How can the fine details in a rock’s appearance and texture help us determine how the rock was formed? Objective Students will make observations on hand samples of the various rock types seen at Florissant Fossil Beds and will correlate the different rocks with their stratigraphic sequence and deposition. Background Main Rock Types Igneous : forms from the cooling & solidification of magma or lava. Mineral crystals are often formed in Igneous rock. Geologists can determine how quickly the magma or lava cooled by the crystal size. Intrusive forms beneath the earth’s surface i.e., Pikes Peak Gra Duration: 60 Minutes.