Silicic volcanic rocks within the active volcanic zones of Iceland are mainly confined to
central volcanoes. The volcanic zones of Iceland can be divided into rift zones and flank
zones. Each of these zones contains several central volcanoes, most of which have
produced minor amounts of silicic rocks. The silicic rocks occur as lavas and domes or as
tephra layers, welded tuffs and ignimbrites, formed both in effusive and explosive eruptions.
They tend to be glassy or very fine-grained, containing small amounts of phenocrysts …