Carbon is one of the few elements that occur in nature in its native or free elemental form. There are a number of forms of carbon, known as allotropes, which are composed of pure carbon atoms but are arranged in different crystal lattices. Some of these forms include hexagonal graphite, rhombohedral graphite, diamond, buckminsterfullerene, and amorphous carbon (not really a crystalline form). Most forms of carbon, excluding diamond, are black to grey-black in color. Depending on the amount of graphite, amorphous carbon, or other contaminating elements, diamond can be found in colors ranging from clear water white through shades of black, gray, yellow, red, orange, blue, and green.
Pure carbon is a relatively reactive element and combines directly with many chemical elements, especially those considered oxidizing agents. Carbon has a particularly strong affinity for oxygen either in the form of gaseous oxygen, or as oxygen contained in chemical combination with other elements. Its ability to combine with oxygen makes it both a powerful and useful reducing agent (a substance that donates electrons resulting in reduction of the charge of the ion or atom being reduced). As an example, solid carbon is used to reduce iron from its oxide (Fe+3 to Fe0) in the blast furnace or other similar processes in which metallic elements are reduced from their oxide ores.
The most important impact carbon has on the human race is the fact that carbon is the basic building block of life, as we know it. Every plant, animal, and everything in between that is alive is based on carbon. No form of life on the planet earth is without carbon in its structure. The entire science of organic chemistry, which is the study of carbon compounds, is based on carbon.