The Zhanguohong agate from Beipiao (Liaoning province, China), which occurs in the intermediate–felsic volcanic breccias of the Early Cretaceous Yixian Formation, generally shows massive and banded structures, with red, yellow, and/or white layers or zones. Little research has been done on its mineralogical and gemological characteristics or its genesis. In this study, we present petrographic and spectroscopic constraints on the mineral composition and micro-texture of the silica matrix, as well as the ferruginous inclusions within the agates, in order to deduce the origin of the Zhanguohong agate. According to the microscopic observations, sandwich-like interlayered micro-granular quartz, fibrous chalcedony, and jigsaw quartz bands are common in the banded agates. X-ray diffraction (XRD) and Raman spectroscopic analyses revealed that all of the samples were mainly composed of α-quartz and moganite, with minor hematite and goethite. The moganite content (17–54 wt%) of the silica matrix decreases by varying degrees from the outermost to the innermost part of the banded agates. The crystal defects and ferric iron in the microcrystalline silica grains probably contributed to the moganite crystallization. The red, yellow, and orange zones are rich in hematite, goethite, and their mixtures, respectively. The ore-forming fluids fluctuated between acidic and alkaline within a temperature range of 100–200 °C and at a sustained positive Eh. Combined with the field observations, these results suggest that the multiperiod precipitation of the agates probably resulted from the episodic volcanic activity during the Early Cretaceous lithospheric extension in eastern China.

The gemological features and formation mechanism of chatoyancy in sapphires obtained from Shandong, China, are investigated.

High-temperature and high-pressure (HTHP)-treated diamonds have attracted attention all over the world due to their vivid colors. In order to explore a new method for the rapid and non-destructive identification of HTHP-treated diamonds, in this paper, five IaAB-type diamonds yielded in Russia were selected as the research object and treated with HTHP. The HTHP-treated diamonds were investigated by DiamondView^TM, cathodoluminescence, micro-infrared spectrometry (micro-IR), low-temperature photoluminescence (PL) spectrometry, and three-dimensional (3D) fluorescence spectrometry. The results show that under DiamondView^TM and cathode rays, the five samples were all non-phosphorescent with different luminous patterns, such as regular annular bands, multiple groups of intersecting linear stripes, or jagged stripes. In the low-temperature PL spectra, most HTHP-treated diamonds exhibited stronger luminescence peaks at 637 nm compared to 575 nm. But there were also exceptions, such as the purple-red sample showing the opposite luminescence peak. In the 3D fluorescence spectrum of the HTHP-treated diamonds, the fluorescence peak mainly appeared in the range of 440–450 nm, accompanied by a broad band of 350–500 nm and even longer wavelengths. Meanwhile, some samples also exhibited fluorescence peaks at longer wavelengths, such as 353 nm, 676 nm, and 665 nm. These results make it possible to identify HTHP-treated diamonds by using luminescence characteristics, providing a new method for the non-destructive and rapid detection of HTHP-treated diamonds.

The mineralogical characteristics and formation mechanism of the green phase within moss agate remain debated. With large quantities of green mineral inclusions, the moss agate from Fuxin (China) provides an excellent natural laboratory for resolving these issues. This study presents petrographic, spectroscopic, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA) data to determine the composition and texture of these green inclusions. The agate predominantly occurs in pores and fractures of andesitic breccias of the Lower Cretaceous Yixian Formation. Microscopic observations reveal various morphologies (filamentous, clustered, platy, globular, and irregular) and tones (light, dark, true, and yellowish green) of the inclusions. X-ray diffraction (XRD), infrared, Raman spectroscopic, and EPMA analyses demonstrate that the inclusions are rich in celadonite. Compositional or color zones are observed for both celadonite-rich regions and the agate. SEM imaging reveals euhedral celadonite crystals increase progressively in size across older-to-younger growth domains of each zone. The euhedral habits of celadonite, the systematic grain-size increase in celadonite-rich zones, and the zoned structure of the agate collectively suggest that the agate and celadonite within it precipitated from hydrothermal fluids.