| Abstrakt: |
Features that are visible in the rhyolitic lava flow at Obsidian Cliff include pristine volcanic glass (black), flow banding (marked by trails of small, gray and pink spherulites), coarse pink spherulites, and lithophysae (large tan cavities). For example, lithophysal cavities that occur in spherulite cores are interpreted to be preexisting vesicles around which spherulite crystallization proceeded ([9]). Spherulites are clusters of radiating crystals, generally alkali feldspar and quartz polymorphs, that form either partial or complete spheres and are most distinct when present in obsidian. Compositional gradients surrounding spherulites in obsidian and their relationship to spherulite growth and lava cooling. [Extracted from the article] |
