Textures and whole-rock chemistry, as well as mineral composition, were analyzed in megaspherulites (high-temperature crystallization domains [HTCDs]) that formed in different geographical and geotectonic contexts and during different geological periods (Silver Cliff, CO, USA—Paleogene; El Quevar, Argentina—Miocene; Meissen Volcanic Complex, Germany—Late Carboniferous). All of these megaspherulites have formed exclusively in rhyolitic lava, and their mineral composition is dominated by K-feldspar (sanidine) and SiO₂ phases (quartz, cristobalite, tridymite). All megaspherulites represent composite HTCDs, comprising three zones: inner domain (ID), outer domain (OD), and a marginal domain (MD). Early evolution of megaspherulites is characterized by either central cavities and sector- to full-sphere spherulites or dendritic quartz-sanidine domains. The latter consist of bundles of fibrils each radiating from a single point reflecting relatively high growth rates. A common feature of OD and MD of all three megaspherulite occurrences is autocyclic banding. It mainly comprises fibrous (≤ 100 μm length), radially oriented sanidine and quartz, which formed at a temperature close to glass transition temperature (T_g). The termination of megaspherulite growth is marked by centimeter-sized sector-sphere spherulites on the surface. Megaspherulite formation requires limited nucleation, which is probably related to the low phenocryst content of the hosting lava. Latent heat from overlying crystallizing lithoidal rhyolite maintained low undercooling conditions keeping nucleation density low and facilitating high diffusion and growth rates. Late megaspherulite growth and its termination under low diffusion conditions is controlled by cooling close to T_g. Calculations based on literature data suggest that the megaspherulite growth presumably lasted less than 60 years, perhaps 30 to 40 years.

分析了在不同地理和大地构造背景下以及在不同地质时期形成的巨型球晶（高温结晶域[HTCDs]）的质地，全岩石化学以及矿物成分（Silver Cliff，CO，USA-Paleogene;阿根廷的埃尔奎瓦尔-中新世；德国的迈森火山综合体-石炭纪晚期）。所有这些大球晶仅在流纹岩熔岩中形成，其矿物成分主要由钾长石（山san）和SiO _2组成。相（石英，方石英，鳞石英）。所有大球晶均代表复合HTCD，包括三个区域：内部区域（ID），外部区域（OD）和边缘区域（MD）。巨球晶的早期演化的特征是中心腔和扇形至全球形的球晶或树枝状石英-山梨晶畴。后者由成束的原纤维束组成，每个束都从一个点辐射，反映出较高的增长率。所有三个大球晶出现的OD和MD的共同特征是自环谱带。它主要由纤维（长度≤100μm），径向取向的Sanidine和石英组成，它们在接近玻璃化转变温度（T _g）。巨球晶生长的终止特征是表面上的厘米大小的扇形球晶。球晶的形成需要有限的成核作用，这可能与寄主熔岩的低表晶含量有关。来自上层结晶的类晶流纹岩的潜热保持较低的过冷条件，从而保持较低的成核密度并促进较高的扩散和生长速率。晚期球晶的生长及其在低扩散条件下的终止通过冷却至接近T _g来控制。根据文献数据进行的计算表明，大球晶的生长大概持续了不到60年，也许是30至40年。