For now, we will not be concerned with the core except to note that there is an outer liquid core and an inner solid core. The crust is enriched in oxygen, silicon, alumnium, potassium and sodium. The mantle is enriched in iron, calciuim and magnesium. The oceanic crust has a composition intermediate between the continental crust and the mantle. The Mineral Gallery offers a full text search ability which you will use to complete this exercise.
Plagioclase is concentrated in igneous rocks from the oceanic crust .
Olivine and pyroxene are both solid solution series and are common silicate minerals concentrated in the mantle. Minerals which have the same composition but different structures are polymorphs. Read the section on Specific Gravity. Define, in your own words, specific gravity. In general, high pressures favor higher densities and high temperatures favor lower densities.