double-chained silicate molecule that can support many different metal cations, like iron, magnesium, aluminum, calcium, and sodium. Micas are silicates that have sheets of polymers. These sheets explain why they are so flaky. Only chemical bonds called van der Waals forces, which are weak forces between molecules, bind these sheets together. Clays are also sheet silicates that have water within the molecular structure. Water keeps the sheets slippery with respect to one another. This is great for pottery making. Firing the clay drives the water out, leaving a sturdier product. Biotite and muscovite are both types of silicate micas. They differ in the number of cations in them. The muscovite has potassium and aluminum in it, while biotite has only magnesium and potassium in it. Quartz is just SiO2, which is balanced and not a charged ion. Feldspars have 25 percent of the silicon atoms replaced by aluminum. The charge is different so you need potassium, sodium, or calcium to make potassium feldspar or plagioclase feldspars. You should at least know what these main minerals look like: pyroxene, hornblende, muscovite, olivine, garnet, biotite, K-feldspar, quartz, and plagioclase. With these in mind, you can identify most surface rocks on earth.
NONSILICATE MINERALS Nonsilicate minerals are those that don't have the silicone and oxygen tetrahedral ion. These are less common but often extremely important to the world's economy. Iron, lead, copper, and other major metals come from the earth in various forms. There are different groupings of these —many of which you will recognize. The native elements are usually the precious metals, such as platinum, copper, gold, and silver. These can exist by themselves or bind in an ionic way to make another compound. Carbonates include dolomite and calcite. These are based on some salt that has the carbonate ion in it. Lime and cement are carbonates. Oxides are also common because oxygen seems to be highly reactive. It is also very abundant. Hematite is an oxide made from iron and oxygen, having the chemical formula Fe2O3. Magnetite comes from iron, and bauxite is an aluminum oxide. 86
