Two other forms also occur. As unstable forms convert to stable forms they release radioactivity. Since only protons and neutrons have apreciable weight the atomic weight of an element is equal to the number of neutrons and protons. Isotopes have also been used to determine the age of the earth, because they act as natural clocks. We will study this when we look at radiometric dating methods.
Some isotopes are unstable and break down from one isotope to another.
Ions Atoms may carry a positve or negative charge depending on the number of electrons and protons. These are what we call ions. Cations are negatively chanrged, and anions are positively charged. Each mineral has a specific temperature of crystalliaztion. Growth rates of crystals are dependant on the composition of melt, temperature and viscosity of melt, and the presence of volatiles such as water.