Why are felsic lava flows so much more viscous than mafic ones?

Magma are the hot molten materials that rises up towards the surface due to the increasing force from the depth. These magma when comes out to the surface then they are considered as lava.

The felsic lava are those in which the amount of silica and aluminium is very high. Due to this high silica content, the viscosity is high. The amount of silica present in magma or lava is directly proportional to the viscosity of magma or lava. The felsic lava due to its high viscosity flows sluggishly.

Whereas, the basic lava are those in which the silica content is significantly less. Iron (Fe) and Magnesium (Mg) is mostly present in this type of lava. As a result of which it flows easily without any difficulty.

This is the reason why felsic magma (lava) are more viscous compared to the mafic magma (lava).