Nonsilicate Minerals

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.

Sylvite is a potassium chloride salt, just like halite comes from sodium chloride. Lead, copper, and even mercury can have ores made with sulfur. A few of these are cinnabar and galena. Sulfates are used for many purposes. Epsom salts is a magnesium sulfatecontaining substance, and gypsum is a sulfate used to make sheetrock. Phosphates like apatite are the same thing as what you'll see in bones and teeth.

Calcite and dolomite are interesting because you see so much of it in sedimentary rocks, such as limestone and dolostone. The interesting thing about these is that they have a great many small fossils in them. Most are marine fossils. Look for seashells or crinoids in dolostones that date back to Precambrian times. A lot of calcite comes from the breakdown of seashells coming from ancient seas.

Calcite in crystalline form have birefringence, which means that light goes in and then splits to travel two different pathways. You will see double images of things that you see through it, which makes it a good tool for geologists. It actually polarizes light to make microscopes so you can study other rocks or minerals.

Notice how so many of these minerals are salts. Some will dissolve in water. The carbonates don't generally dissolve in water, which is a good thing since seashells are made from them. Calcite does not agree with acid, however, which is why a small bottle of hydrochloric acid should be in your geologist kit. All salts like this that are made when water evaporates are known as evaporite minerals.

Oxides are easy to spot, especially when oxygen mixes with iron. This is essentially rust and leads to the rust color of rocks in many parts of the United States. There are red cliffs made of sandstone in Utah that come from quartz that has been coated with iron oxide on the outside. Hematite, limonite, and magnetite are all forms of iron oxides. The formula is the same but the way they are connected will differ to make the varying appearances of these substances. Other interesting oxides include corundum, which is a type of aluminum oxide. Corundum is the base stone for both rubies and sapphires.

Sulfides have sulfur in them along with a metal ion. Iron pyrite is essentially iron sulfide or fool's gold. The mineral called chalcopyrite is a copper and iron sulfide. Galena is a lead sulfide used to make lead, and sphalerite makes zinc because it is zinc sulfides.

These sulfides all help to make the main minerals industrially, like lead, zinc, and copper. So many more of the important metals we get come from sulfide ores.

Phosphate is an ion that has a tetrahedral shape. It is easily mixed with other ions to make a phosphate salt. Apatite is a phosphate salt that mixes with fluoride, chloride, and calcium. Turquoise is a gemstone made from a phosphate that contains molecules of water and plenty of copper and aluminum.

Native elements can all produce minerals. Most of these are the metallic minerals like copper, platinum, silver, and gold. Diamonds are essentially the same carbon as you'll see in graphite. The only difference is that a lot of time and pressure went into making diamonds. This is why the interior core of the earth probably contains a lot of diamond material. Sulfur is a non-metallic substance you might see in its native form after it is emitted from volcanic fumaroles.