 Hello, this lecture coincides with the OpenGeology.org textbook created by authors at Salt Lake Community College, including myself. This lecture is covering silicates and how minerals are classified. There are well over 4,000 different named minerals that mineralogists have discovered so far. And fewer than 100 of these make up most of the rocks on the planet, so a lot of the minerals beyond that hundred are special cases. Most of the continental crust is made up of just eight different types of atoms, types of elements. And most of those, 46% by weight is oxygen, and another almost third is silicon. The silicon and oxygen are extremely abundant. And because of that, we separate minerals, classify minerals into two major groups. Today, we're going to talk about the silicates, which contain silica, a combination of one silica atom or oxygen atoms to make what is known as a silica tetrahedra. These account for more than 90% of Earth's crust. There are also non-silicates, which I will devote another lecture to, and we order these by the type of chemicals, type of elements in those. They're not as common as the silicates, but they're still definitely economically important. So the two major groups, a lot of people like to organize silicates by light silicates and dark silicates. And this coincides with the continental crust, which is more felsic in nature. That's an igneous rock compositional term. And the dark silicates coincide with the mafic oceanic crust. Light silicates, like the continental crust, are generally light, weight in specific gravity, and light in color. And they contain things like aluminum, potassium, calcium, and sodium, and relatively more silicate, silica material. And examples of minerals that are considered light silicates are quartz, potassium feldspar, which is pictured in this slide, muscovite, a sheet-like, semi-transparent mineral, and a lot of clays, kaolinite, things like that. Dark silicates are mafic, beautiful dark minerals, iron, and magnesium rich, relatively less silica than the light silicates. Of course they're silicates, so they still contain silica. They are denser, heavier, and some prime examples include the beautiful green olivine, peroxine, and amphibole. And there's some algae and biotite presented. Show you some examples of those dark silicates. All silica silicate minerals contain silica and oxygen. And there's a silica tetrahedra for you. It looks kind of like a pyramid, but you have nicely arranged oxygen atoms around a silica atom, four-charged oxygen atoms surrounding the silica atom. And you can polymerize, link together, polymer, what I think I want to hear polymerization is I think of plastics. They're polymers. They're polymers because they have long strings of carbons chained together. And this is a very similar idea. You have long strings of the silica tetrahedra. You can make very complicated and interesting structures based on how these silica tetrahedra are arranged. And this is how we organize a lot of the silicates, other than splitting them into light versus dark. You can organize them based on how the silica tetrahedra are arranged. The simplest situation being the nezzo silicates, which are on their own. Soros, I think that's a Greek root for sister where you have two conjoined silicate tetrahedra. You can get into more complex structures like chains and double chains. And these can create things like the asbestos type minerals that have these stringy strands. And you can start to see how the atomic scale arrangement of silica tetrahedra lead to the properties of the mineral. You get into these phylo silicates, which are sheet-like phylo, I think is a Greek root for a leaf. And you can get these amazing sheet-like silicates, the mycas, the books of single cleavage where they split into thin sheets, like a lipidolite or muscovite or biotite. And cyclosilicates, which are ring-like structures. So all of these are examples of polymerization, silicate minerals, and the different arrangements of these silica tetrahedrons will create for very different properties, especially how the minerals break and cleave and split into smaller pieces. And then the strongest and most orderly arrangement, kind of meta to play a YouTube video and a YouTube video. But here is the structure of silica, of quartz. And this is a framework silicate. You can see kind of a three-dimensional framework of these silica structures. And oftentimes you can have ions charged atoms connecting these silicate structures, these arrangements of silica tetrahedrons where you have these charged ions between your sheets or between your rings or within your rings. So keep that in mind. And that's part of what can make up the chemical composition of these silicates. And that's it for the silicates. Please continue watching for the non-silicates. And I hope you learned a little bit about