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Urban color represents the visual skin of a city, embodying regional culture, historical memory, and the contemporary spirit. However, while the existing studies focus on pedestrian-level facade colors, the “fifth facade” from a bird’s-eye view has been largely overlooked. Moreover, color distortions in traditional remote sensing imagery hinder precise analysis. This study targeted 56 Chinese coastal cities, decoding the spatiotemporal patterns of their fifth facade color (FFC). Through developing an innovative natural color optimization algorithm, the oversaturation and color bias of Sentinel-2 imageries were addressed. Several color indicators, including dominant colors, hue–saturation–value, color richness, and color harmony, were developed to analyze the spatial variations of FFC. Results revealed that FFC in Chinese coastal cities is dominated by gray, black, and brown, reflecting the commonality of cement jungles. Among them, northern warm grays exude solidity, as in Weifang, while southern cool grays convey modern elegance, as in Shenzhen. Blue PVC rooftops (e.g., Tianjin) and red-brick villages (e.g., Quanzhou) serve as symbols of industrial function and cultural heritage. Economically advanced cities (e.g., Shanghai) lead in color richness, linking vitality to visual diversity, while high-harmony cities (e.g., Lianyungang) foster livability through coordinated colors. The study also warns of color pollution risks. Cities like Qingdao exposed planning imbalances through color clashes. This research pioneers a systematic and large-scale decoding of urban fifth facade color from a remote sensing perspective, quantitatively revealing the dilemma of “identical cities” in modernization development. The findings inject color rationality into urban planning and create readable and warm city images.

In situ Raman spectra of aqueous K2WO4-HCl, K2WO4-HCl-NaCl, and K2WO4-CO2-NaCl solutions were collected at elevated temperature (T, 100–400°C) and constant pressure (P) of 30 MPa. The stretching vibration band of the W=O bond (v1) was analyzed to reveal the species of tungsten (W) responsible for the hydrothermal transport of W during mineralization. Results showed that monomeric tungstates with v1(W=O) bands at ~930 and 950 cm-1 are the dominant W species in weakly alkaline (room temperature, pH=7.7) to near-neutral (room temperature, pH=7.2) solutions under the investigated T‐P conditions. Overall, the stability of polymeric tungstate species with v1(W=O) bands at ~965–995 cm-1 decreases with rising temperature and was not detected at ≥300°C in moderately acidic solution (room temperature, pH=4.9). However, increased fluid acidity and salinity obviously enlarged the temperature stability field of polymeric tungstate species. In highly acidic solution (room temperature, pH=1.4), polymeric tungstates are the only stable W species even at 400°C. In the presence of 1.9 mol/kg NaCl, polymeric tungstate(s) can persist to at least 350°C in moderately acidic solution. Considering that 300–350°C is the major W-mineralizing T range and W-mineralizing fluid is generally characterized by a moderately acidic nature, we propose that, in addition to monomeric tungstates, polymeric tungstates can also be important W species in some natural geological fluids that are responsible for the mineralization of W. Future studies of the W mineralization mechanism should take this issue into account.

Sulfate is traditionally considered to have retrograde solubility in aqueous solutions. However, our recent hydrothermal diamond-anvil cell (HDAC) experiments have shown that the solubility of Na SO changes from retrograde to prograde in the presence of silica, leading to the formation of sulfate-rich solutions at high temperatures, in line with observations on natural geofluids. In this study, we use synthetic inclusions of fused silica capillary capsules containing saturated Na SO solutions and Na SO crystals to quantitatively investigate the solubility of Na SO at different temperatures in the Na SO -SiO -H O system. Sulfate concentrations were measured using Raman spectroscopy and calibrated using Cs SO solutions with known concentrations. The solubility of crystalline Na SO dropped slightly when heated from 50 to 225 °C and dramatically from 225 to 313 °C. At 313 °C, the Na SO crystals began to melt, forming immiscible sulfate melt coexisting with the aqueous solution, with or without solid Na SO . With the formation of sulfate melt, the solubility of Na SO was reversed to prograde (i.e., solubility increased considerably with increasing temperatures). The solubility of Na SO in the measured solution was significantly higher than that predicted in the absence of SiO over the entire temperature range (except for temperatures around 313 °C). This indicates that the presence of SiO greatly changes the dissolution behavior of Na SO , which may be caused by the formation of a sulfate–silicate intermediates such as Considering that most crustal fluids are silica-saturated, the solubility curve of Na SO obtained in this study can better reflect the characteristics of geofluids when compared to that of Na SO -H O binary system. At temperatures of 313–425 °C, the solubility of Na SO increases with temperature following the function = –3173.7/ + 5.9301, where and represent the solubility of Na SO in mol/kg H O and temperature in Kelvin, respectively. As an application, this temperature-solubility relationship can be used to evaluate the sulfate contents in fluid inclusions that contain sulfate daughter minerals, based on the temperature of sulfate disappearance obtained from microthermometric analysis. The sulfate concentrations of the ore-forming fluids of the giant Maoniuping carbonatite-related rare earth element (REE) deposit (southwest China) were calculated to be 4.67–4.81 (mol/kg H O). These sulfate concentrations were then used as internal standards to calibrate the previously reported semi-quantitative results of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of REE-forming stage fluid inclusions at this deposit. The calculated Ce concentrations in the REE-mineralizing fluid range from 0.42 to 0.49 wt%. The high fluid REE contents suggest that the sulfate-rich fluids are ideal solvents for REE transport. A mass-balance calculation was carried out to evaluate the minimal volume of carbonatite melt that was required for the formation of the giant Maoniuping REE deposit. The result indicates that the carbonatite dikes in the mining area are enough to provide the required fluids and metals, and thus a deep-seated magma chamber is not necessary for ore formation.

In situ Raman spectra of aqueous [K.sub.2]W[O.sub.4]-HCl, [K.sub.2]W[O.sub.4]-HCl-NaCl, and [K.sub.2]W[O.sub.4]- C[O.sub.2]-NaCl solutions were collected at elevated temperature (T, 100-400[degrees]C) and constant pressure (P) of 30 MPa. The stretching vibration band of the W=O bond ([v.sub.1]) was analyzed to reveal the species of tungsten (W) responsible for the hydrothermal transport of W during mineralization. Results showed that monomeric tungstates with [v.sub.1](W=O) bands at ~930 and 950 [cm.sup.-1] are the dominant W species in weakly alkaline (room temperature, pH = 7.7) to near-neutral (room temperature, pH = 7.2) solutions under the investigated T-P conditions. Overall, the stability of polymeric tungstate species with [v.sub.1](W=O) bands at ~965-995[cm.sup.-1] decreases with rising temperature and was not detected at [greater than or equal to]300[degrees]C in moderately acidic solution (room temperature, pH = 4.9). However, increased fluid acidity and salinity obviously enlarged the temperature stability field of polymeric tungstate species. In highly acidic solution (room temperature, pH = 1.4), polymeric tungstates are the only stable W species even at 400[degrees]C. In the presence of 1.9 mol/kg NaCl, polymeric tungstate(s) can persist to at least 350[degrees]C in moderately acidic solution. Considering that 300- 350[degrees]C is the major W-mineralizing T range and W-mineralizing fluid is generally characterized by a moderately acidic nature, we propose that, in addition to monomeric tungstates, polymeric tungstates can also be important W species in some natural geological fluids that are responsible for the mineralization of W. Future studies of the W mineralization mechanism should take this issue into account.

In situ Raman spectra of aqueous K 2 WO 4 -HCl, K 2 WO 4 -HCl-NaCl, and K 2 WO 4 -CO 2 -NaCl solutions were collected at elevated temperature ( T , 100–400°C) and constant pressure ( P ) of 30 MPa. The stretching vibration band of the W=O bond ( v 1 ) was analyzed to reveal the species of tungsten (W) responsible for the hydrothermal transport of W during mineralization. Results showed that monomeric tungstates with v 1 (W=O) bands at ~930 and 950 cm -1 are the dominant W species in weakly alkaline (room temperature, pH = 7.7 ) to near-neutral (room temperature, pH = 7.2 ) solutions under the investigated T ‐ P conditions. Overall, the stability of polymeric tungstate species with v 1 (W=O) bands at ~965–995 cm -1 decreases with rising temperature and was not detected at ≥300°C in moderately acidic solution (room temperature, pH = 4.9 ). However, increased fluid acidity and salinity obviously enlarged the temperature stability field of polymeric tungstate species. In highly acidic solution (room temperature, pH = 1.4 ), polymeric tungstates are the only stable W species even at 400°C. In the presence of 1.9 mol/kg NaCl, polymeric tungstate(s) can persist to at least 350°C in moderately acidic solution. Considering that 300–350°C is the major W-mineralizing T range and W-mineralizing fluid is generally characterized by a moderately acidic nature, we propose that, in addition to monomeric tungstates, polymeric tungstates can also be important W species in some natural geological fluids that are responsible for the mineralization of W. Future studies of the W mineralization mechanism should take this issue into account.