Strength of an ionic bond decreases as bond length increases. Ionic bonds predominate type in mineral structures. Chemical bonds in some minerals are intermediate between these two extremes. Fe 2 SiO 4 . Feldspar Show wide compositional range.
Different charges require shuffling other atoms to maintain electrical neutrality.
Mineral color can vary from specimen to specimen. Adding Ti and Fe to corundum produces the blue of sapphire . Olivine , pyroxene , and amphibole get deeper colors with increasing Fe content. Mineral Classification Minerals may be classified by the type of anion or anionic group they contain or by their crystal structure. Silicate minerals most abundant in Earth's crust and mantle.