formation of antigorite. At the same time, magnetite began to crystallize. The Fe-rich fluid reacted with chromite in the protolith and formed the zonal texture of chromite.
3. At higher temperatures (>350 °C), serpentinization of olivine began to weaken, and serpentinite was finally formed.

6. Conclusions

“Laoshan Jade” is a type of serpentine jade, which can be named serpentinite. It is mainly composed of serpentine (antigorite), chlorite (clinochlore), and magnetite. Some samples contain magnesite and chromite. A small amount of unaltered forsterite, chrysolite, and diopside can even be found in the poor-quality serpentine jade.
Antigorite and clinochlore in “Laoshan Jade” are metamorphic products of olivine and pyroxene, respectively. Magnetite is crystallized during the serpentinization process. Residual forsterite, chrysolite, diopside, and chromite are protolith minerals, from metamorphic peridotite. The cause of the zonal texture of chromite was discussed. The average formation temperature and pressure of chromite’s core are 1347 °C and 3.3 GPa, close to the environment of the mantle asthenosphere, indicating that the protolith originated from the mantle asthenosphere. The formation temperature of its edge is lower than 500 °C, with metamorphic origin. The graph of chromite’s core shows that the peridotite protolith belongs to the depleted mantle peridotite in the subduction zone, consistent with the main elements analysis results of the whole rock of “Laoshan Jade”. These results reveal that the protolith of serpentinite had undergone a certain degree of partial melting. The serpentinization process of peridotite occurred in the mantle wedge. After three stages of serpentinization of peridotite, serpentinite finally formed.

Supplementary Materials

The following are available online at https://0-www-mdpi-com.brum.beds.ac.uk/article/10.3390/cryst12020243/s1, Table S1: Chemical compositions of serpentines in “Laoshan Jade” (wt.%), Table S2: Cation numbers based on 14 O of serpentine in “Laoshan Jade”, Table S3: Chemical compositions of chlorites in “Laoshan Jade” (wt.%), Table S4: Cation numbers based on 14 O of chlorites in “Laoshan Jade”, Table S5: Chemical compositions of spinel group minerals in “Laoshan Jade” (wt.%), Table S6: Cation number of each element of spinel group minerals in “Laoshan Jade”based on 4 oxygens, Table S7: Chemical compositions of olivine in “Laoshan Jade” (wt.%), Table S8: Cation number of each element of olivine in “Laoshan Jade” based on 4 oxygens, Table S9: Chemical compositions of pyroxene in “Laoshan Jade” (wt.%), Table S10: Cation number of each element of pyroxene in “Laoshan Jade” based on 4 oxygens.

Author Contributions

Conceptualization, X.Y. and Y.L.; Methodology, X.Y. and Y.L.; experimental analysis, X.Y. and C.C.; software, X.Y.; validation, X.Y., Y.L. and C.C.; formal analysis, X.Y.; investigation, X.Y and C.C.; data curation, X.Y.; writing—original draft preparation, X.Y.; writing—review and editing, X.Y., Y.L. and C.C.; supervision, Y.L. and C.C.; project administration, Y.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The content presented here was sourced from existing published literature, hence, this clause is not applicable.

Acknowledgments

We would like to extend our gratitude to the members of the Gem Research Laboratory of China University of Geosciences (Beijing) and Beijing Beida Yanyuan microstructure analytical technology lab for their help. Special thanks should be given to Jing Xie from the Institute of Tibetan Plateau Research (ITP), Chinese Academy of Sciences (CAS), for her assistance with EPMA.

Conflicts of Interest

The authors declare no conflict of interest.

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Crystals 12 00243 g001 550
Figure 1. Regional geological map of Sulu UHP metamorphic belt [27].
Figure 1. Regional geological map of Sulu UHP metamorphic belt [27].
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Figure 2. Photos of 10 “Laoshan Jade” samples.
Figure 2. Photos of 10 “Laoshan Jade” samples.
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Figure 3. Photomicrographs of “Laoshan Jade” (crossed-polarized light). (a,b) Lepidoblastic texture and foliaceous-lamellar crys-talloblastic texture, flaky and leaf-like serpentine; (c) Granoblastic texture, granular serpentine with the pseudomorph of olivine; (d) Chlorite and disseminated ferrous metal minerals; (e) Chlorite with the pseudomorph of pyroxene; (f) Ser-pentine and subrounded ferrous metal minerals; (g) Xenomorphic granular magnesite; (h) Hypidiomorphic granular ol-ivine; (i) Hypidiomorphic-xenoblastic columnar pyroxene.
Figure 3. Photomicrographs of “Laoshan Jade” (crossed-polarized light). (a,b) Lepidoblastic texture and foliaceous-lamellar crys-talloblastic texture, flaky and leaf-like serpentine; (c) Granoblastic texture, granular serpentine with the pseudomorph of olivine; (d) Chlorite and disseminated ferrous metal minerals; (e) Chlorite with the pseudomorph of pyroxene; (f) Ser-pentine and subrounded ferrous metal minerals; (g) Xenomorphic granular magnesite; (h) Hypidiomorphic granular ol-ivine; (i) Hypidiomorphic-xenoblastic columnar pyroxene.
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Crystals 12 00243 g004 550
Figure 4. BSE images of “Laoshan Jade”: (a) serpentine; (b) chlorite; (c) heterogeneous disseminated magnetite; (d) idiomorphic–hypidiomorphic chromite with zonal texture; (e) chromite and irregular band; (f) altered olivine and pyroxene; (g,h) altered pyroxene.
Figure 4. BSE images of “Laoshan Jade”: (a) serpentine; (b) chlorite; (c) heterogeneous disseminated magnetite; (d) idiomorphic–hypidiomorphic chromite with zonal texture; (e) chromite and irregular band; (f) altered olivine and pyroxene; (g,h) altered pyroxene.
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Crystals 12 00243 g005 550
Figure 5. Fe-Mg-(Al+□) classification graph of chlorite in “Laoshan Jade” [29].
Figure 5. Fe-Mg-(Al+□) classification graph of chlorite in “Laoshan Jade” [29].
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Figure 6. Classification graph of chromite [36] in “Laoshan Jade”: 1—ferrichromite; 2—ferrochromite; 3—picroalumochromite; 4—ferrochromopicotite; 5—ferroalumopicotite; 6—ferropicotite; 7—picotite; 8—alumopicotite; 9—chromopicotite; 10—alumochromite; 11—chromite; 12—errochromopicotite.
Figure 6. Classification graph of chromite [36] in “Laoshan Jade”: 1—ferrichromite; 2—ferrochromite; 3—picroalumochromite; 4—ferrochromopicotite; 5—ferroalumopicotite; 6—ferropicotite; 7—picotite; 8—alumopicotite; 9—chromopicotite; 10—alumochromite; 11—chromite; 12—errochromopicotite.
Crystals 12 00243 g006
Crystals 12 00243 g007 550
Figure 7. Classification graph of pyroxene in “Laoshan Jade” [37]: Wo—wollastonite; En—enstatite; Fs—ferrosilite; Di—diopside; He—hedenbergite; Au—augite; Pi—pigeonite; ClEn—clinoenstatite; ClFs—clinoferrosilite.
Figure 7. Classification graph of pyroxene in “Laoshan Jade” [37]: Wo—wollastonite; En—enstatite; Fs—ferrosilite; Di—diopside; He—hedenbergite; Au—augite; Pi—pigeonite; ClEn—clinoenstatite; ClFs—clinoferrosilite.
Crystals 12 00243 g007
Crystals 12 00243 g008 550
Figure 8. Al2O3-CaO-MgO graph in “Laoshan Jade” [38]: MC—mafic cumulate; UC—ultramafic cumulate; MP—metamorphic peridotite.
Figure 8. Al2O3-CaO-MgO graph in “Laoshan Jade” [38]: MC—mafic cumulate; UC—ultramafic cumulate; MP—metamorphic peridotite.
Crystals 12 00243 g008
Crystals 12 00243 g009 550
Figure 9. CaO-Fo graph of olivine [41].
Figure 9. CaO-Fo graph of olivine [41].
Crystals 12 00243 g009
Crystals 12 00243 g010 550
Figure 10. Cr-Al-Fe3+ graph of metamorphic facies [48] and metamorphic temperatures graph [46] of chromite in “Laoshan Jade”.
Figure 10. Cr-Al-Fe3+ graph of metamorphic facies [48] and metamorphic temperatures graph [46] of chromite in “Laoshan Jade”.
Crystals 12 00243 g010
Crystals 12 00243 g011 550
Figure 11. Cr-TiO2 discriminant graph of Chromite in “Laoshan Jade” [53].
Figure 11. Cr-TiO2 discriminant graph of Chromite in “Laoshan Jade” [53].
Crystals 12 00243 g011
Crystals 12 00243 g012 550
Figure 12. Discriminant graph of chromite [54] in “Laoshan Jade”: (a) Al2O3-TiO2 graph; (b) Al2O3-Fe2+/Fe3+ graph.
Figure 12. Discriminant graph of chromite [54] in “Laoshan Jade”: (a) Al2O3-TiO2 graph; (b) Al2O3-Fe2+/Fe3+ graph.
Crystals 12 00243 g012
Crystals 12 00243 g013 550
Figure 13. Raman spectra of serpentine samples in “Laoshan Jade”.
Figure 13. Raman spectra of serpentine samples in “Laoshan Jade”.
Crystals 12 00243 g013
Table
Table 1. Formulas of spinel group minerals in “Laoshan Jade”.
Table 1. Formulas of spinel group minerals in “Laoshan Jade”.
Spinel Group MineralNumberMineralFormula
MagnetiteYK-002-04magnetite(Fe2+0.946Mg2+0.037Mn2+0.005Ni2+0.014)(Fe3+1.989Ti4+0.003)O4
YK-002-05magnetite(Fe2+0.947Mg2+0.034Mn2+0.005Ni2+0.018)(Fe3+1.987Ti4+0.005)O4
YK-003-04magnetite(Fe2+0.920Mg2+0.017Mn2+0.012Ni2+0.020)(Fe3+2.009)O4
YK-006-12magnetite(Fe2+0.956Mg2+0.019Mn2+0.005Ni2+0.019)(Fe3+1.928Cr3+0.071)O4
YK-010-04magnetite(Fe2+0.970Mg2+0.019Mn2+0.003Ni2+0.015)(Fe3+1.983Cr3+0.003Ti4+0.005)O4
YK-012-21magnetite(Fe2+0.962Mg2+0.014Mn2+0.011Ni2+0.014)(Fe3+1.990Cr3+0.004Ti4+0.004)O4
The core of chromite.YK-003-06alumochromite(Fe2+0.650Mg2+0.338Mn2+0.008)(Cr3+1.187Al3+0.686Fe3+0.119Ti4+0.005)O4
YK-003-09alumochromite(Fe2+0.624Mg2+0.347Mn2+0.008)(Cr3+1.130Al3+0.746Fe3+0.128)O4
YK-003-11alumochromite(Fe2+0.614Mg2+0.375Mn2+0.009)(Cr3+1.036Al3+0.862Fe3+0.099Ti4+0.007)O4
YK-003-12alumochromite(Fe2+0.634Mg2+0.341Mn2+0.009)(Cr3+1.174Al3+0.687Fe3+0.139)O4
YK-006-08chromite(Fe2+0.440Mg2+0.552Mn2+0.007)(Cr3+1.421Al3+0.486Fe3+0.088)O4
YK-006-11chromite(Fe2+0.462Mg2+0.530Mn2+0.007)(Cr3+1.486Al3+0.468Fe3+0.042)O4
The edge of chromite.YK-003-10magnetite(Fe2+0.956Mg2+0.025Mn2+0.004Ni2+0.019)(Fe3+1.946Cr3+0.036Ti4+0.007)O4
YK-006-09magnetite(Fe2+0.934Mg2+0.036Mn2+0.023Ni2+0.017)(Fe3+1.806Cr3+0.173)O4
YK-006-10magnetite(Fe2+0.876Mg2+0.045Mn2+0.066Ni2+0.014)(Fe3+1.563Cr3+0.432)O4
Table
Table 2. Formulas of pyroxene in “Laoshan Jade”.
Table 2. Formulas of pyroxene in “Laoshan Jade”.
NumberFormula
YK-012-07(Ca2+0.957Mg2+1.015Fe2+0.018Fe3+0.008)[Si1.995O6]
YK-012-08(Ca2+0.962Mg2+0.995Fe2+0.029)[Si2.005O6]
YK-012-09(Ca2+0.910Mg2+1.059Fe2+0.003Mn2+0.006Fe3+0.027Al3+0.007)[Si1.982O6]
YK-012-17(Ca2+0.520Mg2+1.311Fe2+0.035Al3+0.003Cr3+0.003)[Si2.122O6]
YK-012-23(Ca2+0.957Mg2+1.006Fe2+0.024Mn2+0.004Fe3+0.003Al3+0.006)[Si1.994O6]
YK-012-24(Ca2+0.915Mg2+0.913Fe2+0.046Fe3+0.013Al3+0.032Cr3+0.023)[Si1.995O6]
Table
Table 3. Whole rock oxide contents in “Laoshan Jade” (wt.%).
Table 3. Whole rock oxide contents in “Laoshan Jade” (wt.%).
Sampleyk-001yk-002yk-003yk-004yk-005yk-006yk-007yk-010yk-012Average
SiO245.64036.22041.61036.09036.25036.80033.82036.06038.27037.862
MgO34.71035.55034.79034.50036.20037.69034.96035.31030.79034.944
Al2O30.3593.5501.3002.6501.3000.1720.9831.4202.3301.563
CaO0.0140.0410.0210.0600.0380.1550.0300.1192.7200.355
TFe2O35.67010.7908.59012.54012.7508.95016.93012.46013.11011.310
MnO0.1730.1830.1280.2250.1860.2390.1670.2030.2570.196
TiO20.0380.1030.4310.2180.0490.0000.0460.0500.0940.114
Cr2O30.0590.5950.5940.5340.5890.5020.5860.5330.6030.511
NiO0.2690.6660.5180.6840.6320.6660.5340.0000.6340.511
ZnO0.0910.1120.1940.1310.1960.1710.3100.1050.0740.154
Co3O40.0180.2590.0220.0250.0290.0230.0220.0240.0250.050
PbO0.0130.0000.0220.0220.0400.0740.0000.0120.0000.020
LOI12.83012.01011.96012.19011.59014.48011.37012.80010.79012.224
Total99.884100.079100.18099.86999.84799.92299.75899.09699.69899.815
TFe2O3 stands for total iron.
Table
Table 4. Oxide contents after deducting the loss on ignition in “Laoshan Jade” (wt.%).
Table 4. Oxide contents after deducting the loss on ignition in “Laoshan Jade” (wt.%).
Sampleyk-001yk-002yk-003yk-004yk-005yk-006yk-007yk-010yk-012Average
SiO252.42741.12747.16641.16141.07343.07038.26341.78643.04543.236
MgO39.87240.36639.43639.34841.01644.11239.55340.91734.63139.917
Al2O30.4124.0311.4743.0221.4730.2011.1121.6452.6211.777
CaO0.0160.0460.0230.0690.0430.1810.0340.1383.0590.401
TFe2O36.51312.2529.73714.30214.44610.47519.15414.43914.74612.896
MnO0.1990.2080.1450.2570.2110.2800.1890.2350.2890.224
TiO20.0440.1170.4890.2490.0550.0000.0520.0580.1060.130
Cr2O30.0680.6760.6730.6090.6670.5880.6630.6180.6780.582
NiO0.3090.7560.5870.7800.7160.7790.6040.0000.7130.583
ZnO0.1050.1270.2200.1490.2220.2000.3510.1220.0830.175
Co3O40.0200.2940.0240.0280.0320.0270.0250.0280.0290.056
PbO0.0150.0000.0250.0250.0450.0860.0000.0140.0000.023
Total100.000100.000100.000100.000100.000100.000100.000100.000100.000100.000
MgO/SiO20.7600.9820.8360.9560.9991.0241.0340.9790.8050.930
MgO + TFeO45.7351.3948.252.2254.0253.5456.7953.9147.9051.52
(Mg + TFe)/Si1.231.691.401.691.751.711.921.721.461.62
TFe2O3, TFeO, and TFe stand for total iron.
Table
Table 5. The main parameters of discrimination for protolith of metamorphic peridotite [40].
Table 5. The main parameters of discrimination for protolith of metamorphic peridotite [40].
The Main Parameters DuniteHarzburgiteLherzolite
(Mg + Fe)/Si2.1–1.91.90–1.551.65–1.35
MgO + TFeO
(%, deducting LOI)		59–5657–5052–45.5
Table
Table 6. Temperature and pressure of the chromite core in “Laoshan Jade”.
Table 6. Temperature and pressure of the chromite core in “Laoshan Jade”.
NumberMineralTemperature (°C)Pressure (GPa)
YK-003-06alumochromite1358.713.09
YK-003-09alumochromite1369.003.09
YK-003-11alumochromite1382.333.09
YK-003-12alumochromite1361.703.09
YK-006-08chromite1316.783.09
YK-006-11chromite1304.413.09
Average 1348.823.09
Table
Table 7. Oxide contents of the global primitive mantle peridotite (wt.%) [55].
Table 7. Oxide contents of the global primitive mantle peridotite (wt.%) [55].
OriginSiO2MgOAl2O3CaOTFeOTotal
Palme et al. (2003)45.436.774.493.658.198.41
Ringwood (1979)45.138.13.33.1897.6
Jagoutz et al. (1979)45.138.343.57.898.7
Wanke et al. (1984)45.636.84.13.57.597.5
Palme et al. (2003)46.235.54.84.47.798.6
Hart et al. (1986)4637.84.063.27
McDonough et al. (1995)4537.84.43.58.198.8
Allegre et al. (1995)46.1237.774.093.237.4998.7
TFeO stands for total iron.
Table
Table 8. The main peaks and functional group attribution of serpentine samples in “Laoshan Jade”.
Table 8. The main peaks and functional group attribution of serpentine samples in “Laoshan Jade”.
Serpentine230 cm−1390 cm−1690 cm−11050 cm−1
yk-0012313766821047
yk-0022293786821046
yk-0032313766831047
yk-0042313766831047
yk-0052303746831046
yk-0062303776821047
yk-0072323736831046
yk-010228382689
yk-0122313736811047
functional group attributionO-H-O group vibration[SiO4] Tetrahedral Deformation VibrationSi-Obr-Si symmetric stretching vibrationSi-Obr-Si anti-symmetric stretching vibration
Table
Table 9. Calculation results of chlorite temperatures in “Laoshan Jade”.
Table 9. Calculation results of chlorite temperatures in “Laoshan Jade”.
Number Empirical Thermometer (°C) Surface-Net-Spacing Thermometer (°C)
Cathelineau and Nieva (1985)Cathelineau (1988)Jowett (1991)Zane and Fyfe (1995)El-Sharkawy (2000)Battagla (1999)
YK-001-01204.14220.78212.99230.17209.25107.45
YK-001-04207.32225.61217.70233.59212.56108.88
YK-001-05208.80227.86219.87235.25214.14109.55
YK-002-02125.27101.0093.75152.84131.1562.90
YK-002-03232.54263.92255.29259.95238.43121.31
YK-003-03195.87208.22200.18222.98201.56101.76
YK-004-01223.64250.40241.96250.82229.39116.84
YK-004-02224.70252.01243.73251.37230.18117.91
YK-004-03207.10225.29217.08234.24212.82107.87
YK-005-02214.74236.88228.57241.89220.47111.96
YK-007-01186.33193.73185.75213.63192.1196.31
YK-007-03229.79259.74251.38256.48235.28120.58
YK-007-04223.64250.40242.17250.21229.06117.44
YK-012-18112.1381.0473.98139.64117.9655.82
YK-012-19152.41142.22137.36171.90153.9086.41
YK-012-20253.24295.35289.07272.92254.92134.25
Average200.10214.65206.93226.12205.20104.83
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Yu, X.; Liu, Y.; Cao, C. Mineralogy and Geochemistry of “Laoshan Jade” from Shandong Province, China: Implications for Petrogenesis. Crystals 2022, 12, 243. https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12020243

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Yu X, Liu Y, Cao C. Mineralogy and Geochemistry of “Laoshan Jade” from Shandong Province, China: Implications for Petrogenesis. Crystals. 2022; 12(2):243. https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12020243

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Yu, Xiaomin, Yingxin Liu, and Chuqi Cao. 2022. "Mineralogy and Geochemistry of “Laoshan Jade” from Shandong Province, China: Implications for Petrogenesis" Crystals 12, no. 2: 243. https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12020243

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