 Overall, the composition of sediment depends on the rock that's breaking down into the grains, the weathering processes that are acting on that rock, and then the transport of those grains and the weathering processes that happen along the transport path. So when we're looking at the composition of sediment, we can tell various amounts about the original rock and the transport processes. If a rock is mostly being physically weathered and just breaking down into smaller pieces, the composition of the sediment mirrors that of the original rock. So for example, if you have a granite that contains quartz and sodium and potassium feldsparer and biotite, the sediment that's produced will be class of granite. And when you have class of the original rock with multiple minerals and then we can call them lithic clasts, and then because it's coarse-grained, the individual minerals can also break out and you would expect to have sand grains because it's coarse-grained of quartz, feldsparer, and biotite, for example. So when you have physical weathering processes, the sediment mirrors the composition of the original host rock. The different grains can abrade differently and so you can lose some of the softer grains during abrasion, during transport. In contrast to physical weathering, during chemical weathering, you're transforming the rock composition, and so it's harder to tell what the original rock type was. There are some minerals in rocks, however, that are very resistant to chemical weathering and they don't dissolve and they don't alter very easily. And so those grains tend to persist during the transport process and form the bulk of sedimentary grains when you have a lot of chemical weathering. In contrast, there are other grains that are more reactive and those are the ones that disappear and new minerals form when they're being altered. So we can look at minerals that are common in igneous rocks, for example, and look at their propensity to react and alter into new grains. So start with the most reactive ones and we're going to go down to least reactive. So one of the most reactive minerals is olivine, particularly the type with iron in it. Olivine is stable at high pressures and temperatures and not very stable at low temperatures, low pressure and in the presence of water. The iron-rich olivine in particular has reduced iron so if there's oxygen around, it'll react as well. Magic lace or calcium feldspar is also very reactive and it reacts to clay. Again, it's a high temperature, high pressure mineral. Pyroxene, again the same way, these mafic minerals are not very stable in the presence of water. Mithiboles are common metamorphic minerals and it depends a lot on the details of their composition, how stable they are. They already are a little bit hydrous and so they tend to be a little bit more stable. So then sodium feldspar's tend to, again, react with the water but not as much as the calcium feldspar's. Biotite is a mica with iron in it and the oxidation of that iron in the presence of oxygen makes it a little less stable. Potassium feldspar is next on the list muscovite, again another mica but without the iron, it's a little bit more stable. And then the most stable common mineral against chemical weathering is quartz. And so the environment where you have chemical weathering going on, these minerals are beast-likely to persist and quartz is the most likely to persist. So in general on earth we have quite a bit of chemical weathering and quartz is one of the most common sedimentary grains that are present. Thanks for watching.