Why Is Crystal Structure Important?
Elements have very different properties depending on how they are stacked together or what other elements they are stacked together with. We wouldn't put salt (composed of sodium and chlorine) on our food if it tasted like the chlorine that we put into our swimming pools.
A great example of the importance of crystal structure is the difference between two minerals; graphite and diamond. Graphite is the soft, dark colored material that is found in pencil lead, while diamonds are very hard, often transparent and colorless, and very expensive gemstones. Both graphite and diamond are made out of only one element; carbon. The reason that graphite and diamond are so different from each other is because the carbon atoms are stacked together into two different crystal structures (see figure). Graphite is composed of carbon that forms loosely bonded sheets in their crystal structure. These sheets rub off easily to mark the paper when you write on it. Diamond is composed of carbon atoms stacked tightly together in a cubic crystal structure, making it a very strong material.
This shows us that it is not only important to know what elements are in the mineral, but it is also very important to know how those elements are stacked together.