Narrator: The Earth's surface is made out of rocks. These rocks are made out of different minerals. Each mincral of only one substance Minerals usually come in the form of crystals. Crystals like quart olivne, and diamond Crystals usually form when rocks melt at high temperatures and gradually cool down. Salt crystals, for example, are made from chlorine and sodium atoms. These atoms make very small cube. It's called a unit cell, When many unit cells come together, as though making a bigger cube, they make a crystal. This process is called crystallization Crystals come in all kinds of different shapes and colors. And they have many uscs, some crystals, like diamonds, rubies, and topaz, are hard to find, and beautiful to look at People wear them as jewelry. Some people b that crystals have the ability to change our feelings and provide protection from bad energy. People use other crystals as parts of modern machines. They make certain types oftechnology, like solar cells, work There are about 3,500 different minerals in the world Each of them comes in the form of a crystal. At first, they all look different However, mineruls belong to different families. A crystal's family depends on the shape of the mineral's crystals To tell them apart, we have to look at the shape of cach crystal's unit cell These unir cell patterns arc called crystal systems So thr, scientists have only tound one of evidence of seven unique crystal systems. In perfecr conditions, the crystal follows these patterns exactly But in the real world, crystals all have a unique look.