The arrangement of the silicon-oxygen tetrahedra in ferromagnesian silicate minerals is typically?
They don't have a 'typical' arrangement. The arrangement is specific to the mineral group concerned. Examples: In the olivines, the silica tetrahedra are totally isolated from one another by Fe and Mg ions, The pyroxenes are formed of single chains of silica tetrahedra. The amphiboles are formed of double chains of silica tetrahedra. In the micas the silica tetraheda are in sheets. All of these mineral groups have common rock-forming ferromagnesian variants.