THE STRUCTURE AND COMPOSITION OF MICROSPHERES FROM THE KILAUEA VOLCANO, HAWAII

Microspheres from the plume of the Kilauea volcano. Hawaii, display pr eviously unrecognized structural and compositional features indicating that the spheres are concentrically differentiated and at least parti ally crystalline. The surfaces of some spheres display evenly spaced h exagonal, submicrometer grains whose compositions suggest that they ma y be spinels. Distinctive prismatic and dendritic structures on the su rfaces of the microspheres are remarkably consistent through the popul ation and indicate that the spheres have crystalline outer shells. Ind ications of chemical etching are present, probably from exposure to HF in the volcanic plume. The structures and compositions of the microsp heres suggest that they differentiated and then solidifed during rapid cooling, as they passed through the gradients of temperature, chemica l composition, and redox conditions established in the plume as air di luted the gaseous species evolved from magma.