The mantle is the next layer of Earth. It is located between the crust and the outer core. The mantle is the thickest layer of the Earth's structure. It is 1,800 miles thick. Sine it is right next to the crust the lowest temperature it could be is 1,600 degrees Fahrenheit. However, near the bottom of the mantle it can reach up to 4,000 degrees Fahrenheit. Due to the hot temperatures rocks are at a heavy liquid state. You can compare this liquid to that of asphalt. It moves slowly because of the temperature difference. These moments are called convection currents. Convection currents can cause plates in the crust to move, which can result in earthquakes. The crust of the Earth floats on top of the mantle. There are not any rocks to collect at this layer of the Earth.
Due to the liquid state of the mantle you have no rocks to collect at this layer. You are here to simply observe what happens under the Earth. At this point you may begin to ponder what this layer has to do with rocks. Well, due to the movement in the mantle this is where the heating a cooling of the crust can come into play. Some igneous rocks are formed close to the mantle, and when a volcano erupts the liquid comes from the mantle. This can result in extrusive igneous rocks on the surface of the crust. You see, all of the layers of Earth are connected, which means they play some role in the formation of rocks. The formation of rocks is known as the rock cycle. Click the link to learn more about the rock cycle.