 So I want to talk about the alteration of olivine and plagioclase because they both create common alteration mineral products as in clays and oxides. So I'd like to talk about plagioclase weathering first. So we have calcium, aluminum, silica on oxygen and it reacts with acidity to form calcium ions and the clay mineral kaolinite, which has yield to Si2O5OH4. So I need to balance this. So I have my calcium's okay, my aluminum's okay, silica's okay, I have nine oxygens on this side and only eight on this side, so I need to add a water and I have two charges on this side and only one on this side. So now we have four protons. So basically what this reaction shows is that plagioclase plus acidity forms calcium ions plus kaolinite easily. And so when you react the plagioclase here, it changes the pH of the water and it produces these kaolinite clays. And so there's this confusion or a mixture between clay-sized grains and clay mineralogy grains because they were named before scientists could actually tell the mineral structure from the grain size. But one of the interesting things about this is these are clay-sized in addition to being clay minerals. And so here the resulting product almost always produces a lot of suspended sediment. So we can also weather olivine and the acidity helps with that as well. And the iron in the presence of acidity will dissociate with the silica and you get two reduced iron and then the silica can also be in solution if it has enough protons. You have to basically replace the four charges with the ions with the protons here. And so we need four protons. So I have my charges balanced and I have my elements balanced here. So this iron will react with oxygen. So I'm going to use four of them to balance out the equation. And the reason for that is each one of the irons goes from two plus to three plus. And so if we have four electrons we can use one oxygen here. And then we're going to need some water to provide some extra oxygen. And the iron will oxidize to an iron oxyhydroxide, but I'm just going to use hematite here because it's a nice mineral phase, it's a little cleaner. And so this iron is in the three plus state. And so we actually, there are two of them in each one, so I need a two here. And then that means that I have three or six oxygens. So I have two here and so I need four more here to get six oxygens. And that leaves me with eight protons and I also need something to balance the charge. And so we end up with eight protons here. So we are charge balanced, we're oxidative state balanced, and we're element balanced. So one of the things that happens that's really interesting in this process is that when you oxidize the iron, you produce acidity. Some of you might have heard about the problems with acid mind drainage. That occurs when you expose iron two plus to water and oxygen at Earth's surface and it oxidizes to produce all these protons. If we look at the reaction of the olivine as a whole, this first part of the olivine weather and consumes protons and the second part produces them. So we can combine these two equations to have both the dissolution of olivine and the oxidation of iron. So I'm going to multiply this equation times two. So I have two olivines, eight protons, four irons, and two hydrated silica. When I add these two equations together, we basically now have eight protons and eight protons so we can get rid of those two. We have four irons and four irons so we can get rid of those two and everything else stays the same. So we end up with two olivines and on this side we need plus an oxygen plus four water molecules. Then we have our products on the other side. This canceled out with this. We have two hydra silicas and two hematite. So basically our olivine, when it's exposed to water and oxygen, goes into hydrated silica and hematite. Now again, this hematite is not a clay mineral but it's often clay sized. So it ends up in suspension in the water and this silica often goes into clay minerals but it requires other mineral reactions to actually form these minerals because the clay minerals all have aluminum in them and olivine doesn't have that aluminum. It's also possible that this could form microcrystalline quartz or chert or hydra silica like opal is a hydra silica mineral. So when you have pyroxenes and amphiboles they also release oxides if you have oxygen present and silica and aluminum to form these alteration products. So in summary the composition of sediment consists of lithic clasts of the original host rock if they haven't had time to alter. The least reactive minerals, quartz in particular is most common and then alteration and weathering products and those are mostly clay minerals and oxides. If you have very little chemical weathering you can have some of these more reactive minerals present but through time with alteration and exposure to water and oxygen they will disappear. So the composition of the sediment can give you a really interesting history about the protolith of the rock that formed the sediment, the weathering processes and how long and what types of weathering they've experienced. Thanks for watching.