Number and location of electrons controls chemical behavior. Some atoms tend to gain electrons and become negatively charged anions . Other atoms tend lose electrons, forming positively charged cations . The resulting charge on an atom is its valence. 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.