Investigation of the Mineralogical Composition and Origin Analysis of Black Jadeite

doi:10.21203/rs.3.rs-3608159/v1

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Investigation of the Mineralogical Composition and Origin Analysis of Black Jadeite

https://doi.org/10.21203/rs.3.rs-3608159/v1

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Analyzing black jadeite variety not only helps to distinguish it from the more common omphacite jadeite, but also helps to study the origin of jadeite by studying these special specimens. The basic gemological properties, mineral composition, structural characteristics, spectroscopic features, and color-causing mechanisms of black jadeite were studied through testing methods such as Polarizing microscope, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy. Research has shown that black Jadeite have columnar crystalloblastic texture, granular crystalloblastic texture, fibrous crystalloblastic texture, and fracture structures. The secondary minerals are black impurities, manifested as opaque irregular small dots, and their Raman spectra and X-ray diffraction show typical characteristics of a mixture of graphite and disordered graphite. Based on the distribution of graphite and disordered graphite mixtures, they exhibit varying degrees of light absorption, resulting in the formation of different shades of black, which is the color-causing factor of black jadeite. These carbonaceous substances are the result of the carbonization of mixed organic matter in the fluid during the metamorphic process, gradually forming dispersed graphite and disordered graphite, distributed in mineral crystals, the interstices between mineral crystals, mineral crystal fracture surfaces, and cataclastic texture, indicating a multi-stage metamorphic cause. The discovery of graphite in jadeite supports the hypothesis that jadeite protolith originated from the subduction process of the Neotethys Ocean, accompanied by the metasomatism and high-pressure metamorphism of olivinite.

Earth and environmental sciences/Solid earth sciences/Geochemistry

Earth and environmental sciences/Solid earth sciences/Geology

Earth and environmental sciences/Solid earth sciences/Mineralogy

Black Jadeite

Mineral Composition

Graphite-like Carbonaceous

Metamorphic Origin

According to the Chinese national standard (GB/T 16553 − 2017), Jadeite jades primarily comprise jadeite or other sodic (-calcic) clinopyroxenes, such as omphacite and kosmochlor, along with minor amounts of amphibole, albite, and chromite. Collectively, this category is known as "feicui" in Chinese. Jadeite exhibits a wide range of colors, not confined to just green and red. It can also manifest in hues of purple, white, and black. In contrast to traditional ink-black jadeite (Omphacite jadeite), black jadeite appears black under both reflected and transmitted light and its black color exhibits varying degrees of darkness, ranging from gray-black to deep black. Analyzing this unique variety of jadeite not only aids in distinguishing it from the more common omphacite jadeite but also facilitates research into the origins of jadeite through the study of these exceptional specimens.

Regarding the spectroscopic characteristics of black jadeite, Ouyang ^[1] discovered that the primary mineral component of black jadeite is jadeite. The black color in black jadeite arises from the complete absorption of light by internal dark inclusions, gas-liquid inclusions, and the green pyroxene composition band of jadeite particles. The black inclusions primarily consist of minerals like magnetite, pyrite, and anatase. In Qiu's study^[2], it was suggested that the presence of numerous thread-like and needle-like black substances in the microstructural defects of jadeite grains leads to the black color, but no reasonable explanation for their composition was provided. Yan^[3] attributed the black color of jadeite mainly to black impurities in the gaps between jadeite grains. According to research conducted by Mao^[4], it was proposed that the black inclusions within black jadeite cause significant light scattering, which reduces its transparency and results in a black appearance. However, Zheng et al.^[5–6] raised objections to this viewpoint. In their research, they determined that carbon is the primary factor responsible for the black appearance in black jadeite. The varying carbon content in different areas leads to varying degrees of darkness in the samples. In terms of the primary components of black jadeite, especially its internal black impurities, there has not been a clear presentation of explicit experimental data testing and analytical reasoning.

To address the aforementioned issues, this study employs a series of testing methods including Polarized light microscopy, X-ray diffraction (XRD), Fourier-transform Infrared spectroscopy (IR), Raman spectroscopy, and others. The objective of this study is to perform a thorough analysis of the mineral composition and the occurrence state of black impurities, as well as their composition, in black jadeite. The study seeks to elucidate the coloring mechanism of black jadeite and provide a thorough interpretation of the relevant mechanisms underlying its origin-related questions.

2.1 Sample selection

These black jadeites are sequentially numbered as JE1 to 6, as shown in Fig. 1. Black jadeite can be categorized into pure black, grayish black, and grayish white according to its coloration: Pure black jade generally has a relatively pure and evenly distributed color tone (JE-1, JE-4, JE-5). Grayish black jade has a slightly lighter color that is usually distributed unevenly (JE-2, JE-6). Grayish white black jade has a color similar to "incense ash" - the black tone is very light (JE-3).

JE-1 is characterized by its block-like raw black jadeite material with a coarse-grained structure. It exhibits several semi-open fractures, some of which are partially filled with secondary yellow substances. Notably, the secondary green jadeite areas have a consistent luster and share similar mineral particle size and structure with the black jadeite areas. JE-2 is a block-like raw black jadeite material with fine-grained structure. The white jadeite areas have larger mineral crystalline particles, while the gray-black areas correspond to the black jadeite, showing a finer crystalline texture. Black impurities are dispersed within the jadeite minerals, and the white jadeite is bonded by the black jadeite. The darker parts have larger particles, lower hardness, and poorer luster, likely composed of amphibole minerals, a common occurrence in jadeite. JE-3, on the other hand, is an unpolished raw black jadeite material that also exhibits a block-like structure with a coarse-grained texture. It features prominent and coarse cleavage surfaces, commonly referred to as "fly-wings" luster. JE-4 is a polished black jadeite piece with fine texture and high transparency. The overall appearance exhibits a cloud-like distribution of black jadeite with slightly reduced transparency in the black jadeite part, while the luster remains largely unchanged, showing a transitional edge. JE-5 is a polished black jadeite piece with fine texture and good transparency. The sample base is uniformly apple green, with a distributed appearance of black jadeite showing a disseminated structure. Similarly, transparency is slightly reduced in the black jadeite areas, while luster remains relatively consistent, and the edges show a transitional appearance. JE-6 is a polished black jadeite piece with fine texture and high transparency. The black jadeite displays a staining distribution with uneven color. The areas with darker color have reduced transparency, while those with lighter color maintain good transparency, resulting in a noticeable contrast.

Refractive index and relative density tests were conducted on the selected black jadeite samples using a refractometer and the hydrostatic weighing method, following the guidelines outlined in the Chinese national standard (GB/T 16553 − 2017). The results revealed relative densities of 3.336 g/cm³, 3.310 g/cm³, 3.326 g/cm³, 3.341 g/cm³, 3.336 g/cm³, and 3.326 g/cm³, respectively. Correspondingly, the refractive index of these samples falls within the range of 1.65 to 1.66, consistent with the theoretical values for jadeite's relative density and refractive index.

Figure1 Raw black jadeite material

In addition, The Hetian jade nephrite (named ‘qinghua’ in Chinese), originated from Xinjiang province of China, with similar characteristics to the black impurities in black jadeite as comparative samples to enhance the reliability of experiments and testing, as shown in Fig. 2. Furthermore, the black impurities in Hetian jade nephrite have been identified as graphite^[7]. HE-1 is a pendant made of Hetian jade nephrite. It is uniformly black in color, displaying a greasy luster, having fine texture, and poor transparency. The black areas exhibit consistent hues, with the black impurities distributed uniformly in an oriented manner. The transparency of the black portions is significantly lower than that of the white portions. HE-2 is another pendant made of Hetian jade nephrite. It is overall grey-black in color, displaying a greasy luster, having fine texture, and poor transparency. The black impurities are uniformly oriented in distribution, and the surface shows the presence of secondary product.

2.2 Experimental methods

2.2.1 Polarizing microscope analysis

Polarizing microscopes are primarily used to examine the optical properties of transparent minerals through techniques such as plane-polarized light, cross-polarized light, and convergent light. Under plane-polarized light, the focus is primarily on observing the mineral's morphology, cleavage, color, pleochroism, edges, and protrusions. When using orthogonal polarized light microscopy, the main observations involve extinction phenomena, interference patterns, and birefringence in minerals. Convergent light microscopy, on the other hand, is employed to determine the axial characteristics, optical properties, and observing dispersion types in heterogeneous mineral specimens.

In order to study the mineral composition, structural characteristics, and the occurrence state of black impurities in black jadeite, the selected samples were sectioned and some of them were prepared as thin sections for observation under a polarizing microscope. The polarizing microscope used was a Zeiss Axio Imager A2^[8].

2.2.2 X-ray diffraction analysis

X-ray powder diffraction (XRD) is a rapid and simple qualitative and quantitative analytical technique. It works by irradiating a crystalline material with X-rays to produce a diffraction pattern that corresponds to the spacing between lattice planes and relative intensities. Diffraction data in the form of spectra and peak intensities can then be used to identify the mineral phases present. As such, XRD is a common and powerful tool in mineralogy.

Samples of black jadeites (JE-1,JE-2,JE-3) and Hetian jade nephrite (HE-1) were tested. Initially, the samples were ground into powder finer than 200 mesh using a corundum mortar. The experimental instrument employed was a Shimadzu XRD-7000 X-ray diffractometer. Experimental conditions were set according to reference^[9]: CuKα radiation (λ = 1.5406 Å), graphite monochromator, NaI detector, operating voltage of 40 kV, current of 30 mA, step size of 0.02°/step, scan rate of 2°/min. The test results were processed using x'pert highscore plus 3.0 software.

2.2.3 Infrared spectroscopy

Infrared light is a type of electromagnetic wave with a wavenumber range of 1-12800 cm^− 1. In the field of gemology, the frequency range of fundamental vibrations is within 1500–4000 cm^− 1, which mainly represents the stretching and bending vibrations of the atomic bonds and can be used to identify the functional groups that may exist in the gemstones. The fingerprint region covers a wavenumber range of 400–1500 cm^− 1, which mainly represents the stretching and deformation vibrations of the atomic bonds and can be used to identify specific molecular structures in gemstones ^[10].

FTIR was performed with the reflection mode. For the infrared spectroscopy tests, samples JE-1 to 6 and HE-1 were selected. Among them, samples JE-1, JE-2, JE-4, JE-5, and HE-1 were tested at two points: one for the black portion and the other for another portion. Since sample JE-3 is predominantly gray-white, only one point in the gray-white portion was tested. Similarly, sample JE-6, which is entirely black, was tested at a single point in the black portion. The infrared spectroscopy was carried out using a Boen 29865 spectrometer with an analysis range of 4000 − 400 cm^− 1. The samples were scanned 32 times, and the resolution was set to 8 cm^− 1. The working conditions were at a room temperature of 20–22°C, working voltage of 220–240 V, frequency of 50–60 HZ, and power of 250 W. Background spectra were recorded with a gold-coated mirror with a 5 mm sample cap aperture, and sample spectra were recorded with the same sample cap.

2.2.4 Raman Spectroscopy

Laser Raman spectroscopy is a type of molecular co-scattering spectrum that occurs when laser photons interact non-elastically with gemstone molecules, resulting in a change of the original incident frequency. Due to the distinct chemical compositions and structural arrangements of different substances, various Raman spectral features are present. This allows for the detection of both intensity and frequency information from the scattered light in Raman spectra, which can be utilized for the purpose of substance determination and identification. In our test, Laser Raman testing was conducted using a Thermo Fisher Scientific DXR2xi confocal Raman microscope ^[11].

The test sample were mineral flakes milled from black jadeite and Hetian jade nephrite. The testing conditions were set as follows: excitation at 532 nm using an Ar⁺ laser with an output power of 10 mW, spectral scan range spanning from 50-4000 cm^− 1, and a vertical spot diameter of 0.7 µm.

3.1 Polarizing microscope

The results of single-polarized light and cross-polarized light analyses of black jadeite are shown in Fig. 3. Group 'a' represents the results of single-polarized light analysis, and group 'b' represents the corresponding results of cross-polarized light for the respective structures. Among these, '1', '2' and '3' are from sample JE-1, while the rest, '4' to '8,' come from samples JE-2 to JE-6, respectively. From Figures a1 and b1, automorphic jadeite crystals with numerous microscopic fractures can be observed. The black point-like impurities are distributed within the jadeite crystals and their micro-fractures. Figures a2 and b2 show crystal bending, nematoblastic texture, and cataclastic texture. The degree of automorphic jadeite crystals is evident, along with some crystal bending, indicating the influence of stress. Black impurities in the form of star-like points are distributed within the jadeite crystals and cataclastic texture, exhibiting uneven distribution. Figures a3 and b3 exhibit a structure resembling granular crystalloblastic texture and fragmented crystals. The automorphic degree of crystals is relatively poor, with black point-like impurities distributed between jadeite crystals and within cataclastic texture, but not inside the crystals themselves. From Figures a4 and b4, a structure resembling embedded grain-shaped crystal variations is observed. Crystals show high automorphic degree, and pyroxene-like cleavage is clearly visible. Black point-like impurities are distributed between jadeite crystals, rather than inside them. Figures a5 and b5 show prismatic and fibrous crystalloblastic texture as well as cataclastic texture. This indicates the presence of at least two generations of jadeite. The first generation of jadeite particles is relatively coarse, while later ones experienced fracturing to form the cataclastic texture. The black point-like impurities are concentrated within the cataclastic texture, but are not distributed within the highly automorphic jadeite crystals. Figures a6 and b6 show prismatic crystalloblastic texture and cataclastic texture, with a high degree of automorphic and the presence of a crystal surface fracture. This also suggests the presence of at least two generations of jadeite. The first generation of jadeite crystals is larger and has a higher automorphic degree, while later fracturing led to the formation of cataclastic texture. The black point-like impurities are distributed relatively evenly. Figures a7 and b7 display granular crystalloblastic texture and cataclastic texture. Some crystals exhibit a high automorphic degree and clear pyroxene cleavage. This indicates the presence of at least two generations of jadeite. The first generation of jadeite crystals is larger and has a higher automorphic degree, while later dynamic metamorphic processes led to the formation of cataclastic texture. The black point-like impurities are not distributed within the jadeite crystals themselves but are concentrated within the cataclastic texture. Figures a8 and b8 reveal automorphic jadeite mineral particles with pyroxene cleavage and microscopic fractures. The black point-like impurities are directionally distributed within the jadeite mineral, following the cleavage planes, exhibiting uniform particle sizes.

Figure 3 Polarizing microscopic test results of black jadeite: (a)-- single polarizing light; (b)-- orthogonal polarized light; '1' to '3'-- JE-1; '4' to '8' -- JE-2 to 6

The results of single-polarized light and cross-polarized light analyses of Hetian jade nephrite are shown in Fig. 4. Group 'a' represents the results of single-polarized light analysis, and group 'b' represents the corresponding results of orthogonal polarized analysis for the respective structures. Among these, '1' is from sample HE-1, while the rest comes from samples HE-2. Visually, the samples exhibit a felted interwoven texture with small mineral grains and poor automorphic degree. Irregular, dot-like, and clustered black impurities are observed to be enriched in the black areas, while they are sparsely distributed in the white areas. This phenomenon is also highly similar to black jadeite.

Figure 4 Polarizing microscopic test results of Hetian jade nephrite: (a)-- single polarizing light; (b)-- orthogonal polarized light; '1' - HE-1; '2' -- HE-2

3.2 X-ray diffraction

Figure 5 (a), (b), and (c) show typical X-ray diffraction peak patterns of jadeite. The characteristic diffraction peaks in the X-ray diffraction spectrum are sharp, indicating a high degree of crystallinity in the jadeite mineral, which is consistent with the observations under polarized light microscopy. It's worth noting that weak diffraction peaks are present at a 2θ angle of 26.5° in the X-ray diffraction patterns of samples JE-1 and JE-3 (indicated by the black arrows). These peaks correspond to the characteristic diffraction peaks of graphite. In contrast, Fig. 5 (d) primarily displays diffraction peaks associated with nephrite, with no detection of other minerals.

3.3 Fourier transform infrared spectroscopy

Through infrared absorption spectroscopy testing, the black jadeite samples exhibit an infrared absorption spectrum characteristic of jadeite, as shown in Fig. 6(a). The frequencies, quantities, and absorption intensities of the absorption bands are consistent with those of standard jadeite. In contrast, the infrared absorption spectrum of Hetian jade nephrite is shown in Fig. 6(b), demonstrating frequencies, quantities, and absorption intensities of absorption bands that are consistent with standard tremolite. Jadeite belongs to the pyroxene mineral group, and its infrared spectrum is primarily composed of vibration modes of Si-O single-chain units. The chemical formula for pyroxene minerals is XY[Z₂O₆], where:

X = (M2): Ca, Mg, Fe²⁺, Mn²⁺, Na, Li;

Y = (M1): Mg, Fe²⁺, Mn, Al, Fe³⁺, Cr³⁺, Ti⁴⁺, V³⁺;

Z = (T): Si, Al.

The pyroxene group minerals belong to the monoclinic or orthorhombic crystal system, with space groups including Si-O stretching vibration, O_t-Si-O_t stretching vibration, Si-O_b-Si bending vibration, Si-O bending vibration, and M-O stretching vibration. The infrared spectrum of pyroxene group minerals can be described in three ranges: 1200 − 850 cm^− 1, 750 − 600 cm^− 1, and 600 − 300 cm^{− 1 [12]}. The results of infrared absorption spectroscopy testing on black jadeite samples indicate that in the 1200 − 850 cm^− 1 range, which is the strongest Si-O vibration absorption region, there are 4–6 absorption bands related to Si-O_b-Si stretching vibration and O_t-Si-O_t stretching vibration^[13–14]. In the 800 − 600 cm^− 1 absorption range, there are 2–4 sharp absorption bands with weak to moderate intensity, attributed to Si-O_b-Si bending vibration. In the 600 − 400 cm^− 1 strong absorption range, the vibrations of M¹ and M² coordination sites dominate, involving the vibrations of metal cations and O²⁻, resulting in moderate to strong absorption. The corresponding infrared absorption spectra and vibration relationships of the black jadeite sample are shown in Table 1.

Table 1

Infrared absorption spectra and vibration relationships of the black jadeite sample
Sample	Mineral	Band frequency (cm^− 1)	District(cm^− 1)	Vibration relation
JE-2	jadeite	1160, 1070, 1047, 958, 861	1100 − 850	Si-O_b-Si Stretching vibration; O_t-Si-O_t Stretching vibration
		740, 667	750 − 600	Si-O_b-Si Bending vibration
		580, 530, 474	600 − 400	Si-O Bending vibration M-O stretching vibration

The infrared absorption spectroscopy results of Hetian jade nephrite indicate that the infrared vibrations of Si-O groups in the pyroxene structure include stretching and bending vibrations of Si-O and Si-O-Si, as well as stretching vibrations of O-Si-O. The stretching vibrations occur in the range of 600 cm^− 1 to 1200 cm^− 1, while the bending vibrations occur in the range of 400 cm^− 1 to 600 cm^− 1. The stretching vibrations can be divided into symmetric and antisymmetric stretching vibrations. The stretching vibrations of (Si₄O₁₁) include the antisymmetric stretching vibrations of Si-O-Si in the high-frequency region of 900 cm^− 1 to 1200 cm^− 1, stretching vibrations of O-Si-O, and stretching vibrations of Si-O, as well as the stretching vibrations of Si-O-Si and Si-O in the low-frequency region of 600 cm^− 1 to 800 cm^{− 1 [15]}. The corresponding infrared absorption spectra and vibration relationships of the Hetian jade nephrite sample are shown in Table 2.

Table 2

Infrared absorption spectra and vibration relationships of Hetian jade nephrite samples
Sample	Mineral	Band frequency (cm^− 1)	District(cm^− 1)	Vibration relation
HE-1	tremolite	1146, 1045, 995, 920	1200 − 900	Si-O།Si stretching vibration
		757, 685, 645	800 − 600	Si—O—Si and Si-O stretching vibration
		543, 508, 465, 417	600 − 400	Si-O Bending vibration M-Ostretching vibration

3.4 Raman spectroscopy

Characteristic observation points of black jadeite and Hetian jade nephrite were selected for observation, as shown in Figs. 7 and 8. Testing points '1' to '4' are from sample JE-1, points '5' to '8' are from sample JE-2, point '9' is from sample JE-3, points '10' to '12' are from sample JE-4, points '13' to '14' are from sample JE-5, and points '15' to '16' are from sample JE-6. Points 'A' to 'M' are from sample HE-1, while points 'N' to 'T' are from sample HE-2.The Raman spectroscopy results for both are presented in Fig. 9, where (a) and (c) represent the results for the typical white and black measurement points of JE-4 and HE-2, and (b) and (d) show the results for various measurement points of JE-1 to 6 and HE-1 to 2.

From the observation of Fig. 9(a), the Raman test results for point 10 (white area) and point 12 (black area) of sample JE-4 reveal that the main mineral in the sample is jadeite. In the black and white areas of sample JE-4, peaks are observed around 202 cm^− 1, 327 cm^− 1, 373 cm^− 1, 430 cm^− 1, 523 cm^− 1, 699 cm^− 1, and 1038 cm^− 1, showing characteristic Raman shifts associated with jadeite. The Raman shift peak around 1038 cm^− 1 is attributed to the symmetric stretching vibration of the Si-O tetrahedral group, while peaks around 699 cm^− 1 and 373 cm^− 1 correspond to the bending vibration bands of Si-O-Si^[16]. The peaks at 373 cm^− 1, 699 cm^− 1, and 1038 cm^− 1 are characteristic Raman peaks of jadeite. Laser Raman spectroscopy of graphite is highly sensitive to the integrity of its crystallinity. The peak at 1585 cm^− 1 corresponds to the Raman peak (G peak) of intact single-crystal graphite. When defects are present or the orderliness is reduced, Raman peaks around 1360 cm^− 1 and 2721 cm^− 1 (D peak) can appear in the Raman spectrum. These three characteristic absorption peaks are only present in the black areas ^[17–20].

Due to the sensitivity of laser Raman spectroscopy to the crystallinity and integrity of graphite, the ratio of the intensities of the D peak to the G peak can roughly characterize the orderliness of graphite. Based on Fig. 9(d), it can be observed that for most of the test points, the G peak is more prominent while the D peak is relatively weak. This indicates the presence of both crystalline graphite crystals and disordered graphite-like carbon in the black areas. The results suggest a mixture of these two forms of graphite, with a higher content of graphite than the disordered graphite-like carbon.

Furthermore, when the test points are located in the colorless areas (No.7, 10, 11, 14 and 15) of the black jade sample, the Raman shifts of jadeite are observed. Conversely, when the test points are in the black areas (No.1, 2, 3, 4, 5, 6, 8, 9, 12, 13 and 16) of the black jade, Raman shifts near 1360 cm^− 1, 1585 cm^− 1, and 2721 cm^− 1 appear in the results, indicating the presence of jadeite, graphite, and disordered graphite-like carbon in a mixture.

According to the Raman test results for point S (black area) and point T (white area) of Hetian jade, as shown in Fig. 9 (c), the main mineral in sample HE-2 is tremolite. The black and white positions of sample HE-2 both exhibit Raman shifts around 225 cm^− 1, 675 cm^− 1, and 1060 cm^− 1, which are characteristic peaks of nephrite minerals, indicating that they are composed of nephrite minerals. The peaks at 931 cm^− 1, 1030 cm^− 1, and 1060 cm^− 1 represent Si-O stretching vibrations in nephrite minerals, while 675 cm^− 1 corresponds to Si-O-Si stretching vibrations, and 530 cm^− 1 corresponds to Si-O bending vibrations^[21]. Unlike the white areas, the black areas also exhibit Raman shifts near 1360 cm^− 1, 1585 cm^− 1, and 2721 cm^− 1, indicating the presence of both crystalline graphite and disordered graphite-like carbon. The results suggest a mixture of these two forms of graphite in the black areas.

Similarly, in Fig. 9 (d), when the test points are located in the colorless areas (No.B, D, F, H, J, L, N, O, R and T) of the Hetian jade, the Raman shifts correspond to nephrite minerals. Conversely, when the test points are in the black areas (No.A, C, E, G, I, K, M, Q and S), Raman shifts near 1360 cm^− 1, 1585 cm^− 1 and 2721 cm^− 1 are observed, indicating the presence of nephrite minerals, graphite, and disordered graphite-like carbon in a mixture. It is noteworthy that point P in the Hetian jade does not exhibit Raman shifts corresponding to nephrite minerals but only shows shifts related to graphite and disordered graphite-like carbon, suggesting a high content of carbonaceous material, mainly graphite and disordered graphite-like carbon.

4.1 Discussion on color factors

The black, dot-like impurities found in black jadeite consist of a blend of graphite and disordered graphitic carbon. They are located within mineral cleavage surfaces, mineral crystals, the interstices between mineral crystals, mineral crystal fracture surfaces, and cataclastic texture. This presence leads to an overall reduction in the transparency of jadeite samples. Depending on the distribution of these impurities, they exhibit varying levels of light absorption, resulting in the formation of different shades of black and contributing to the creation of black jadeite.

4.2 Discussions on the causes of jadeite

Generally, the formation of jadeite minerals generally undergoes two stages: the lithogenesis stage, which forms jadeite rocks with large crystal grains, loose structure, high self-shaping, and mostly white in color. However, the quality of these rocks is far from that of gem-quality jade. The second stage, the jadeite formation stage, involves geological processes acting on jadeite rocks formed during the lithogenesis stage. This includes dynamic metamorphism and hydrothermal metasomatism, which greatly improves the texture, color, and transparency of the jadeite rocks, resulting in the formation of jadeite^[22].

Graphite is a carbonaceous mineral that is widely distributed in nature and can be stable within a wide range of temperatures. It is mainly formed through the metamorphism of organic or inorganic carbonaceous substances, or by crystallization through C-H-O hydrothermal processes^[23].As for the source of the formation of graphite-like carbonaceous materials, many scholars have discovered fluid inclusions in jadeite, with methane being the CH₄^[24–25] shown in Fig. 10. CH₄ is also generated during the formation process of primary jadeite ^[26].

Jadeite is a mineral devoid of carbon. Within jadeite, the only substance identified as a source of carbon is fluid inclusions predominantly composed of CH₄. This observation lends support to the theory that Jadeite rocks typically result from the fluid metasomatism of ultrabasic rocks under high-pressure conditions in subduction zones^[27–31].

Black jadeite exhibits the presence of graphite-like materials, commonly found in mineral crystals, the interstices between mineral crystals, mineral crystal fracture surfaces, and cataclastic texture. Furthermore, the presence of graphite can be observed in jadeites from different generations. As a result, we can postulate that these graphitic substances originate from CH₄ through multi-stage metamorphic processes, indicating that the formation of black jadeite is a result of multi-stage metamorphic processes.

The primary mineral in black jadeite is jadeite, mainly exhibiting columnar crystalloblastic texture, granular crystalloblastic texture, fibrous crystalloblastic texture, radial crystalloblastic texture, and cataclastic texture. The secondary minerals in jadeite are graphite and disordered graphite mixtures. This presence leads to an overall reduction in the transparency of jadeite samples. Based on the distribution of graphite and disordered graphite mixtures, they exhibit varying degrees of light absorption, resulting in the formation of different shades of black, which is the color-causing factor of black jadeite.

The discovery of graphite in black jadeite lends support to the hypothesis that primary jadeite originates from the subduction process of the Neo-Tethys Ocean, accompanied by metasomatism of peridotites and high-pressure metamorphic events. Graphite and disordered graphite mixtures are located within mineral cleavage surfaces, mineral crystals, the interstices between mineral crystals, mineral crystal fracture surfaces, and cataclastic texture. The presence of Graphite and disordered graphite mixtures in black jadeite reveals the multi-stage genesis of jadeite.

Data curation, WX; Investigation, MT; Methodology, ZC; Writing – original draft, FG; Writing – review & editing, ZZ.

Data Availability

The data used to support the findings of this study are available from the corresponding author upon request.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Funding Statement

No funding was used in this study.

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No competing interests reported.

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Investigation of the Mineralogical Composition and Origin Analysis of Black Jadeite

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Abstract

Figures

1. Introduction

2. Sample selection and experimental methods

2.1 Sample selection

2.2 Experimental methods

2.2.1 Polarizing microscope analysis

2.2.2 X-ray diffraction analysis

2.2.3 Infrared spectroscopy

2.2.4 Raman Spectroscopy

3. Results

3.1 Polarizing microscope

3.2 X-ray diffraction

3.3 Fourier transform infrared spectroscopy

3.4 Raman spectroscopy

4. Discussion on color factors and causes of jadeite

4.1 Discussion on color factors

4.2 Discussions on the causes of jadeite

5. Conclusion

Declarations

References

Additional Declarations

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