Minerals are grouped based on their compositions. The largest group of rock-forming minerals on Earth are the silicate minerals. So all silicate minerals contain silicon and oxygen, and they make up about 90% of all of the minerals that are found in the Earth's crust. So this pie chart here shows the different types of silicate minerals that are found in the crust.
So the most abundant by far are the feldspars and quartz. Okay, so plagioclase feldspar and potassium feldspar, which is also referred to as orthoclase feldspar. So those three minerals make up the bulk of Earth's crust with smaller amounts of other silicate minerals as well. And only about 8% of the minerals in the Earth's crust are not silicate minerals. So silicate minerals are really kind of the most important group of rock-forming minerals.
All of the silicate minerals are based on this structure here. right? So silicate minerals are generally formed by igneous processes, by either the cooling of magma deep underground or the cooling of lava that has erupted onto the surface of the earth, so crystallizing directly out of molten rock.
This structure here is called a silicate tetrahedron, so that's this shape where you've got one atom in the center surrounded by four other atoms. So you've got four oxygen ions, negatively charged ions, and you've got one positively charged silicon ion in the center. So each of these oxygen ions are bonded with covalent bonds to the silicon ion in the center, and that fills that silicon ion's outermost shell.
So the bonds between the oxygen and the silicon in the silicate tetrahedron are extremely strong bonds. What this chart shows are some common silicate minerals and their silicate mineral group. So silicate minerals can be grouped based on the orientation of their silicate tetrahedron. So you can have single tetrahedra like the mineral olivine, you can have chains of tetrahedra like the mineral agite, double chains, sheets like the mica minerals, biotite and muscovite, or the three-dimensional framework type structure, which is what we would find for things like quartz and feldspar.
So basically what you should know here is that all of the silicate minerals contain these silicate tetrahedra that are just arranged in these different orientations and that gives us the different silicate mineral groups. So I don't expect you to remember these different types of groups, just know that all silicate minerals are based on silicate tetrahedra. So most minerals fall into one of these eight major classes, and the classes are based on chemical composition of the minerals within that class.
So we've seen the silicates. These are all based on that silica tetrahedron. Again, the most abundant types of minerals in the earth. Then we have carbonates. This is the mineral called calcite.
Carbonates all contain a carbonate anion, and these are basically the second most common type. of minerals in the crust, particularly this mineral here, calcite. I'm not going to go too much into detail on the rest of these. You can read about these in the textbooks.
Oxides are metal atoms that are bonded with oxygen. So what we see here is rust. Essentially, rust is different types of iron oxide, so iron that is bonded with oxygen in the atmosphere to form these rusty colored iron oxide minerals. Halides like the mineral fluorite, sulfides like the mineral pyrite or fool's gold, sulfate minerals, phosphate minerals, and then native elements like native copper.
That's what we see here. So copper metal. So what is a native element? It's essentially a mineral that is composed of just one type of element. Right.
So some elements tend to occur in their pure state where you just have a whole bunch of atoms of the same element. within that mineral. This is very common with metals, so native copper like we just saw.
Native iron, this is iron from an iron meteorite, so a piece of asteroid that came through our atmosphere and then landed on the surface composed entirely of iron. Other native elements would be precious metals, things like gold, silver, platinum. Also, the polymorphs graphite and diamond would technically be considered to be native elements, right? They're both composed purely of carbon. So that's what native elements are.
They tend to be rare, especially for the precious metals. Okay, so there are well over 5,000 individual named minerals. Luckily for us, there's really less than a dozen that are actually very common.
And this slide shows the seven most common rock-forming minerals. All of these minerals, except for the mineral calcite, are silicates. Okay, so calcite is a carbonate. We talked about these, so these are the most abundant minerals in the crust, the two types of feldspars and quartz. Amphibole and biotite are found within the crust in lesser amounts.
And then you have olivine and pyroxene. These two minerals make up the bulk of Earth's mantle. And then calcite, which is the only one, again, that is not a silicate.
This is a carbonate mineral. It's quite common in the crust. It forms the rock referred to as limestone.