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Article

Manganese-Rich Chromite in Myanmar Jadeite Jade: A Critical Source of Chromium and Manganese and Its Role in Coloration

by
Yu Zhang
,
Guanghai Shi
* and
Jiabao Wen
School of Gemmology, China University of Geosciences, Beijing 100083, China
*
Author to whom correspondence should be addressed.
Crystals 2025, 15(8), 704; https://doi.org/10.3390/cryst15080704 (registering DOI)
Submission received: 28 June 2025 / Revised: 22 July 2025 / Accepted: 29 July 2025 / Published: 31 July 2025
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Abstract

Color is a primary determinant of the value of jadeite jade, but the petrological provenance of the chromogenic elements of jadeite jade remains uncertain. The characteristics of the associated chromite in Myanmar jadeite jade were systematically investigated through a series of tests, including polarized microscopy, microarea X-ray fluorescence spectroscopy (micro-XRF) mapping, electron probe microanalysis (EPMA), and backscattered electron (BSE) imaging. The results demonstrate that the chromite composition in Myanmar jadeite jade is characterized by a high concentration of Cr2O3 (46.18–67.11 wt.%), along with a notable abundance of MnO (1.68–9.13 wt.%) compared with the chromite from the adjacent Myitkyina peridotite. The diffusion of chromium (Cr) and manganese (Mn) in jadeite jade is accomplished by accompanying the metamorphic pathway of Mn-rich chromite → kosmochlor → chromian jadeite → jadeite. In the subsequent phase of jadeite jade formation, the chromium-rich omphacite veins generated by the fluid enriched in Ca and Mg along the fissures of kosmochlor and chromian jadeite play a role in the physical diffusion of Cr and Mn. The emergence of the lavender hue in jadeite is contingent upon the presence of a relatively high concentration of Mn (approximately 100–1000 ppmw) and the simultaneous absence of Cr, which would otherwise serve as a more effective chromophore (no Cr or up to a dozen ppmw). The distinctive Mn-rich chromite represents the primary origin of the chromogenic element Cr (green) and, perhaps more notably, an overlooked provider of Mn (lavender) in Myanmar jadeite jade.

1. Introduction

Jadeite jade is the most highly valued gemstone in the Orient, collectively known as Feicui in Chinese. Jadeite jade (or jadeitite) is a metamorphic rock, consisting predominantly of jadeite or other sodic (-calcic) clinopyroxenes (e.g., omphacite and kosmochlor), with minor amphibole, albite, and chromite [1,2,3]. Jadeite, the primary mineral composing jadeite jade, is an allochromatic mineral with the molecular formula NaAlSi2O6 and theoretical values of the chemical composition of SiO2 59.4 wt.%; Al2O3 25.2 wt.%; and Na2O 15.4 wt.% [4]. Jadeite jade exhibits a wide range of colors, including green, purple, white, black, brownish red, and yellow. Of these, green and purple are the two most distinctive and valuable varieties. The most aesthetically pleasing green hue observed in jadeite jade is designated as “imperial” green [5]. This particular coloration is regarded as the most valuable in jade, not only in Eastern contexts but also in Western ones. The purple hue of jadeite jade is frequently designated as the “spring color” in Chinese, also known as “violet”. In the English literature, it is frequently designated as “lavender” [5,6]. The price of jadeite jade has increased significantly in recent decades, as evidenced by the auction prices of “imperial green” and “lavender” jadeite jade [7]. Color is a primary determinant of the commercial value of jadeite jade, prompting considerable research on its causes.
Chemically, pure jadeite is white, and its color is derived from trace elements [5]. The color of most jadeite is attributed to the substitution of transition metal ions for the fundamental Al3+ and a minor quantity of Mg2+ in jadeite [7]. Following years of research, the cause of the vivid green jadeite jade color (commonly referred to as the “imperial” green or “emerald” color) (Figure 1a), as well as the petrological source and formation mechanism, has been largely elucidated. The source of the vivid green color in jadeite jade has long been identified as trivalent chromium (Cr3+) from chromite. This element replaces Al3+ in the M1 position in jadeite, resulting in the green color observed in the mineral [7,8,9,10,11,12,13]. A minimal quantity of Cr3+ is necessary to induce a vivid color, with higher concentrations of Cr3+ leading to greener jadeite [5,7]. Myanmar jadeite jade with an imperial green hue contains approximately 0.3 wt.% Cr2O3, with the color intensifying to an intense green or dark green at concentrations above 0.3 wt.% Cr2O3, and vice versa, attaining a light green or pale green hue [8].
Nevertheless, the cause of the coloration of purple (lavender) jadeite jade and the source of the color-causing substances have been debated in the scientific literature over the past few decades. Various color-causing mechanisms have been proposed on the basis of UV–Vis spectra, chemical analyses, and comparisons with similarly colored minerals. The following three views are the most prominent: (1) The purple coloration of jadeite jade is attributed to the presence of manganese, which migrates into the jadeite lattice in different valence states, thereby producing a purple color. Additionally, other trace metal elements, such as iron, titanium, magnesium, and vanadium, have been identified as influencing hue [5,14,15,16]. (2) The purple color of jadeite jade is thought to be caused primarily by intervalence charge transfer between Fe2+-Fe3+ ion pairs [6,17]. (3) Purple and blue-violet jadeite jade are believed to be associated with Ti3+ [18].
Over the past decade, testing techniques have facilitated significant advancements in the study of the genesis of purple jadeite jade color. Analytical techniques such as electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and electron paramagnetic resonance spectroscopy (EPR) have been instrumental in this progress. It is widely accepted that purple jadeite jades can be classified into two distinct colors: lavender and blue-violet (Figure 1b,c). The chromophores responsible for the two colors are not identical. In the case of blue-violet jadeite jade, which is blue-violet in color due to the charge transfer of Fe and Ti, the concentrations of Fe and Ti are markedly greater than those observed in white and lavender jadeite jade [19,20,21]. However, the Mn content in lavender jadeite jade is relatively high, predominantly in the Mn3+ state (as determined by EPR), and color saturation is correlated with the concentration of Mn3+ [19,20,21,22,23].
The petrological origin and formation mechanism of the color-causing elements in green jadeite have basically been clarified [7,8,9,10,11,12,13]. Green jadeite results from the diffusion of trivalent chromium (Cr3+) into the jadeite lattice after metasomatism occurs when jadeite-forming fluid infiltrates chromite. The replacement of Al3+ by Cr3+ at the M1 position in jadeite has been demonstrated to be responsible for the green color of jadeite. Furthermore, the intensity of the green color increases with the concentration of Cr3+ [5,7].
Nevertheless, the petrological origin of manganese in lavender jadeite jade remains undetermined. Generally, manganese (Mn) can become enriched in Mn-bearing minerals, which release Mn into the lattice of jadeite during metamorphism. Alternatively, mineralizing fluids may carry manganese and form lavender jadeite when they crystallize. Jadeite-forming materials have been found to incorporate marine sediments [24], which may be enriched in manganese (Mn). Previous researchers have focused on this source of Mn. However, all of these inferences are hypothetical and lack practical evidence. Among the more than 50 minerals related to jadeite [24], no manganese-rich minerals or rocks have been found. The origin of manganese remains a topic of dispute among jadeite rock scholars.
This study systematically investigated chromite in Myanmar jadeite jade and revealed manganese-enriched components. Chromium and manganese diffuse chemically along the following metamorphic pathway: Mn-rich chromite → kosmochlor → chromian jadeite → jadeite. Petrographic and chemical analyses reveal that this manganese-rich chromite provides the chromogenic elements responsible for the green (Cr) and lavender (Mn) colors of jadeite jade. This is the first time empirical evidence has been presented for the source of Mn in jadeite jade.

2. Materials and Methods

2.1. Selection and Preparation of Samples

The chromite found in jadeite jade and the surrounding rocks are relics of a protolith [24]. Green jadeite is closely associated with metasomatism between chromite and jadeite-forming fluid. However jadeite samples that retain residual chromite (black spots visible to the naked eye) are not common. Occasionally, chromite is observed in some green Myanmar jadeite jades, which are primarily composed of chromian jadeite and kosmochlor. Using a 10× loupe, we examined green jadeite samples containing black dots to confirm the presence of chromite. In this study, four Myanmar jadeite jades containing black chromites were finally selected as samples (Figure 2). All the samples were polished rock thin sections of approximately 0.03 mm (F1-1 and F1-2 are two mineral thin sections made from different locations of sample F1; J1-1 and J1-2 are two mineral thin sections made from different locations of sample J1) for microstructural observation, electron probe microanalysis (EPMA) testing, micro-X-ray fluorescence spectrometer (micro-XRF) mapping, and backscattered electron (BSE) imaging.

2.2. Methods

An Olympus polarizing microscope BX51/DP71 (Olympus Corporation, Tokyo, Japan), housed at the School of Gemology, China University of Geosciences (Beijing), was used to observe the mineral microstructure, distribution, and combination form in each section. Representative photomicrographs were obtained under reflected, plane, and cross-polarized light.
Micro-XRF (micro-area X-ray fluorescence spectroscopy) scanning enables the analysis and testing of elemental distributions in samples ranging from tens of microns to tens of centimeters. This technique offers several advantages, including in situ nondestructive analysis, rapid data acquisition, and the ability to scan large areas. In this study, in situ high-resolution multielement signal intensity data were obtained to characterize the elemental abundances in chromite-bearing samples via microarea multielement X-ray fluorescence (XRF) mapping. A Bruker XRF M4 TORNADO (Bruker Corporation, Karlsruhe, Germany), was employed to analyze the plane distributions of elements in prepared, well-polished thin mineral sections. The instrument utilized a dual silicon drift detector (SDD), a rhodium target, and a vacuum environment and was operated at a voltage of 20 kV and a current of 300 μA, with a pixel step size of 15 μm.
The chemical composition and backscattered electron (BSE) images of the samples were obtained by electron probe microanalysis (EPMA) using a JEOL JXA-8100 instrument (JEOL Corporation, Tokyo, Japan). The samples were subjected to analysis in two distinct laboratories as follows: (1) the Key Laboratory of Orogenic Belts and Crustal Evolution at Peking University in Beijing, China, under conditions of 15 kV, 10 nA, and 1 μm beam spot; (2) the State Key Laboratory of Continental Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, China, under conditions of 15 kV, 20 nA, and 3 μm beam spot. Natural and artificial minerals were employed as reference minerals. Additionally, backscattered electron (BSE) images were acquired to illustrate the spatial distributions of various minerals.

3. Results

3.1. Petrographic Observation

Microscopic observations reveal that black chromite is granular and frequently exhibits reticulate cracks within its internal structure (Figure 3). The chromite is replaced by kosmochlor and chromian jadeite. Under plane-polarized light, the black chromite edges are circumscribed by bright green kosmochlor, forming a green reactive edge around the chromite (Figure 3a). When reflective light is employed, the chromites exhibit bright white reflections, whereas the surrounding clinopyroxenes display dull gray reflections (Figure 3b). Furthermore, chromite is observed to form a relict texture (Figure 3c). A ring of light green chromian jadeite is typically observed surrounding the edges of the kosmochlor, resulting in a three-layer ring structure of relict chromite, kosmochlor, and chromian jadeite (Figure 3a). In instances where chromite is completely replaced, a two-layer ring structure of kosmochlor and chromian jadeite is formed (Figure 3d,e).
The kosmochlor frequently exhibits elongated prismatic forms, arranged in parallel arrays with particle lengths reaching ~200–300 μm. These particles display a radial growth orientation centered on the chromite. Chromian jadeite presents refined grains with particle sizes of approximately 10 μm. In general, kosmochlor in jadeite jade is typically observed in three distinct forms: (1) as a ring surrounding the core of relict chromite (Figure 3a), (2) as a reticulation within chromite (Figure 3c), and (3) as a complete replacement of chromite (Figure 3d,e).
Additionally, late-filled light green chromian omphacite veins are common in the studied samples, traversing chromite, kosmochlor, and the primary jadeite phase. The maximum width of the veins is approximately 200 μm, whereas the minimum width is less than 10 μm. The mineral grains within the veins are characterized by a fine and uniform size in microns. Omphacite delicate veins exhibit a light green hue that is markedly lighter than the brilliant green hue of kosmochlor and comparable to the green hue of chromian jadeite (Figure 3d–f).

3.2. Micro-XRF Mapping

In micro-XRF mapping analysis, the strength of the signal and brightness of the image are directly proportional to the elemental concentrations present in the sample. Chromite is present in the studied jadeite samples as particles of varying sizes (Figure 4). As illustrated in the elemental distribution map, the regions exhibiting the highest enrichment of Cr (Figure 4b) and Fe (Figure 4d) are identified as relict chromite particles. Furthermore, chromite is also characterized by a high concentration of Mn (Figure 4c). A decrease in the contents of all three elements was observed from the center of the chromite to the periphery (Figure 5). Compared with those in the matrix white jadeite, the peripheral regions of chromite in both kosmochlor and chromian jadeite also present elevated concentrations of Cr and Mn (Figure 5). In sample F1-1, the sole remaining fragment of green kosmochlor (devoid of chromite) also presented elevated Cr and Mn concentrations (Figure 5c,d). The three elements exhibit simultaneous fading and diffusion from the center to the periphery, yet a clear compositional boundary typically delineates the boundaries between the chromite, kosmochlor, and jadeite areas. Moreover, pale green Cr-omphacite veins that traverse chromite, kosmochlor, and white jadeite matrix (Figure 5f,g) have been observed to contain elevated concentrations of Cr, Mn, and Fe relative to the white jadeite matrix (Figure 5f–j).

3.3. Mineral Compositions

The mineral chemical composition data obtained from EPMA demonstrated that the chromites in this study are distinguished by relatively high concentrations of chromium and manganese, accompanied by relatively low levels of magnesium and aluminum. The chromites contain 46.18–67.11 wt.% Cr2O3 and 19.39–35.46 wt.% TFeO, and the Al2O3 content ranges from 0.17 to 10.31 wt.%, whereas the MnO content varies between 1.68 and 9.13 wt.%. The chemical compositions of chromite in jadeite jade from the present study are presented in Table S1. This table shows that chromite enrichment of manganese in jadeite jade is relatively common. The chromites in jadeite exhibit high Cr# (atomic Cr/[Cr + Al] × 100) (76–100) and low Mg# (atomic Mg/[Mg + Fe2+] × 100) (6–13) values as well as low TiO2 contents, mostly ≤0.20 wt.%. In the triangular diagram of the trivalent cation (Al-Cr-Fe3+) relations, these chromites are situated within the category of high-Cr chromite (Figure 6).
The chemical compositions of the kosmochlors are shown in Table S2. The chemical compositions of the jadeites and omphacites are shown in Table S3. Compared with other chromian pyroxenes, kosmochlor has a markedly disparate chemical composition (Table S2; see also [8,11,13,28,29]). Kosmochlor contains 17.17–30.83 wt.% Cr2O3, 0.43–2.10 wt.% TFeO, and 0.04–0.51 wt.% MnO. Chromian jadeite contains 1.07–13.31 wt.% Cr2O3, 0.50–3.00 wt.% TFeO, and 0–0.08 wt.% MnO. The kosmochlor in jadeite jade is the purest form of kosmochlor derived from terrestrial rocks, with a composition of up to 97 mol% NaCrSi2O6 [8,9,13]. The highest composition of kosmochlor in this study is 92 mol% NaCrSi2O6. The light green omphacite veins that crosscut chromite, kosmochlor, and matrix white jadeite also contain elevated levels of chromium and manganese, with 9.05 wt.% Cr2O3 and 0.42 wt.% MnO, respectively (F1-1-11). The green jadeite measured in this study contain 0.13–0.17 wt.% Cr2O3 and 0.02–0.04 wt.% MnO (F1-1-5-1 and F1-1-120). The mineral composition of the white jadeite matrix closely matches the theoretical value, and no Cr2O3 or MnO content was detected (F1-1-5-2).

4. Discussion

4.1. Characteristics of Manganese-Rich Chromite, a Supplier of Color-Causing Elements in Jadeitite

The triangular cation relationship diagram shows that chromites in jadeitite are significantly high in Cr, Fe2+, and Mn (Figure 6). Chromite is the most prevalent Cr spinel. Minerals belonging to the spinel group are composed of the AB2O4 type. The Group A ions include Mg2+, Mn2+, Fe2+, Ni2+, Zn2+, and Fe3+. The Group B ions include Al3+, Cr3+, Fe3+, and Mn3+ in addition to Mg2+, Mn2+, Fe2+, Co2+, and Ni2+, etc. Isomorphic substitution between Group A and B ions is a highly complex and common phenomenon, resulting in a series of solid solutions within the spinel group [30,31]. In a Cr spinel, the B-site is occupied by Cr3+. The unit cell of chromite contains eight Group A divalent cations, which are tetracoordinated and occupy tetrahedral positions, primarily Fe2+ and Mg. Additionally, there are 16 Group B trivalent cations, which are hexa-coordinated and occupy octahedral positions, mainly Cr, Al, and Fe3+. Furthermore, the entire chromite structure can be conceptualized as a [AO4] tetrahedron interconnected with [BO6] octahedra [30,31].
In general, chromite produced in serpentinite is characterized by high concentrations of Al and Mg, with trace amounts of Mn. The relict chromites in jadeite jades have lower Al2O3 (0.17–10.31 wt.%) and MgO (0.90–1.81 wt.%) contents than chromite in the serpentinized peridotite of Myitkyina adjacent to jadeite (Al2O3 13.69–42.83 wt.%, MgO 10.31–16.59 wt.%, Cr2O3 25.24–54.26 wt.%, MnO 0.11–0.23 wt.%) [25]. Furthermore, the relict chromites in jadeite jades exhibit relatively high Cr2O3 (46.18–67.11 wt.%) and MnO contents, with MnO contents exceeding 1.68 wt.% and reaching as high as 9.13 wt.%. These values are considerably higher than those of common chromite. The content distributions were determined via box plot analyses of chromite in jadeite jade and Myitkyina peridotites (Figure 7).
Barnes (2000) reported a greater concentration of Mn in spinel in regions where metamorphic fluids were active [32]. The elevated Mn content of Mg-Cr spinel in certain serpentinized chromite deposits indicates the potential for solid solution formation between the two phases. This hypothesis has been substantiated by experimental petrological investigations, wherein Mn2+ occupies a tetrahedral position within the spinel structure [31,33,34].
Chromite is a relic of protolithic peridotite from the subduction channel–mantle wedge and occurs in the peridotite, serpentinite, amphibolite, and jadeitite (usually kosmochlor–jadeitite) of the jadeite deposit in Myanmar [8,12,24]. The high Mn content in chromite is related to low-grade metamorphism and serpentinization [35,36,37] Mn-rich chromite was likely supplied by peridotite during and after severe serpentinization and subduction of the ophiolite [36]. Pre-existing studies of Myanmar jadeite and related rocks have shown that the process of serpentinization of the protoliths occurred before the formation of jadeite in the Myanmar jadeite mining area [12,24,38].
Serpentinite originates from a depleted mantle peridotite [39]. Tectonic stresses in the forearc mantle wedge, which was formed during the oceanic subduction process, led to the formation of serpentinite cracks. The Na-Al-Si-rich fluid precipitates in serpentinite cracks, forming the P-type (precipitation type) jadeitite [12,24,39]. P-type jadeite is nearly always white and has a composition that is nearly identical to the theoretical value. Amphibolite blackwall, the spatial and chemical intermediate between jadeitite and serpentinite, formed through metasomatic reactions as the fluid infiltrated the boundary of the serpentinite cracks [24,38]. Metamorphic reactions between Na-Al-Si-rich fluids in subduction zones and chromite-rich amphibolites (or serpentinites) lead to the formation of green jadeitite, an R-type (replacement type) jadeitite [40] (see Section 4.2 for details). The primary metamorphism of chromite caused by serpentinization was completed before the formation of jadeite.
Micro-XRF elemental distribution mapping (Figure 4) and electron probe microanalysis (EPMA) (Table S1) indicate that manganese-rich chromite is highly prevalent in jadeite jade. Although high manganese chromite is altered chromite, it existed before the formation of jadeitite. Therefore, Mn-rich chromite, which is an intermediate host of Mn, can be regarded as the supplier of color-causing elements in jadeitite.

4.2. Transfer and Diffusion of Chromium and Manganese During Metasomatic Replacement

The preservation of relict chromite in jadeite indicates its origin in metasomatic peridotite protoliths [9,11,41]. When the Na-Al-Si-rich fluid in the subduction zone underwent a metamorphic reaction with the chromite-rich protolith, kosmochlor (Cr2O3 content 17.17–30.83 wt.%) formed around the chromite (Cr2O3 content 46.18–67.11 wt.%). The edges of chromite and fractures within the chromite represent the initial sites of metamorphic diffusion, resulting in the formation of slender prisms or fine-grained outer rings of kosmochlor aggregates near the chromite. Subsequently, chromium diffused and migrated to the outer layers, replacing some of the Al3+ with Cr3+ and forming chromian jadeite (Cr2O3 content of 1.07–13.31 wt.%). The boundaries between these three mineral zones were typically clear. They formed a zonal texture (chromite–kosmochlor–chromian jadeite), and the chromium concentration decreased from the center to the periphery (Figure 8).
During this reaction, there was also a general decrease in the manganese concentration from the center to the periphery (Figure 8). The MnO content of chromite ranged from 1.68 to 9.13 wt.%, that of kosmochlor ranged from 0.04 to 0.51 wt.%, and that of chromian jadeite ranged from 0.01 to 0.09 wt.%. The white jadeite matrix contained no Cr2O3 or MnO (F1-1-5-2). In terms of spatial distribution, the Cr2O3 and MnO contents decreased with the increase in distance from chromite. Chromium and manganese are transferred and diffused in kosmochlor, as well as chromian jadeite, through a series of metamorphic reactions.
In addition, it is not uncommon to find late-filled light green omphacite veins in jadeite jade, which concurrently pass through chromite, kosmochlor, and matrix jadeite. The omphacite vein is distinguished by its green hue, which contrasts with the white matrix jadeite. It also has elevated Cr and Mn concentrations (9.05 wt.% Cr2O3 and 0.42 wt.% MnO). As it approaches the chromite center, the green color intensifies, accompanied by increases in the Cr and Mn levels (Figure 3d–f and Figure 5f–j). In addition to chemical diffusion, the penetration of fractures by late fluids facilitates the physical transport of Cr and Mn into jadeite. The multiperiod jadeite-forming fluid and late geologic modification resulted in a more homogeneous distribution of Cr and Mn in jadeite jade.

4.3. Changes in Mn from Chromite to Clinopyroxene

Mn2+ replaces Fe2+ to occupy the tetrahedral position of [MnO4] for tetra coordination in the crystal structure of chromite [33,34]. The ionic radius of the tetracoordinate Fe2+ ion is 0.063 nm. In comparison, the tetracoordinate Mn2+ ion has an ionic radius of 0.066 nm, which is close enough to easily allow for Mn2+ replacement of Fe2+. The presence of this replacement is also evidenced by the negative correlation between MnO and FeO in the chromite EPMA data (Figure 9a).
The situation is distinct when Cr and Mn enter from chromite to clinopyroxenes (e.g., kosmochlor and chromian jadeite).
Clinopyroxene is a silicate with a single-chain silicon-oxygen backbone structure, and its chemical composition can be expressed by the general formula XY[Si2O6]. In this context, X represents the M2 site. The following elements are present: Ca, Mg, Fe2+, Mn, Na and Li. Additionally, Y is present at the M1 site. The following elements are present: Mg, Fe2+, Mn, Al, Fe3+, Cr3+, and V3+ [42,43].
If the M2 sites are predominantly sodium and the M1 sites are primarily aluminum, the resulting mineral is jadeite, NaAl[Si2O6]. When the M1 sites are predominantly Cr3+, the resulting mineral is known as kosmochlor, with the chemical formula NaCr[Si2O6]. The crystal structure comprises two distinct constituent units: tetrahedral and octahedral. The tetrahedra are composed of [SiO4], while the octahedra are composed of [NaO6] and [AlO6] (in jadeite) or [CrO6] (in kosmochlor). The tetrahedra of [SiO4] represent the fundamental building blocks of silicate minerals and are arranged in chains. The octahedra of [AlO6] or [CrO6] are edge-shared [42,43].
Transition metal ions, such as Cr3+, Mn2+/3+, and Ti3+/4+, substitute for Al3+ within the [AlO6] octahedra, acting as chromophores in jadeite [5,7,18,19,44]. In the six-coordinate octahedra, the ionic radii of Cr3+, Mn3+, Mn2+, and Al3+ are 0.0615 nm, 0.0645 nm (HS), 0.083 nm (HS), and 0.0535 nm, respectively (Table 1) [18]. The Cr2O3 contents are negatively correlated with the Al2O3 contents in kosmochlor and chromian jadeite (Figure 9b,c), indicating that Cr3+ and Al3+ occupy the same octahedral position in the crystal M1 sites, mainly [CrO6] octahedra in kosmochlor and [AlO6] octahedra in jadeite. The MnO content is insufficient to discern a definitive correlation (Figure 9b,c). Given their close ionic radii, Cr3+ and Al3+ at this position can form a complete isomorphous series. The entry of fluids rich in Na, Al, and Si results in the formation of [AlO6] octahedra, which subsequently transform kosmochlor into jadeite. The green hue of jadeite is a consequence of its high Cr3+ content. For Mn3+ and Mn2+, the ionic radii of Mn3+, Cr3+, and Al3+ in the six-coordinate octahedra are relatively close. In isomorphism substitution, the closer the ionic radii are, the easier it is for each to replace the other. This suggests that Mn3+ is more likely to replace Cr3+ or Al3+ in the octahedra of the kosmochlor and jadeite crystal M1 sites in the crystal structure.
During the process of mineral crystallization, transition metal ions with a high octahedral site preference energy (OSPE) demonstrate a preferential tendency to enter the mineral lattice. The OSPEs of Cr3+ and Mn3+ are 37.7 and 17.0 kcal/mol, respectively [45,46]. Consequently, Cr3+ preferentially occupies the octahedral site of the clinopyxene structure and diffuses at a faster rate than Mn3+.

4.4. Effects of Cr and Mn on the Color of Jadeite: Comparison of Data from the Literature

It has been demonstrated that the replacement of Al3+ by Cr3+ at the M1 position in clinopyroxene is responsible for the green color of jadeite. Furthermore, the intensity of the green color increases with the increase in the concentration of Cr3+ [5,7,8,11,12]. Compared with white jadeite, lavender jadeite has a greater Mn content, predominantly in the Mn3+ form (as determined by EPR) [21]. The intensity of the color is correlated with the Mn3+ concentration [19,20,21,22,23].
The data regarding the trace elements present in the green, purple, and white jadeite jades, as measured by EPMA and LA-ICP-MS by this study and previous authors, are presented in Table 2.
In this study, the intense green kosmochlor contained 17.17–30.83 wt.% Cr2O3 and 0.04–0.51 wt.% MnO, while the peripheral green chromian jadeite contained 1.07–13.31 wt.% Cr2O3 and 0.01–0.09 wt.% MnO. Jadeite can exhibit a lavender hue at this manganese concentration, yet it retains its green appearance in kosmochlor and chromian jadeite. This finding is also consistent with data from previous studies indicating that green jadeite often has a high Cr content (500–1650 ppmw) and high Mn content (100–400 ppmw), while lavender has a high Mn content (125–991 ppmw) but minimal or no Cr (0–4 ppmw) [5,19,20,21,47,48]. Cr3+ is at least two orders of magnitude more effective in producing green coloration than Mn3+ for lavender of similar saturation [19]. Consequently, the green color is more readily visible than lavender [19]. The colorogenic effects of Mn3+ are obscured when a specific quantity of Cr3+ is present [19]. It can be postulated that lavender in jadeite manifests exclusively when a considerable concentration of manganese (approximately 100–1000 ppmw) is present and when a more effective chromophore, chromium (no Cr or within a dozen ppmw), is absent.
Table 2. The trace element concentrations of green, purple, and white jadeite jade in ppmw.
Table 2. The trace element concentrations of green, purple, and white jadeite jade in ppmw.
Color55Mn53Cr57Fe47TiSources
green *400130022,5000This study (F1-1-5-1)
green *210165032,44040This study (F1-1-120)
green (avg) **1116894222114Lu, 2012 [19]
green *100–300500–15002300–80000–500Zhang, 2008 [48]
lavender (Myanmar) **26902100Lu, 2012 [19]
lavender (Myanmar)125–9912.71–3.95298–28752.23–14.7Li, 2012 [47]
lavender (avg)1260.4534676Han et al., 2020 [21]
lavender (Myanmar)336–3722–41929–285416–56Wu et al., 2019 [20]
bluish (Japan) **27027951388Lu, 2012 [19]
bluish (Guatemala) **2.70201843Lu, 2012 [19]
blue-violet (Myanmar)26.6–1892.98–3.061255–1601469–1056Li, 2012 [47]
blue-violet (avg)150.71176688Han et al., 2020 [21]
blue-violet (Myanmar)30–695–111262–13752747–2910Wu et al., 2019 [20]
white (Myanmar)15.6–17.22.83–3.33144–2213.80–6.92Li, 2012 [47]
white (Myanmar)48–643–31955–1571206–650Wu et al., 2019 [20]
* is wt% converted to ppmw; ** is ppma converted to ppmw.
It can be concluded that during the formation of jadeite in the subduction zone, a Na-Al-Si-rich metasomatic fluid replaced the jadeite protolith (peridotite–serpentinite) bearing Mn-rich chromite. Additionally, a substantial amount of chromium (46.18–67.11 wt.%) and a considerable quantity of manganese (1.68–9.13 wt.%) in chromite are incorporated into kosmochlor (Cr2O3 content 17.17–30.83 wt.%, MnO content 0.04–0.51 wt.%), which is produced by metasomatism. As the reaction continued, the intense green kosmochlor transformed into green chromian jadeite (Cr2O3 content of 1.07–13.31 wt.%, MnO content of 0.01–0.09 wt.%). As the replacement process persists, the elements continue to diffuse. Once the chromium in the jadeite has been depleted and the manganese remains at approximately 100–1000 ppmw, the jadeite displays a lavender hue. The chromium and manganese in clinopyroxene diffuse and gradually fade during the metasomatic replacement process.
Other sources of Mn may exist. Jadeite-forming materials have been found to incorporate marine sediments enriched in Mn [24,49,50,51]. Although Mn-rich chromite may act as an intermediate host for Mn, evidence from both petrographic and chemical analyses indicates that it is a provider of chromogenic elements of the green and lavender jadeite jade. This may be a previously overlooked source of the chromogenic element (Mn) in lavender jadeite jade.

4.5. The “Spring Color with Green” Variety Further Supports the Conclusion

“Spring color with green” jadeite jade, that is, jadeite jade with both lavender and green colors (Figure 10). This particular variety of jadeite jade has been documented in Myanmar, Japan, and Guatemala. Unlike gray-green or blue-green jadeite jade affected by iron, the green color in “Spring Color with Green” jadeite jade is always bright, which is a characteristic of chromium-induced green, whereas its lavender color is characteristic of manganese-induced color. The “spring color with green” in jadeite provides visual evidence that chromium and manganese, the chromogenic elements in jadeite, often accompany each other and diffuse together.

5. Conclusions

The relict chromites identified in jadeite jades present higher Cr2O3 (46.18–67.11 wt.%) and MnO (1.68–9.13 wt.%) contents and lower Al2O3 (0.17–10.31 wt.%) and MgO (0.90–1.81 wt.%) contents than the chromite present in the serpentinized peridotite of Myitkyina, which is situated in proximity to jadeite deposits. This manganese-rich chromite may act as an intermediate host for Mn, but evidence from both petrographic and chemical analyses indicates that it is a provider of chromogenic elements of the green (Cr) and lavender (Mn) jadeite jade. The chemical diffusion of chromium and manganese occurs in the following metamorphic pathway: Mn-rich chromite → kosmochlor → chromian jadeite → jadeite.
The Ca- and Mg-rich fluids subsequently traversed microfractures through Mn-rich chromite, kosmochlor, and chromian jadeite, ultimately forming Cr-rich omphacite veins. This process facilitated the physical diffusion of Cr and Mn, enabling their more extensive and uniform distribution.
The chromium pyroxene (kosmochlor, chromian jadeite, and chromian omphacite) in proximity to chromite also presented a high manganese content. The presence of Cr3+ is responsible for the green coloration observed in jadeite, whereas Mn3+ is responsible for the lavender coloration. The chromophore effectiveness of Cr is greater than that of Mn. The emergence of the lavender hue in jadeite is contingent upon the presence of a relatively high concentration of manganese (approximately 100–1000 ppmw) and the simultaneous absence of a more effective chromophore, chromium (no Cr or up to a dozen ppmw).

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cryst15080704/s1, Table S1: Chemical compositions of chromites in jadeite jade; Table S2: Chemical compositions of kosmochlors in jadeite jade; Table S3: Chemical compositions of jadeites and omphacites in jadeite jade.

Author Contributions

Methodology, Y.Z. and G.S.; Software, Y.Z. and J.W.; Formal analysis, Y.Z.; Investigation, Y.Z. and J.W.; Resources, G.S.; Data curation, Y.Z.; Writing—original draft, Y.Z.; Writing—review & editing, Y.Z. and G.S.; Visualization, J.W.; Supervision, G.S.; Project administration, G.S.; Funding acquisition, Y.Z. and G.S. All authors have read and agreed to the published version of the manuscript.

Funding

This investigation was supported by the National Natural Science Foundation of China (grant number 42273044) and 2025 Teaching Reform—Research and Application of Teaching Laboratory and Experimental Technology (No. 640125002, Project SYJS202504).

Data Availability Statement

The data presented in this study are available within the article and the Supporting Information (including Tables S1–S3).

Acknowledgments

The authors thank Ye Yuan and Bijie Peng for the technical support of the lab (School of Gemology, China University of Geosciences, Beijing).

Conflicts of Interest

The authors declare no conflicts of interest.

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Crystals 15 00704 g001
Figure 1. Photographs of Feicui (jadeite jade): (a) “imperial” green, (b) lavender, and (c) blue-violet.
Figure 1. Photographs of Feicui (jadeite jade): (a) “imperial” green, (b) lavender, and (c) blue-violet.
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Figure 2. Photos of the studied Myanmar Feicui (jadeite jade) containing residual chromite.
Figure 2. Photos of the studied Myanmar Feicui (jadeite jade) containing residual chromite.
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Figure 3. Microphotographs (plane-polarized light: (a,c–e); reflective light: (b)) and BSE image (f) showing textures and mineral assemblages in study sample F1-1. Chr = chromite; Kos = kosmochlor; Omp = omphacite; Cr-Omp = Cr-omphacite; Jd = jadeite.
Figure 3. Microphotographs (plane-polarized light: (a,c–e); reflective light: (b)) and BSE image (f) showing textures and mineral assemblages in study sample F1-1. Chr = chromite; Kos = kosmochlor; Omp = omphacite; Cr-Omp = Cr-omphacite; Jd = jadeite.
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Figure 4. Elemental mapping of samples F1-1 and F1-2 via micro-XRF revealed that chromite is rich in Cr, Mn, and Fe. (a) Photo of the rock thin section. The yellow dotted line shows the boundary between the green and white jadeite. (b–d) Elemental distribution maps of Cr, Mn, and Fe, respectively. Chr = chromite; W-Jd = white jadeite.
Figure 4. Elemental mapping of samples F1-1 and F1-2 via micro-XRF revealed that chromite is rich in Cr, Mn, and Fe. (a) Photo of the rock thin section. The yellow dotted line shows the boundary between the green and white jadeite. (b–d) Elemental distribution maps of Cr, Mn, and Fe, respectively. Chr = chromite; W-Jd = white jadeite.
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Crystals 15 00704 g005
Figure 5. Micrographs (cross-polarized light: (a,g); plane-polarized light: (b,f)) and micro-XRF maps (c–e,h–j) show the structural characteristics of chromite that has been replaced by kosmochlor in samples F1-1 (note the outward decrease in the concentrations of Mn, Cr, and Fe in this ring structure) and that the pale green Cr-omphacite veins (f,g) contain elevated concentrations of Cr (h), Mn (i), and Fe (j) relative to the white jadeite matrix. Chr = chromite; Kos = kosmochlor; Cr-Omp = Cr-omphacite; W-Jd = white jadeite.
Figure 5. Micrographs (cross-polarized light: (a,g); plane-polarized light: (b,f)) and micro-XRF maps (c–e,h–j) show the structural characteristics of chromite that has been replaced by kosmochlor in samples F1-1 (note the outward decrease in the concentrations of Mn, Cr, and Fe in this ring structure) and that the pale green Cr-omphacite veins (f,g) contain elevated concentrations of Cr (h), Mn (i), and Fe (j) relative to the white jadeite matrix. Chr = chromite; Kos = kosmochlor; Cr-Omp = Cr-omphacite; W-Jd = white jadeite.
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Figure 6. (a) Trivalent (Al-Cr-Fe3+) and (b) divalent (Mg-Fe2+-Mn) cation relations of relict chromites in jadeite jade and of chromites from the adjacent Myitkyina peridotite [11,25,26,27].
Figure 6. (a) Trivalent (Al-Cr-Fe3+) and (b) divalent (Mg-Fe2+-Mn) cation relations of relict chromites in jadeite jade and of chromites from the adjacent Myitkyina peridotite [11,25,26,27].
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Figure 7. The box plot of content distributions for chromite in jadeite jade and Myitkyina peridotites.
Figure 7. The box plot of content distributions for chromite in jadeite jade and Myitkyina peridotites.
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Figure 8. A general decreasing trend in the Cr2O3 and MnO contents from the central chromite to the peripheral kosmochlor and chromian jadeite was displayed. (a) Microscope photographs under cross-polarized light and compositional content scatter plots of samples F1-2; (b–d) backscattered electron (BSE) images and compositional content scatter plots of samples J1-1, J2, and J3, respectively. The numbers in the figures of left column represent the sampling spots, which correspond to the x-axes in the scatter plots of right column, and their chemical compositions are shown in Tables S1–S3. Chr = chromite, Kos = kosmochlor, and Cr-Jd = Cr-jadeite.
Figure 8. A general decreasing trend in the Cr2O3 and MnO contents from the central chromite to the peripheral kosmochlor and chromian jadeite was displayed. (a) Microscope photographs under cross-polarized light and compositional content scatter plots of samples F1-2; (b–d) backscattered electron (BSE) images and compositional content scatter plots of samples J1-1, J2, and J3, respectively. The numbers in the figures of left column represent the sampling spots, which correspond to the x-axes in the scatter plots of right column, and their chemical compositions are shown in Tables S1–S3. Chr = chromite, Kos = kosmochlor, and Cr-Jd = Cr-jadeite.
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Figure 9. Compositional correlation plots for (a) chromite, (b) kosmochlor and (c) chromian jadeite. The x-axes represent the sampling spots.
Figure 9. Compositional correlation plots for (a) chromite, (b) kosmochlor and (c) chromian jadeite. The x-axes represent the sampling spots.
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Figure 10. Photo of a pair of “spring color with green” jadeite jade bracelets.
Figure 10. Photo of a pair of “spring color with green” jadeite jade bracelets.
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Table 1. The radii of the ions.
Table 1. The radii of the ions.
CNIonIonic Radius (nm)Spin State
4Si4+0.026
Fe2+0.063
Mg2+0.057
Mn2+0.066
Al3+0.039
Fe3+0.049
8Na+0.118
6Al3+0.054
Cr3+0.062
Fe2+0.078HS
Fe3+0.0645HS
Mn3+0.0645HS
Mn2+0.083HS
CN = coordination number; HS = high spin.
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Zhang, Y.; Shi, G.; Wen, J. Manganese-Rich Chromite in Myanmar Jadeite Jade: A Critical Source of Chromium and Manganese and Its Role in Coloration. Crystals 2025, 15, 704. https://doi.org/10.3390/cryst15080704

AMA Style

Zhang Y, Shi G, Wen J. Manganese-Rich Chromite in Myanmar Jadeite Jade: A Critical Source of Chromium and Manganese and Its Role in Coloration. Crystals. 2025; 15(8):704. https://doi.org/10.3390/cryst15080704

Chicago/Turabian Style

Zhang, Yu, Guanghai Shi, and Jiabao Wen. 2025. "Manganese-Rich Chromite in Myanmar Jadeite Jade: A Critical Source of Chromium and Manganese and Its Role in Coloration" Crystals 15, no. 8: 704. https://doi.org/10.3390/cryst15080704

APA Style

Zhang, Y., Shi, G., & Wen, J. (2025). Manganese-Rich Chromite in Myanmar Jadeite Jade: A Critical Source of Chromium and Manganese and Its Role in Coloration. Crystals, 15(8), 704. https://doi.org/10.3390/cryst15080704

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