The nature of magnetic single domains in volcanic glasses of the KBS Tuff

Magnetic and optical variations in volcanic glasses of the East African Rift have been investigated by means of experimental and analytical study. The results add to the formal understanding of magnetism in volcanic glasses and give us new perspectives on the nature, origin, and significance of fine-grained magnetic minerals and on the magnetic petrology of glassy rocks. The samples that we have studied in detail, glass shards from the KBS Tuff of northern Kenya, contain a superparamagnetic precipitate of microcrystals, ~2 to ~10nm in size. We interpret magnetic and ESR results to infer the possible existence of microcrystals or amorphous clusters of Fe atoms, ~1nm or smaller, in KBS glasses that appear homogeneous in high-resolution TEM images. Results from optical absorption experiments show that the color variations in KBS shards arise due to optical absorption by the precipitate, a result consistent with classical electromagnetic theory. -from Authors