WorldWide Drilling Resource

Graphite is a mineral which forms when car- bon is subjected to heat and pressure in the earth's crust and in the upper mantle. Graphite and dia- mond are the two mineral forms of carbon; and the two share the same composition, but have very different structures. Graphite is an extremely soft mineral and breaks into small, flexible flakes which easily slide over one another. This feature accounts for graphite’s greasy feel, a characteristic which makes graphite a good lubricant. Because it is a solid material, it is known as a dry lubricant, which makes it useful for applications where wet lubricants, such as oil, cannot be used. It is also the only nonmetal element which is a good conductor of electricity. Natural graphite is used mostly in refractory applications, involving extremely high heat. These account for the majority of the usage of graphite. One example is in the crucibles used in the steel industry. Additional uses for graphite are in brake linings, lubricants, and molds in foundries, as well as a variety of other industrial uses consumed each year. Lead penci l cores are made of a mixture of clay and graphite. Paper is marked by loosely cleaved graphite flakes, while the clay acts as a binding material. The higher the graphite con- tent of the core, the softer the pencil and darker its trace. There is no lead in what are known as lead pencils, but the name originated in Europe when graphite was cal led “plumbago” or “black lead” because of its metallic appearance. The mineral’s use as a marker dates from the 16th century in northern England, where local legend states shepherds used a newly discovered graphi te deposit to mark sheep. From 1890 to 1920, underground mining of graphite was practiced in New York and Pennsylvania. From 1942 until the end of World War II, only open-pit methods were used, because working weathered rock was relatively easy. Dur ing Wor ld War I I , graphi te was mined underground in Montana, but shor t l y thereaf ter, mining ceased because it was too costly to compete with Sri Lankan graphite. Madagascar operations are entirely open pit, but in Bavaria, Korea, Mexico, and Sri Lanka, the depth and physical characteristics of the deposits allows for underground mining to be practiced. Underground mining operat ions in Mexico exist 300-1300 feet below the surface, measured on the angle of the vein. Some of the older mines in Sri Lanka reached depths of over 1400 feet on a vertical plane. For many years, mining operations in Sri Lanka were primitive and ore extraction was slow and cumbersome, but the mines were mechanized after World War II. 15 WorldWide Drilling Resource ® FEBRUARY 2019 The World of Minerals MIN