The red crystal above is called rhodochrosite. Most of the best specimens of this striking gemstone, including the one in the photo, have been found in central Colorado. What are the properties of crystals? How are the atoms or ions that make up crystals arranged? What is responsible for the beautiful colors of minerals and gems? This chapter will reveal the answers to these questions, as you learn about the composition and properties of ionic compounds and of pure metals. In an ionic crystalline solid, positive and negative ions are arranged in an orderly, repeating fashion. The colors are contributed by various amounts of transition metal ions in the crystals. The red color of rhodochrosite comes from manganese(II) carbonate, MnCO3. Metals also have a crystalline structure, which contribute to the familiar properties of metals like malleability and electrical conductivity. We begin with a detailed look at how ions form.
Opening image courtesy of Sam Wise. CC-BY-NC-SA 2.0.