So the second type of rock is called sedimentary rock. This is rock that is laid down in beds or strata. So you recognize strata, stratigraphy. Again, these relate primarily to sedimentary rocks. There's three or four different types of sedimentary rock. There's clastic rocks. These are rocks that are the products of weathering. So your things like sandstones, conglomerates, mudstones, these are all clastics. We have evaporites, these are when minerals are produced by the evaporation of a warm salty sea leaving the minerals behind. We have sedimentary rocks that are formed by biological or biochemical processes. >> For instance, we might talk about the carbonates like the calcium carbonate, the limestones, these are produced by animals that have shells, they die, their calcium carbonate shells sink to the bottom and solidify into layers >> There are also biological sedimentary rocks that are comprised of silica. These would be something like cherts, and these would be microfossils that produce silica shells. Then the fourth one is pyroclastic flows. These are flows that are erupted by volcanoes, travel and are laid down in beds. Now you can see I've underlined it in blue here, indicating that it's kind of a hybrid between igneous rock being an extrusive, erupted from the volcano, but it's also laid down in beds. So there may be instances where we may see ash deposits that are laid down as sedimentary layers embedded within mudstones or sandstones. These ash flows can be critical for dating the layer of rock because of the isotopes within those minerals. So here's a small sample of clastic sedimentary rocks. I've got a conglomerate here, you can see these very smooth, large pebbles embedded within this matrix of finer grain sands and this is a very large clastic rock. Here's another type of large clastic rock. This is a breccia. You can see it doesn't have as much matrix surrounding the individual pieces but these pieces are very angular. So they haven't had time to erode, as in a stream bed, such as you might see in this conglomerate. This is a sandstone here, you all have a sense of the size of sand, and that's exactly what happens here. The sand from a beach or a sand dune, wind blown sand, solidifies and produces these and you can see the layers of different colored sands within this sandstone. Here we have either a mudstone or a siltstone. Here, the individual crystals, minerals are so fine grained, that you can't see them with the naked eye. We also have an embedded shell within this fossil shell embedded within this clastic sedimentary rock. So here's a different type of sedimentary rock, this is an evaporite. This, again, is the halite, the sodium chloride crystals that we saw now in its rock form. You can see the large size of these crystals as the salty sea slowly evaporated away leaving the salt. So here, we are looking at the biochemical sedimentary rocks. We've got two examples of limestone here. This limestone is, comes from the Solnhofen deposit in Germany. This is where they've gotten the Archaeopteryx samples from, and this is also a limestone, it's much coarser and you can actually see the individual fossil shells that comprise that. This limestone is so fine grain that you can't, with the naked eye, see the individual crystals, the individual shells of the microscopic animals that have comprised this. But here, we can actually see these fossils and how the calcium carbonate shells have been sandwiched together and lithified to produce this biochemical sedimentary rock. This is the fourth type of quasi-sedimentary rock, this is a pumice. This is from an ash flow from a volcanic eruption. It's very light, it's got very porous structure to it, where gas bubbles were trapped at the time that this formed. There's also elements, small bits of glass here when this ash flow cooled very quickly but it was laid down in a bed as an extrusive volcanic igneous rock, so it's kind of this hybrid between a sedimentary rock and an igneous rock
