Graphite
Authors: Jarred Ashley, Jeffrey Benson, Dillyn Robinson
Mineral Name: Graphite
Chemical Composition: Carbon (C)
Color: Black to silver
Streak: Grey to silver
Hardness: 1-2
Cleavage/Fracture: 1 cleavage plane, breaks into sheets but can be hard to see as the mineral is sp soft that the plains can be distorted.
Crystal Form: Graphite forms in a hexagonal shape. The carbon atoms arranged in the graphite form hexagonally in a planar condensed ring system. Most commonly found in little pieces, large pieces are rare and hard to come across. The pieces are usually thin and flaky, with the exception of large thick pieces.(1)
Luster: Metallic
Special Features: It is considered both a metal and a nonmetal, while being a solid it is also a lubricant. (11) Specifically, graphite has a soft, greasy feel and easily leaves a grey streak on any surface.
Varieties: Varieties of graphite consist of cliftonite, uraniferous graphite, and amorphous graphite. Cliftonite can be found in iron and is known as a pseudomorph of graphite. A pseudomorph is a crystal consisting of one mineral that has taken the form of another. Uraniferous graphite is a uranium variety of graphite, and amorphous graphite is a very fine grained form of graphite.(2)
Mineral Group: Graphite belongs to the native elements, which includes minerals that contain only one single element, in this case carbon.. (5) Graphite also belongs to non-metallic elements, which is a group of minerals from the native elements that are not composed of metals and have no metallic properties. However, graphite is special because it has a metallic luster.. (1&6)
Environment: Graphite is found in metamorphic rock, sometimes in pegmatites, and hydrothermal veins. Pegmatites are a form of igneous rock that form at the end of a magma chambers cooling process when volatiles are concentrated in the magma causing cooling to slow and mineral texture to coarsen. Through the processes of hydrothermal activity, heated water dissolves the graphite and deposits it into veins in surrounding rock, this also provides more of a crystallinity and makes it more useful for electrical applications. (1&7)
Associated Rock types: Graphite can be found in metamorphic rocks like marble, quartzite, gniess, schist, and the sedimentary rock coal.
Occurrence in North America: There have been graphite mines in Alabama, Montana, Alaska, California, New York, New Jersey, Pennsylvania, Arizona and Quebec, Canada. (3)
Economic Uses: Graphite is mainly used in pencils. First, the graphite is put into a rotating drum with rocks so it can be crushed into a fine powder. Water is added to the powder and it is mixed for three days. Then all of the water is squeezed out, leaving a sludge that is put into a cabinet to air dry and harden for four days. Next a grinder is used to turn it into a fine powder again and water is added to make it a smooth paste. Then the paste is pushed through a small tube to form the rods, that are then cut into pencil-sized pieces and put on a conveyor to dry. They are then baked at 1,800°F, which makes the lead smooth and hard, then wood is cut into slats and small grooves are carved into each. Glue is applied to the wood slats and the lead is inserted into each slat, and another piece of wood is placed on top. One at a time the wood is cut into hexagonal, or round pieces, and the same machine also cuts the slats apart. Each pencil is sanded and given 5-8 coats of paint, a heated metal stamp then presses either paint or foil into the pencil, also indicating its hardness and company. Lastly the ferrule (the metal part of the eraser) is tightly fastened onto the end along with the eraser.(8)
Industrial Uses: Because graphite is soft giving it a greasy feeling, it can be used as a dry lubricant. Another common use of graphite is in refractory applications, which are applications that demand materials that can withstand high heat without melting are disintegrating. One such application occurs in steel mill crucibles (which are the melting buckets).(9)
First Notable Identification: It was first discovered before 1565, when the local farmers from the town of Grey Knotts of Seathwaite in Cambria, England found it much easier to mark the sheep they owned with the mineral. The mineral was named graphite in 1789 by Abraham Gottlob Werner which originated from the Greek word "graphein", which means "to write". (2) The Italians were first to use it in carpentry, although the graphite was flat and oval-like. The eraser for graphite was then patented in 1858.(4)
How We Identified It: We identified it because of its greasy feel and metallic shine. It has a very silvery definitive look to it, and with its hardness being so low and the color of its streak, writing on paper is the easiest way to identify it.
Don’t Confuse It With: Molybdenite, because of its lustrous appearance and its cleavage. It has a similar cleavage to micas (Cleavage: 1 plain) and also peels into sheets. It also has a similar streak, and color and has a greasy feel. Some of the notable differences are that molybdenite is more flexible, its crystal habit is flat and its fracture is uneven. Graphite will rub off into your hand, is extremely lightweight and has conchoidal fracture. (1&10)
Bibliography:
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“A History of the World - Object : The Graphite Pencil.” BBC, BBC, www.bbc.co.uk/ahistoryoftheworld/objects/AKHAcJoNQQ-DaYEz1dvZ9Q.
The Minerals and Gemstone Kingdom, www.minerals.net/mineral_glossary/native_elements.aspx.
The Minerals and Gemstone Kingdom, www.minerals.net/mineral_glossary/metallic_elements.aspx.
“Graphite.” GeoScience and News Information, geology.com/minerals/graphite.shtml.
“How A Pencil Is Made.” General Pencil Co., Inc., www.generalpencil.com/how-a-pencil-is-made.html.
“Graphite.” Minerals Education Coalition, mineralseducationcoalition.org/minerals-database/graphite/.
“Minerals.net.” Molybdenite: The Mineral Molybdenite Information and Pictures, www.minerals.net/mineral/molybdenite.aspx.
AZoM, Written by. “Graphite (C) - Classifications, Properties and Applications of Graphite.”AZoM.com, 1 Aug. 2017, www.azom.com/article.aspx?ArticleID=1630.