Lava from this location is very variable and includes the three main types felsic, mafic and a mix of the two, intermediate. Mafic lava is relatively richer in magnesium and iron which oxidises into orangey/red iron oxide. Felsic is rich in feldspar and quartz and is generally lighter in colour. When the eruption is explosive the lava contains bubbles of gas which solidify as the lava cools. Lavas that cool fast have a fine grain appearance as large crystals do not have time to form. The origin of this lava is Snaefellsjokull, an ancient cone volcano. Over the millennia great fields of lava have built up at the foot of the volcano and the type of lava has varied over the eruptions. These rocks have been used to build a wall in the churchyard at Hellnir, Snaefellsness, Iceland.