Mineral Versus Rock
January 14, 2007
The diversity of rocks and minerals to be found under our feet is large, and the variety of forms quite wondrous. Most of them have nothing to do with the organic aspects of our planet. A mineral is any naturally-occurring substance with a solid, crystal structure. Additionally, it must be inorganic and have a homogenous chemical structure. Rocks on the other hand can be mixtures, aggregates and even have organic origins. So we can see that telling the difference can be immensely difficult. In some minerals the crystalline structure is so fine to appear smooth, such as some forms of hematite, while some organic crystals such as sugar or urea look very mineral like. The same chemical composition can be arranged differently to form different minerals. Most any school child can tell you diamond and graphite are both carbon, but there are many other of these polymorphs -- both marcasite (dark organic looking nodules) and fools gold (bright golden nuggets) are iron sulfide. Thus, while a nugget of copper may look very organic, it's a mineral, while chalk is just a rock.