Unique Interstitial Textures within Coarse-Grained Jadeitite from Kazakhstan and Their Significance in Locality Identification

Abstract

Unique finer-grained interstitial textures, occurring as small blocks or irregular shapes of 0.15–10 mm, were found merging in the coarse-grained textures of Kazakhstan jadeitite. According to the mineral content, the interstitial texture could be classified into two types: Type I, consisting of almost all jadeite crystals, minor omphacite, and little analcime, and Type II, comprising mainly omphacite and analcime, with minor jadeite crystals. They both showed no obvious preferred orientation and have distinct boundaries with the coarse-grained textures but appear more transparent, with finer grain sizes and higher degrees of idiomorphism. The coarse-grained textures include granitoid textures and radial clusters. The granitoid textures formed by euhedral to subhedral prismatic grains usually show rhythmic zoning patterns and parallel intergrowths. Furthermore, fluid inclusions contain H2O and CH4, and it was supposed that the coarse-grained textures were formed by the precipitation of jadeitic fluids. However, perhaps due to the insufficient supply of the fluids or sufficient space, some interspaces were left among the coarser-grained jadeitite. Afterward, these interspaces were filled with precipitation of the successor H2O-richer fluids under a different P–T condition from that of the former coarser-grained jadeitite, and consequently, two kinds of interstitial textures formed. Such interstitial textures seem to appear only in Kazakhstan and therefore could serve as a typical visual identification feature of Kazakhstan jadeitite.