Owing to the high market values of natural sunstones in Oregon, a kind of artificially diffused red feldspar exhibited at the Tucson Exhibition at the beginning of this century, whose color origin is the same as that of natural sunstone (copper nanoparticles). However, the details of the artificial diffusion process are less disclosed, there is no systematic method to obtain such gemstones. In this paper, we developed the high-temperature copper diffusion process for the surface recoloring of faceted labradorites, which are partly buried in the diffusant. By optimizing the experimental parameters of high-temperature copper diffusion, we successfully recolored the faceted labradorites to red and light red. The gemological and spectroscopic characteristics of the recolored faceted labradorite were further characterized. The red and light-red faceted labradorites exhibited the unique surface plasmon resonance absorption peaks of copper nanoparticles near 580 nm, which is the origin of red color. The typical inclusions formed in the faceted labradorite is in the shape of “fire cloud”. The interface of red and light-red faceted labradorite that is in contact with the diffusant is less contaminated, we believe that the contamination could be further reduced or eliminated by optimizing the high-temperature copper diffusion process. The way that the sample is in contact with the diffusant partly is versatile and promising in the surface treatment of materials that have already been processed.

In recent years, some sapphires were found to fade in sunlight and to increase their color after UV irradiation. This unstable color phenomenon is attributed to the photochromism of corundum. The photochromic effect seriously affects the grading and evaluation of sapphires, although its mechanism is still uncertain. Here, we performed a set of photochromic experiments on sapphire specimens using a 254 nm shortwave UV light source and a D65 light source (which simulates sunlight) to generate different color states exhibiting characteristic absorption, emission, and excitation spectra. We observed that, for different color states, variation in the intensity of the absorption band at ~460 nm was consistent with that of orange fluorescence at 500–800 nm. This observation indicates a relationship between color instability and orange fluorescence. Peaks in excitation spectra at 320, 420, 490, 560, and 637 nm provide insight into the source(s) of excited orange fluorescence, which are related to different types of F-centers and Mg-trapped holes. We propose an explanation for the photochromic phenomenon: the color of photochromic yellow sapphire is the result of a variety of defects that release orange fluorescence simultaneously. Further, we hypothesize that the mechanism of photochromism in yellow sapphires is linked to electron transfer between F-centers and Mg-trapped holes.

The debate of hydrous and anhydrous mafic magmatism in the Emeishan large igneous province (ELIP) requires more robust petrological and mineralogical evidence. This paper reports zircon U–Pb ages, clinopyroxene and hornblende major element compositions, whole-rock geochemical and Sr–Nd–Pb isotopic data of hornblende-rich mafic plutonic rocks from the Xinhe igneous complex in the central ELIP to address this issue. Analytical results indicate that the Xinhe mafic rocks were emplaced at 260–259 Ma, consistent with the main eruptive phase of the ELIP. The Xinhe mafic rocks can be divided into hornblende gabbro and gabbroic diorite based on petrographic characteristics and MgO content. The Sr–Nd–Pb isotopic signatures of Xinhe mafic rocks are indicative of an EMI-type enriched mantle source, which is similar to the adjacent contemporaneous Miyi layered intrusions and basalts in the ELIP. The Xinhe mafic rocks exhibit a hydrous-type crystallization sequence (clinopyroxene–hornblende+plagioclase), which contrasts markedly with the anhydrous-like olivine+plagioclase–clinopyroxene sequence documented in the Miyi layered intrusions. This difference records contrasting magmatic water conditions during crustal magmatic evolution, although water enrichment during differentiation, differing pressure–redox histories, and fluid interaction may also contribute to the observed assemblages. Mantle-source water heterogeneity remains a plausible interpretation that requires independent confirmation.