The peridotite plugs of Rum: Crystal settling and fabric development in magma conduits

► We argue the Rum peridotite plugs were conduits for olivine-phyric magma. ► The olivine microstructure formed by crystal settling. ► Porosity was reduced by grain re-arrangement and overgrowth. ► Comparison with the layered series points to a thin, non-compacting mush zone.