Diamonds are composed of carbon, and any additional chemicals found in a diamond are known as impurities. Nitrogen, hydrogen, and boron atoms are some of the most prevalent diamond impurities. Diamonds seem yellow due to nitrogen impurities. When exposed to air, light wavelengths between about 380 and 500 nanometers (nm) are absorbed by the nitrogen molecules, which causes coloration. Other common diamond impurities include oxygen, iron, calcium, and sodium. These elements are all found in the earth's crust and can become trapped within the gemstone during formation or processing. They can also enter diamonds when they are mined. For example, coal mines use explosions to remove chunks of rock containing diamonds. The noise from these explosions can shatter diamonds into pieces that contain those impurities. Some diamond manufacturers remove most of the existing impurities before cutting and polishing the stones. This process is called "purification." Other diamonds are not purified before being sold because removing excess nitrogen does not change the color or other physical properties of the stone. The amount of impurity in a diamond has no effect on its beauty or value. However, larger amounts of certain impurities may cause problems for jewelry made from the diamond. For example, if too much nitrogen is present in a diamond, it will appear blue instead of yellow. This color difference can be difficult to detect unless you know what to look for.