Final answer:
Graphite is the 'lead' used in pencils, extracted from carbon ores and mixed with clay. It is known for being soft, allowing it to create marks on paper, which contrasts with the extreme hardness of diamond, another allotrope of carbon.
Step-by-step explanation:
Graphite is the "lead" in the pencil you write with. It is a natural form of carbon that is extracted from ores and not to be confused with actual lead. When mixed with clay as a binder and encased in wood, it forms the familiar pencil lead. This composite material allows artists to create varying line qualities; for instance, a B grade pencil is softer, producing darker lines, whereas an HB or H grade pencil is harder and produces lighter, sharper lines.
The physical properties of graphite are related to its unique structure. Each carbon atom is bonded to three other carbon atoms in a trigonal planar arrangement, forming layers that are kept together by weak forces, allowing them to slide over each other. This slippery quality of graphite lets it rub off onto paper when writing or drawing.
As an element, carbon exhibits varying degrees of hardness depending on its form. Graphite is much softer than diamond, another form of carbon, due to the different atomic arrangements within each allotrope. This softness of graphite is why it is used as pencil lead and not for applications requiring hard materials like glass or diamond.