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 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.

The green Manas nephrite from Xinjiang (China), predominantly composed of felted tremolite fibers and typically occurring at contacts between serpentinized ultramafic rocks and enclosing basaltic–andesitic volcanics, contains diverse veins (including folded, Stage 1 straight, and Stage 2 straight varieties exhibiting ptygmatic, reticulate, and master-branching patterns, respectively) and spheroids (Type 1 and Type 2). Its provenance identification criteria have not yet been well established. This study presents geological, petrographic, and mineral chemical data from these veins and spheroids to constrain their mineral composition and texture. EPMA data indicate that the veins and spheroids are mainly composed of tremolite–actinolite fibers. The fibers in the Stage 2 branching veins are (sub-)parallel to the vein walls, whereas those in the other veins are (sub-)perpendicular to the walls. Type 1 spheroids are composed of felted fibers and commonly occur as breccia lenses within a nephrite matrix. In contrast, Type 2 spheroids are characterized by parallel-arranged fibers. The distinctive occurrence of the white (or gray) folded veins and spheroids serves as an important diagnostic criterion for provenance and is crucial for distinguishing the Manas nephrite from that of other localities.