4 Intrusive Igneous Rocks Magma is the term for any molten silicate material, whether below the surface or on top. Magma that is injected and crystallized below the surface forms intrusive igneous rocks . Mafic Andesite Diorite Intermediate Rhyolite Granite Felsic Ultramafic rocks are almost entirely ferro-magnesian minerals. Ultramafic extrusive rocks are very rare and most ultramafic rocks are the residue of partial melting.
Mafic rocks contain roughly equal amounts of ferro-magnesian minerals and calcic feldspar.
Felsic rocks contain minor ferromagnesian minerals, abundant quartz and both Na and K feldspars. Igneous rock compositions change as the result of partial melting and fractional crystallization . Mafic magmas are typically hotter than felsic magmas. Igneous bodies commonly have fine grained chilled margins and coarser-grained interiors.