Graphite

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One of the allotropes of carbon. Unlike diamond, graphite is a conductor, and can be used, for instance, as the material in the electrodes of an electrical arc lamp.

The pi orbital electrons delocalized across the hexagonal atomic sheets of carbon contribute the graphite's conductivity. In an oriented piece of graphite, conductivity parallel to these sheets is greater than that perpenicular to these sheets.

The loose coupling among the sheets in graphite contributes to another industrially-important property--graphite powder is used as a dry lubricant.

PHYSICAL CHARACTERISTICS:
Color is black silver. 
Luster is metallic to dull. 
Transparency crystals are opaque 
Crystal System is hexagonal; 6/m 2/m 2/m 
Crystal Habits include massive lamellar veins and earthy masses. also as scaly granules in metamorphic rocks. 
Hardness is 1 - 2 
Specific Gravity is 2.2 (well below average) 
Cleavage is perfect in one direction. 
Fracture is flaky. 
Streak is black gray to brownish gray. 
Associated Minerals include quartz, calcite, micas, iron meteorites and tourmalines. 
Other Characteristics: thin flakes are flexible but inelastic, mineral can leave black marks on hands and paper, weakly conducts electricity. 
Notable Occurrences include New York and Texas, USA; Russia; Mexico; Greenland and India. 
Best Field Indicator is softness, luster, density and streak. 

Graphite is a polymorph of the element carbon. diamond is another polymorph. The two share the same chemistry, carbon, but have very different structures and very different properties.

Diamond is hardest mineral known to man, Graphite is one of the softest. 
Diamond is an excellent electrical insulator, Graphite is a good conductor of electricity. 
Diamond is the ultimate abrasive, Graphite is a very good lubricant. 
Diamond is usually transparent, Graphite is opaque. 
Diamond crystallizes in the Isometric system and graphite crystallizes in the hexagonal system.