Basaltic magmas have a relatively low amount of silica.
A silicic magma, such as dacite or rhyolite, has a relatively high amount of silica. In pyroxene, silica tetrahedra form long chains. In amphiboles, silica tetrahedra form double chains. As a result, the chains fo pyroxene and amphibole crystals that are beginning to form become entangled . . . . The isolated silica tetrahedra of olivine do not become entangled . . . . .