New Insights into Chromogenic Mechanism and the Genesis of Blue Jadeite from Guatemala

Abstract

While existing studies on Guatemalan jadeite have predominantly focused on green varieties, the coloration mechanisms and origin of its blue counterparts remain poorly understood. Therefore, the present study provides the first comprehensive investigation of the Guatemalan blue jadeite using an integrated analytical approach, which combines Raman spectroscopy, micro X-ray fluorescence (µ-XRF), electron microprobe analysis (EMPA), X-ray diffraction (XRD), UV-Vis spectroscopy, and Cathodoluminescence (CL) imaging on seven representative samples. The results demonstrate that these jadeites consist of two distinct phases: a primary jadeite phase (NaAlSi₂O₆) and a secondary omphacite that form by metasomatic alteration by Mg-Ca-Fe-rich fluids. Spectroscopic analysis reveals that the blue coloration is primarily controlled by Fe³⁺ electronic transitions (with characteristic absorption at 381 nm and 437 nm) coupled with Fe²⁺-Ti⁴⁺ intervalence charge transfer, supported by μ-XRF mapping showing strong Fe-Ti spatial correlation with color intensity. CL imaging documents a multi-stage formation history involving initial high-pressure crystallization (Jd-I) followed by fluid-assisted recrystallization forming Jd-II and omphacite. The detection of CH₄, CO and H₂O in the fluid inclusions by Raman spectroscopy indicates formation in a serpentinization-related reducing environment, while distinct CL zoning patterns confirm a fluid-directed crystallization (P-type) origin. These findings not only clarify the chromogenic processes and petrogenesis of Guatemalan blue jadeite but also establish key diagnostic criteria for its identification, advancing our understanding of fluid-derived jadeite formation in subduction zone environments.

1. Introduction

Jadeite is a high-pressure metamorphic pyroxene mineral (NaAlSi₂O₆) of considerable economic and cultural importance. Its formation typically occurs under high-pressure, low-temperature (HP-LT) conditions (1.5–3.0 GPa, 200–500 °C) at the oceanic plate–mantle wedge interface [1], primarily through either direct precipitation from fluids or fluid-mediated metasomatic processes [2]. Globally, jadeite displays a diverse color spectrum ranging from white to various chromatic varieties, including intense green [3], bluish-green [4], blue [5], violet (commonly referred to as ‘lavender’) [6], yellow, gray, and black. While extensive research has been conducted on green jadeite, encompassing investigations into its coloration mechanisms [7], provenance determination [8], and geological origin analysis [9], comparable systematic studies on blue varieties are notably lacking [10].

Blue jadeites of significant value are found in numerous locations around the world, with Myanmar recognized as the premier source, followed by Guatemala [11]. Notable occurrences extend to the Sorkhan region in southeastern Iran and Japan’s Ohmi-Kotaki area [12], with blue jadeites from these localities exhibiting significant divergence in coloration mechanisms, elemental compositions (both major and trace), and genetic origins. The Hpakant mine (Myanmar) yields blue jadeite colored predominantly through Fe²⁺-Fe³⁺ charge transfer [13], typically containing <0.01 wt.% titanium. In contrast, Ohmi-Kotaki specimens demonstrate intimate paragenesis with albite and analcime [14], while Itogawa blue jadeite derives its hue from titanium impurities (TiO₂ ≤ 6 wt.%), likely via Ti-Fe intervalence charge transfer [15,16]. Current research on Guatemalan blue jadeite remains limited: since Harlow et al.’s 2004 identification of a new “Olmec blue” source—texturally and chromatically analogous to turquoise used by the Olmec civilization [5,11,14]—only chromogenic studies of Guatemalan “blue water” jadeite [4] and spectral comparisons with Myanmar counterparts [17,18] exist. Consequently, the color development mechanisms and origin determination criteria for Guatemalan blue jadeite require substantive further investigation.

This study presents a novel suite of representative Guatemalan jadeite samples exhibiting a blue-to-green chromatic continuum, designated as Opa.B, Bla.B, Gra.B, Maz.B, Mot.B, Lig.B and Lak.B based on dominant color saturation. Through an integrated analytical suite encompassing Raman spectroscopy, XRD, UV-Vis spectrophotometry, µ-XRF, EPMA, and CL, we systematically investigated the chromogenic mechanisms, chemical signatures, and microstructural characteristics of these blue jadeites. Our research directly addresses the fundamental knowledge gap regarding the relationships between chromogenic factors and provenance in Guatemalan blue jadeitite, highlighting petrogenetic evidence that points to a direct crystallization genesis and promoting empirically verifiable criteria for authenticating geological origin.

2. Materials and Methods

The Guatemalan jadeite samples examined in this study exhibit a diverse color continuum spanning gray-blue, dark blue, speckled blue, light blue, lake blue, black blue, and opaque blue hues. Each sample displays characteristic surface luster, and characteristic internal features such as cotton-like inclusions and colored bands, which significantly influence its color properties (Figure 1). All analyses were conducted at specialized laboratories under standardized protocols. Phase identification via X-ray diffraction (XRD) employed a PANalytical X’Pert Pro diffractometer (Gemological Experimental Teaching Center, China University of Geosciences, Beijing, China) with Cu-Kα radiation (40 kV, 40 mA), scanning from 5° to 70° 2θ at 0.02° increments and referenced against the ICDD PDF-2 database.

Quantitative major-element chemistry was determined by electron microprobe analysis (EPMA) using a JEOL JXA-8230 instrument (Shandong Institute of Geological Sciences, Jinan, China). Natural mineral standards (jadeite for Na/Al, hematite for Fe) calibrated measurements under ZAF matrix correction, with operational parameters set at 20 kV accelerating voltage, 20 nA beam current, and 5 μm beam diameter, achieving a detection limit of 0.01 wt.% and analytical precision of ±1%–2%.

Spectroscopic characterization included Raman microspectroscopy (Horiba HR Evolution confocal system, Villeneuve d’Ascq, France. 532 nm laser excitation, 100 mW power, 1 cm⁻¹ spectral resolution, 5 μm spot size) with spectral assignments validated against RRUFF database reference R070240 (University of Arizona, Tucson, AZ, USA). UV-Vis reflectance spectrophotometry (Shimadzu UV-3600; Kyoto, Japan; BaSO₄-calibrated reflectance mode, 300–900 nm range) elucidated chromogenic mechanisms. Sample integrity was verified by polarized light microscopy (Olympus BX-51; Tokyo, Japan; 10–40× magnification) to exclude specimens with internal fractures, while gemological attributes were assessed through stereomicroscopy (Nanjing Baoguang GI-MP22, Nanjing, China) and Chelsea filter observations.

Complementary microstructural analysis integrated cathodoluminescence (CL) imaging via a Gatan MonoCL4 system (Gatan, Inc., Pleasanton, CA, USA) coupled to SEM (Thermo Fisher Scientific Phenom XL; Thermo Fisher Scientific, Eindhoven, The Netherlands; 15 kV acceleration voltage, 10 nA beam current) to resolve growth zonation, supplemented by micro-X-ray fluorescence (μ-XRF) mapping (Bruker M4 TORNADO; Billerica, USA; Rh anode, 50 kV/600 μA, 20 μm spatial resolution) calibrated against NIST SRM 610 glass (National Institute of Standards and Technology, Gaithersburg, MD, USA) for in situ elemental distribution.

3. Geological Background

The Guatemala Suture Zone (GSZ) constitutes a key tectonic boundary demarcating the convergence of the North American and Caribbean plates [19]. This composite structural domain integrates ophiolitic fragments (e.g., Juan de Paz massif), serpentinite mélanges, and metavolcanic-sedimentary sequences, tectonically interleaved with high-grade metamorphic assemblages—including the schist-gneiss-marble suites of the Chuacús and Las Ovejas complexes—along the active Motagua Fault System (MFS) (Figure 2). The North Motagua Mélange (NMM) north of the MFS contains high-pressure metabasites occurring as garnet amphibolites, garnet blueschists, retrograde clinozoisite-bearing eclogites, jadeitites, albitites, and omphacite-taramite rocks, which collectively record metamorphic gradients from greenschist-blueschist facies (200–400 °C, ≤1 GPa) to eclogite facies conditions (620 °C, ~1.7 GPa) [20,21,22,23]. Conversely, the South Motagua Mélange (SMM) preserves lawsonite eclogites, glaucophane-bearing metabasites, and jadeitites indicative of ultrahigh-pressure/low-temperature (UHP-LT) regimes (~2.6 GPa, 470 °C) [24], although epidote amphibolite blocks near La Ceiba denote localized thermal anomalies within this cold subduction system [25,26,27].

Geochronological data revealed distinct tectonic histories across the MFS. ⁴⁰Ar/³⁹Ar dating has shown that the eclogites occurring north of the fault are of younger age (77–65 Ma) than those to the south (125–116 Ma) [28]. Sm-Nd isochrons from eclogites yield ages of 144–126 Ma [22], while U-Pb zircon dating of jadeitites indicates crystallization at 98–80 Ma (north) and 158–130 Ma (south) [19,29,30,31]. These age discrepancies suggest that jadeitites on either side of the MFS formed during separate subduction events undergoing differing fluid–rock interactions [19].

The GSZ thus preserves a record of multi-stage subduction, metasomatism, and exhumation, with jadeitite formation linked to deep fluid processes in contrasting tectonic settings [32]. This duality underscores the zone’s significance in understanding subduction-related mineralogical diversity.

4. Results

4.1. Microstructure

Microscopic examination reveals distinct banding in sample Mot.B (Figure 3C). Sample Lig.B contains snowflake-like albite aggregates (Figure 3B) and interconnected microcrack networks (Figure 3C), suggesting partial albite replacement and incipient structural degradation of the jadeite. The yellow areas observed within the matrix of sample Lak.B (Figure 3D) represent secondary mineral manifestations rather than intrinsic coloration of primary jadeite. This coloration results from paragenetic oxidation processes in which iron-containing solutions percolate through jadeite’s fracture networks, intergranular boundaries, and near-surface zones via diffusion transport. Subsequent precipitation yielded goethite [FeO(OH)·nH₂O] coatings along these permeable pathways, imparting the distinctive yellow hues. These features reflect secondary mineral accumulation associated with prolonged weathering processes.

4.2. XRD Analysis

X-ray diffraction (XRD) allows for the identification of minerals based on their characteristic crystalline structure. Blue jadeite samples from Guatemala (Figure 4) can be classified into two distinct compositional phases, forming part of a solid solution: a “jadeite phase” and an “omphacite phase”. Specifically, samples with higher abundances of the jadeite endmember (typically >75–80 mol% jadeite) fall within the ‘jadeite-phase’, while samples significantly enriched in the omphacite component (characterized by a large substitution of Ca(Mg,Fe)Si₂O₆ for NaAlSi₂O₆, with jadeite contents generally between 60 and 75 mol%) are classified identified as the ‘omphacite-phase’ [33].

Seven distinct varieties of Guatemalan blue jadeite were characterized by XRD (Figure 3), and strongest peaks are observed in the samples Gra.B, Mot.B, Lig.B, and Lak.B, which correspond well to the reference peaks of the jadeite standards. In contrast, samples Opa.B and Bla.B are primarily composed of omphacite with minor jadeite content. Compared to the jadeite-rich samples, these omphacite-dominant samples exhibit characteristic peak shifts towards lower angles attributable to different crystallographic parameters.

4.3. Jadeite Phase

Raman spectroscopic analysis, the polarized light microscopic examination of structural features, combined with spectroscopic and crystallographic analyses, confirmed that the predominant mineral is jadeite. Raman spectra of the blue jadeite specimens exhibit characteristic vibrational modes at 371, 436, 528, 694, 985, and 1032 cm⁻¹ (Figure 5), which are diagnostic features of the jadeite structure. The narrow full-width at half-maximum (FWHM) values observed in these samples indicate well-ordered [SiO₄]⁴⁻ tetrahedral configurations [7], while peak broadening and shifts in samples Gra.B and Opa.B suggest lattice disorder attributable to weathering effects or reduced crystallinity.

Spectral deconvolution reveals that the 985 cm⁻¹ and 1032 cm⁻¹ bands correspond to non-bridging oxygen (Si-O⁻) stretching and symmetric Si-O stretching vibrations, respectively, whereas the 694 cm⁻¹ feature arises from symmetric bending of Si-O-Si bridges [7]. Metal-oxygen octahedral vibrations in the 200–490 cm⁻¹ region display cation-dependent signatures, with Fe-O modes (FeO = 0.10–2.18 wt.%) dominating the 225–325 cm⁻¹ range, while Mg-O vibrations (MgO = 0.00–5.31 wt.%) produce distinct peaks at 371 cm⁻¹ and 436 cm⁻¹.

CL reveals the internal growth zoning, trace element distribution, and crystal defects in minerals by detecting the light they emit under electron bombardment [34]. CL imaging (Figure 6b) of jadeite domains (Jd_90–100) exhibits striking blue-red luminescence zonation, characterized by finely oscillatory growth bands with alternating red-blue coloration. Backscattered electron (BSE) imaging (Figure 6a,c,d) effectively discriminates mineral phases based on their atomic number, where brighter regions correspond to elements with higher average atomic numbers. Backscattered Electron (BSE) imaging revealed a clear contrast in composition, which, upon quantitative analysis by Electron Probe Microanalysis (EMPA) (

Table 1. Major oxides composition of blue jadeite (Jd) in wt.% *.

Comment	Lig.B-1	Lig.B-2	Lig.B-3	Maz.B-1	Maz.B-2	Maz.B-3	Mot.B-1	Mot.B-2	Mot.B-3
SiO2	58.39	59.70	59.22	58.48	59.44	57.94	57.32	57.79	57.79
TiO2	0.21	0.27	0.16	0.04	0.00	0.06	0.15	0.07	0.11
Al2O3	22.04	23.40	25.77	25.78	25.56	25.97	20.49	25.02	21.61
Cr2O3	0.00	0.00	0.00	0.04	0.00	0.00	0.04	0.07	0.00
Fe2O3	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
FeO	1.63	1.38	0.55	0.27	0.18	0.22	1.91	0.24	2.18
MnO	0.00	0.00	0.00	0.04	0.07	0.06	0.10	0.00	0.04
MgO	2.24	1.35	0.46	0.23	0.36	0.20	2.27	0.12	1.81
CaO	2.82	1.83	0.58	0.37	0.33	0.23	3.42	0.31	2.87
Na2O	13.61	14.27	14.78	14.43	14.28	15.08	12.63	14.49	13.09
K2O	0.00	0.01	0.01	0.01	0.02	0.01	0.02	0.00	0.01
Total	100.94	102.21	101.53	99.69	100.24	99.77	98.34	98.11	99.49
End- members
Q(quartz)	10.75	7.59	2.98	1.70	1.85	0.93	14.55	1.23	12.22
Jd(jadeite)	82.90	90.45	97.02	98.30	98.15	94.94	84.39	98.76	86.01
Ae(aegirine)	6.34	1.96	0.00	0.00	0.00	4.13	1.06	0.01	1.76
Name	Jd	Jd	Jd	Jd	Jd	Jd	Jd	Jd	Jd
Comment	Lak.B-1	Lak.B-2	Lak.B-3	Opa.B-2	Opa.B-5	Opa.B-6
SiO2	57.48	58.39	58.42	57.77	59.33	58.71
TiO2	0.07	0.08	0.23	0.02	0.00	0.06
Al2O3	24.04	24.96	22.54	21.92	24.90	25.20
Cr2O3	0.00	0.00	0.03	0.00	0.00	0.01
Fe2O3	0.00	0.00	0.00	0.00	0.00	0.00
FeO	0.66	0.72	1.27	0.66	0.26	0.56
MnO	0.00	0.09	0.00	0.08	0.02	0.02
MgO	0.73	0.29	1.27	2.10	0.09	0.28
CaO	0.75	0.41	1.37	3.02	0.28	0.69
Na2O	14.36	14.52	13.64	12.29	14.84	14.61
K2O	0.01	0.00	0.00	0.03	0.02	0.00
Total	98.10	99.46	98.77	97.88	99.73	100.13
End- members
Q(quartz)	3.28	2.56	7.73	7.56	0.64	2.71
Jd(jadeite)	94.68	97.43	92.26	92.44	98.87	97.15
Ae(aegirine)	2.04	0.01	0.01	0.00	0.49	0.15
Name	Jd	Jd	Jd	Jd	Jd	Jd

* Electron microprobe data pertaining to jadeite-phase domains in the samples.

) [24], was unequivocally attributed to two distinct generations of jadeite characterized by their specific major element contents: (I) Jd-I (Jd_90–100 = Na/(Na + Ca) atomic% × 100) occurs as elongated prismatic or anhedral grains displaying pronounced compositional zoning. The dark-gray cores show markedly higher jadeite content compared to the light-gray rims, with substantial variations in CaO, MgO, and FeO concentrations. with rhythmic variations in MgO (0.12–2.27 wt.%), CaO (0.23–3.42 wt.%), and Al₂O₃ (17.20–26.27 wt.%) contents. The darker cores in BSE images correlate with Ca-rich (red luminescent) and Al-rich (blue luminescent) zones in CL [35]. (II) Jd-II (Jd_80–90) forms interstitial fillings surrounding Jd-I, with finer grain sizes indicative of recrystallization-induced grain size reduction. The formation of Jd-II is accompanied by minor omphacite development (Figure 7), where FeO (0.10–2.18 wt.%) incorporation leads to luminescence quenching, manifesting as dark blue CL emission. Projection of pyroxene end-members according to the nomenclature of Morimoto (1988) [36] confirms the classification of these minerals as jadeite, consistent with XRD and Raman spectroscopy results. Correlative BSE and CL imaging delineates compositional gradients from a mid-ocean ridge basalt (MORB) source to modified crustal components, documenting a complex evolutionary history spanning peak high-pressure metamorphism to retrograde alteration [37].

4.4. Omphacite Phase

The omphacite in the samples primarily formed through metasomatic replacement of jadeite by Mg-Ca-Fe-rich fluids [38], involving coupled cationic substitution of Na⁺ by Ca²⁺ and Al³⁺ by Mg²⁺ in the pyroxene structure. This metasomatism resulted in compositionally heterogeneous omphacite, predominantly occurring as vein-like inclusions (Figure 8) within the jadeite matrix, where it coexists with stage II jadeite (Jd-II). The replacement reaction can be expressed as follows:

$$\mathrm{J}\mathrm{a}\mathrm{d}\mathrm{e}\mathrm{i}\mathrm{t}\mathrm{e}\left(\mathrm{N}\mathrm{a}\mathrm{A}\mathrm{l}{\mathrm{S}\mathrm{i}}_2{\mathrm{O}}_6\right)+{\mathrm{C}\mathrm{a}}^{2+}+{\mathrm{M}\mathrm{g}}^{2+}\to \mathrm{O}\mathrm{m}\mathrm{p}\mathrm{h}\mathrm{a}\mathrm{c}\mathrm{i}\mathrm{t}\mathrm{e}\left(\right(\mathrm{N}\mathrm{a},\mathrm{C}\mathrm{a}\left)\right(\mathrm{A}\mathrm{l},\mathrm{M}\mathrm{g}\left){\mathrm{S}\mathrm{i}}_2{\mathrm{O}}_6\right)+{\mathrm{N}\mathrm{a}}^{+}$$

Backscattered electron (BSE) imaging of samples Gra.B, Lig.B, and Mot.B reveals (Figure 9) omphacite occurring as light-gray veinlet or island-like domains. CL(CL) microscopy shows that the light-gray BSE domains exhibit blue-black or non-luminescent responses. BSE imaging of sample Lak.B indicates (Figure 8) that infiltration of Ca-Mg-Fe-rich fluids facilitated the substitution of Na⁺ by Ca²⁺ and Al³⁺ by (Mg²⁺,Fe²⁺) [39], driving the transformation of jadeite into omphacite ((Na,Ca)(Al,Mg,Fe)Si₂O₆).

Electron microprobe analysis (EMPA) (

Table 2. Major oxides composition of blue omphacite samples (wt.%) *.

Comment	Bla.B-1	Bla.B-2	Bla.B-3	Bla.B-4	Bla.B-5	Lak.B-7	Opa.B-1	Opa.B-3	Opa.B-4
SiO2	58.27	59.01	57.07	58.17	59.11	57.14	57.92	57.99	55.66
TiO2	0.07	0.23	0.11	0.22	0.20	0.06	0.03	0.07	0.00
Al2O3	18.91	19.34	17.20	19.19	20.02	20.48	10.03	13.11	6.65
Cr2O3	0.07	0.08	0.00	0.09	0.14	0.05	0.00	0.05	0.05
Fe2O3	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
FeO	1.19	1.39	1.35	1.73	1.33	0.87	2.26	1.05	2.05
MnO	0.09	0.07	0.16	0.00	0.01	0.00	0.01	0.07	0.01
MgO	3.99	3.56	5.31	3.55	3.46	2.52	9.92	8.14	12.28
CaO	6.56	5.33	8.52	5.54	5.08	2.84	15.48	11.91	18.50
Na2O	11.37	11.95	9.83	11.33	11.98	13.59	6.42	8.01	4.14
K2O	0.01	0.00	0.00	0.01	0.01	0.00	0.01	0.00	0.00
Total	100.52	100.96	99.54	99.82	101.31	97.56	102.08	100.38	99.34
End- members
Q(quartz)	24.06	20.81	32.30	22.38	20.14	11.43	39.97	29.11	55.25
Jd(jadeite)	75.94	79.19	67.70	77.62	79.86	78.72	51.75	67.07	36.67
Ae(aegirine)	0.00	0.00	0.00	0.00	0.00	9.86	8.28	3.82	8.08
Name	Omp	Omp	Omp	Omp	Omp	Omp	Omp	Omp	Omp

* Electron microprobe data pertaining to jadeite-phase domains in the samples.

) reveals that the darker CL domains contain higher concentrations of MgO (2.1–3.8 wt.%), CaO (1.2–2.5 wt.%), and total FeO (TFeO: 4.5–6.2 wt.%) compared to the brighter luminescent zones, corresponding to lower jadeite purity (Jd_76–80). Sample Opa.B consists predominantly of omphacite, with diagnostic Raman peaks (Figure 7) at 359, 679, and 1024 cm⁻¹. Polarized light microscopy indicates that this sample exhibits a well-crystallized, fine-grained texture. Comparative Raman analysis between light-blue and dark-blue zones reveals sharper peaks and a downshifted 373 cm⁻¹ band in the former, suggesting enhanced lattice ordering, whereas peak broadening in the latter reflects incomplete crystal growth development luminescent.

5. Discussion

5.1. The Chromogenic Mechanism of Blue Jadeite

The origin of blue color in jadeite remains a subject of scientific debate. Our study utilized UV-Vis spectroscopic analysis for the preliminary identification of the chromophores responsible for the blue color in Guatemalan jadeite. UV-Vis spectroscopic analysis reveals characteristic absorption features in the blue jadeite samples (Figure 10), with an absorption band at 381 nm and a minimum at 437 nm in the blue-violet region, corresponding to electronic transitions of octahedrally coordinated Fe³⁺. The absorption spectral features exhibit significant narrowing and intensification in the light blue samples, indicating that the incorporation of Fe³⁺ [38] in the crystal lattice alters the color spectrum of jadeite. Within the crystal lattice of NaAlSi₂O6, the coupled substitution of Al³⁺ by Fe²⁺/Fe³⁺ enables charge-compensated intervalence transitions that selectively absorb red light and transmit blue wavelengths, forming the fundamental cause of coloration [16,21,39]. This mechanism is consistently supported by characteristic absorption near 792 nm, attributed to Fe²⁺, along with pervasive grayish undertones observed across samples [35]. More significantly, the widely developed cryptic oscillatory zoning—formed under prolonged and stable pressure-temperature conditions with fluctuating fluid compositions during metasomatic alteration—reflects periodic changes in the physicochemical environment. In particular, within zones where jadeite transforms into Fe-enriched omphacite, these rhythmic patterns result in pronounced microscale Fe-concentration gradients. These heterogeneities directly regulate the efficiency of Fe²⁺ → Fe³⁺ intervalence charge transfer, thereby exerting critical control over the intensity and distribution of blue color saturation [40].

Micro-X-ray fluorescence (μ-XRF) mapping revealed the two-dimensional distribution and relative concentrations of major, minor, and trace elements across the jadeite sample surface (Figure 11). These results provide direct spatial evidence supporting these spectroscopic observations, showing Fe-Ti covariance in blue-colored regions with color intensity positively correlating with elemental concentrations (reddish hues indicating higher concentrations). This spatial correlation directly links octahedral Fe³⁺ occupancy with the 437 nm absorption feature while revealing the contribution of Fe²⁺→Ti⁴⁺ intervalence charge transfer [16] to the blue coloration of Guatemalan jadeite (Figure 10).

5.2. Composition Analysis of Blue Jadeite

CL [40,41] analysis reveals two distinct mineralization stages in Guatemalan jadeite [41,42]. The early-stage Jd-I phase (Jd_94–99) exhibits high chemical purity, indicative of crystallization under high-pressure metamorphic conditions within a relatively closed system. These high-purity jadeites (Jd_90–100) display bright blue-purple CL [33,35], potentially linked to subduction-related slab dehydration (Figure 12). In contrast, the later-stage Jd-II phase (Jd_74–87) displays broader compositional variations, resulting from metasomatic alteration by Mg-Ca-Fe-rich fluids during retrograde metamorphism (350–450 °C, 0.7–1.0 GPa [23,27]). Fluid infiltration triggered dissolution-reprecipitation of the early high-purity jadeite, leading to systematic Na₂O decreases from 13.85 wt.% (Jd-I) to 9.83 wt.% (Jd-II) and significant CaO enrichment (≤15.48 wt.%), causing the CL in jadeite to exhibit a red luminescent characteristic [43]. This process enhanced Fe²⁺→Ti⁴⁺ charge transfer in edge-sharing octahedra, inducing lattice distortion and forming the key chromogenic mechanism for the characteristic blue coloration. Notably, elevated MgO content (9.92–12.28 wt.%) in the metasomatic Jd-II phase suggests the involvement of serpentinite-derived fluids. These open-system fluid–rock interactions substantially modified the primary jadeite chemistry, ultimately establishing a distinct compositional gap between jadeite and omphacite in the Jd-Aug-Ae ternary system [19].

Micro-X-ray fluorescence (μ-XRF) mapping confirms Fe-Ti co-enrichment in metasomatism omphacite domains, where CL response shows significant quenching due to Fe²⁺/Fe³⁺ d-d transitions [44]. The increased Mg²⁺ substitution not only suppresses Cr³⁺ incorporation (Cr₂O₃ < 0.05 wt.%) but also amplifies lattice strain, thereby intensifying the Fe-Ti-dominated chromophore system [21].

The jadeite phase transformation history comprehensively documents the dynamic fluid-rock interactions in subduction zones. The early high-pressure Jd-I phase (Al₂O₃ up to 26.27 wt.%) represents a relatively closed system, whereas the retrograde Jd-II + Omphacite assemblage reflects open-system, fluid-mediated metasomatism. This multistage evolution establishes significant compositional and structural contrasts between jadeite and omphacite, while precisely controlling transition metal ion speciation (Fe²⁺/Ti⁴⁺ charge transfer) to govern the gemstone’s coloration. The findings emphasize that the chemical composition (particularly Ca/Mg ratio) and redox conditions of subduction zone fluids are primary factors controlling jadeite phase transitions and color development, providing crucial theoretical insights for jade quality assessment and provenance determination [45].

5.3. Speculation on the Cause of Formation of Guatemalan Blue Jadeite

The present study elucidates the multistage genesis of jadeite samples through mineral compositional discrimination and CL imaging techniques. The presence of abundant fluid inclusions, oscillatory zoning, and distinct concentric structures within CL images confirms its classification as a typical fluid-crystallization type (P-type) [1] jadeitite (Figure 12). This reflects direct crystallization from Na-Al-Si-rich fluids under high-pressure conditions (1.5–2.5 GPa) with thermal overprinting <400 °C. Within the CL images, characteristic oscillatory zoning and differential luminescence features manifest distinct episodes of jadeite formation (Figure 5a–d). Diagnostic absorption peaks for CH₄ (2915 cm⁻¹) and CO (2142 cm⁻¹) [22] identified within fluid inclusions (Figure 13) indicate the participation of reducing fluids derived from serpentinization processes during petrogenesis. Major element analysis reveals intermediate Na₂O contents between stoichiometric end-member jadeite (15.4 wt.%) and albite (11 wt.%), accompanied by progressive SiO₂ enrichment (ΔSiO₂ ≈ 2.3–4.7 wt.%). Combined with the clustered distribution of jadeite compositions within the Qz-Jd-Ab ternary diagram, these observations suggest chemical modification of primary jadeite through subsequent albitization, concurrent with the infiltration of Ca-Fe-Mg-rich fluids, resulting in the formation of pyroxene veins and poikilitic albite replacement textures.

X-ray fluorescence (XRF) elemental mapping reveals significant compositional heterogeneity across domains within the samples, indicative of multiple hydrothermal events. Distinctive enrichments in V, Fe, Ti, and Zn observed in banded regions compared to adjacent massive jadeitic zones (Figure 14), coupled with Fe-V enrichment within massive inclusions, collectively signify structural modifications caused by the infiltration of late-stage Fe-Zn-V-rich hydrothermal fluids. The presence of patchy inclusions further suggests non-equilibrium crystallization conditions, potentially associated with shear zone-mediated fluid interactions [45]. Consequently, the evolutionary model comprises three distinct phases: (1) Initial stage: formation of jadeite via slab dehydration within subduction channels; (2) Metasomatism by Fe-Ti-depleted fluids (Figure 15) coupled with trace element modification, manifested as green CL zones; and (3) Hydrothermal overprinting stage driven by Fe-Zn-V-rich fluids during shear zone activation.

6. Conclusions

The present study systematically elucidates the mineralogical characteristics, chromogenic mechanisms and genesis of blue jadeite from Guatemala. Utilizing a suite of analytical techniques including Raman spectroscopy and XRD, the samples were classified into two distinct phases: a jadeite-dominant “jadeite-phase” and an omphacite-rich “omphacite-phase”. The blue coloration is mainly attributed to crystal field transitions controlled primarily by Fe³⁺ (peak at 381 nm), with a secondary contribution from Fe²⁺→Ti⁴⁺ charge transfer, while the color intensity shows a positive correlation with Fe and Ti concentrations. The jadeite phase crystallized under high-pressure, low-temperature conditions, whereas the omphacite phase formed through metasomatic replacement by Mg-Ca-Fe-enriched fluids, involving coupled substitutions of Na⁺ by Ca²⁺ and Al³⁺ by Mg²⁺/Fe²⁺. Fluid inclusion analyses revealed the presence of CH₄ and CO, confirming a reducing environment and supporting its classification as a P-type jadeitite formed from Na-Al-Si-rich fluids derived from Na-Al-Si-rich fluids in subduction zones. These findings provide critical insights for gemological authentication and advance the understanding of the petrogenetic processes governing blue jadeite formation.