Geology Facts: Learn more about our planet's rocks and minerals with the s, pictures, and other educational materials. are especially useful for teaching children about earthquakes, volcanoes, and other natural phenomena. Pictures show geology in action, including volcanoes and avalanches. Geology lesson plans for kids include dinosaurs and rock formations. You can also use geology facts to teach your children about the Earth's crust. Rocks are the foundations of Earth's structure, but there are many types of rocks. In geology, rocks fall into three categories: igneous rocks, which solidify from molten magma, sedimentary rocks, and metamorphic rocks. Each rock type has its own distinct characteristics, and some of them are not even solid at all. Rocks are constantly changing, often from one type to another. This process is known as the rock cycle. Rocks contain varying amounts of different minerals and metals. The world is home to over 4, 000 types of minerals. Geologists study these combinations and their relationship to one another. The most common mineral is quartz, which forms many sandy beaches around the world. It is also incredibly hard. Many rocks have unique tastes. One mineral, halite, tastes like table salt. Rocks are also categorized by their density. They range from igneous to sedimentary. Some rocks are softer than others. They can change into metamorphic rocks when they are heated or squashed under pressure. Metamorphic rocks are harder than they were before, and are sometimes called marble or slate. The process of weathering can take thousands of years to complete. Other rocks can get damaged by wind, waves, and moving ice. Once they have been exposed to the elements, they are susceptible to earthquakes and other natural disasters.