lava mafic lava basaltic lava 2013-05-05T16:56:29Z Mafic lava generally erupts at temperatures in excess of 950 degrees Celsius. The high temperature and low polymerisation in mafic lava favors low viscosity and chemical diffusion, promoting the formation of large, well-formed phenocrysts. Mafic lava is lava which, relative to other lava types other than ultramafic lava, has a high ferromagnesian content and low aluminium and silica content, with silca making up between 45 and 52 percent of its weight.