Because Granite Is Less Dense Than Basalt Continents

Granites may have biotite or other micas and might have a little hornblende but not very much.

Because granite is less dense than basalt continents.

Granite is very much less dense than basalt. Granite is less dense than basalt mainly because granite is made up of lighter mass minerals like quartz and feldspars without much in the way of heavier mass weightier mafic minerals like pyroxenes and hornblende. Granite is 70 silicon. Basalt is denser than granite because basalt is a an oceanic type of rock so it has had more pressure from the ocean making it denser than granite because granite is a continental type of rock.

All rocks of igneous origin consist of magma or molten earth that finds its way up to. The key difference between basalt and granite is that basalt is mostly occurring on ocean floors while granite is in the crust of the earth in all continents. Hope it helps you. In addition the rock beneath continents is made primarily of silicon rich minerals like granite and quartz which are less dense than the magnesium rich basalt beneath the oceans.

Basalt can form in a few days to months whereas granite plutons can take millions of years to cool and harden. Basalt is more common in oceanic crust while granite is more common in continental crust. This is why the continental crust mostly composed of granite floats on oceanic crust made mostly of basalt.