Biochemical sedimentary rocks, as the name indicates, contain material that has been made by life. So when we look at biochemical sedimentary rocks, the first thing we're going to look for are fossils. So when we're holding the rock, we're going to ask ourselves, is there fossils present in this rock? And we have two different variations of fossils that we will see or not see. The first is microscopic. These will be the ones that are not seen with the naked eye or even the hand lens, because they are too small. And the second category is large. We will either have fragments or whole fossils within the rock. So if we're holding a biochemical sedimentary rock that has microscopic fossils of things like plankton shells, how do we know that they're in there? Because when we hold the biochemical sedimentary rock, it doesn't look drastically different than the classic sedimentary rock that is comprised of just mud-sized grains. The great thing about the biochemical sedimentary rock is that the microscopic shells are made out of kelsite. So if I take the hydrochloric acid and I put it on the classic sedimentary rock, it is not going to have any reaction whatsoever. The mineral kelsite is not one of the major components making up this rock. Whereas if I take the biochemical sedimentary rock that contains microscopic fossils and I put acid on the surface, we will see bubbles or effervescing the reaction of that kelsite to the hydrochloric acid. One other additional feature to look at to determine the difference between the fine-grained clastic sedimentary rock and our biochemical rock containing microscopic fossils, when we look at the biochemical rock, there's no real structure to it. It's a big solid, massive lump that doesn't really have any distinguishing characteristics. Whereas when we look at the classic fine-grained rock, one side might be big, massive, and smooth, but on the other sides we're seeing layering, stacking up of sediment over time, something very characteristic of classic rocks. So if we get that reaction with acid and we see just a big, massive piece, we really want to start to lean towards biochemical sedimentary rocks with microscopic fossils. When we look at large fossils in the rock, they are going to stand out right away. So here we can see imprints of shells, we can see branches of coral, there are signs of life all throughout this rock preserved in this case as whole fossils, very easy to see and identify. The second category for biochemical rocks are those that contain or originated as plant matter. So here we're looking at the original plant debris being altered into coal. And when we meet and look at samples in the lab, we're looking at a variety of coal that is going to be black in color in very light weight in our hands. So even though this started as leaves and bits of plant matter, grass and whatnot, we are seeing that that has been compressed heated slightly and altered into the state that we see the black variety of coal called betuminous coal that we're holding in our hands. And you can see it's a little powdery, some of it comes off on the finger and then in your hand it's extremely light in weight. Because the plant debris was building up over time, we can see some stacking or layering in the side. And there are shells which are the classic sedimentary rock that has just mud-sized grain that can be black in color. So how do you tell the difference between is this coal that I'm holding or is it a black colored shell that I'm holding, it's the weight. The shell, quite heavy for its size, you know, it's about what you expect for a rock whereas the coal, extremely light, much lighter than you would expect a rock to be when you hold it in your hands. These are the characteristics that we are going to look for and identify while we go through biochemical sedimentary rocks.