What a great crew. I was lucky enough to join these three Geochemists on a field expedition to the volcanoes: Brandur, Fontur, and Saxi to collect plagioclase xenocrysts and basaltic glass. They posed for me in front of this mountain of hyaloclastite, which formed in a sub-glacial eruption. #geology#Iceland#volcanology#hyaloclastite#geoswag
Hyaloclastite cemented with zeolites. When lava erupts under water, a lot of glass forms because of the rapid chilling of the lava. Much of this glass may break off and accumulate in depressions or between the lavas. The dark material here is the (basaltic) glass and the white material is the mineral zeolite, which precipitated between the glass fragments. The term "hyaloclastite" means "glassy fragmented rock". (The Icelandic coin is about the size of a dime.)
Subglacial pillow lava. Pillow lava is a type of lava that forms when usually basaltic lava erupts underwater. The name derives from the rounded pillow shapes taken by the lava. In Iceland, one often has volcanoes capped by glaciers. When the volcano emits lava, the bottom of the glacier may melt and the lava is emplaced underneath the glacier as pillow lava.