To make it harder. Pure graphite would be too soft for use as a writing pencil.
Graphite is the main ore of pencil lead.
At the moment you can obtain 3 different varieties: the traditional one (graphite refill encapsulated inside a wooden wrapper of cedar), the propelling pencil (pens with very fine refills of graphite) or the bar pencil (Similar to the propelling pencils but with thicker and more resistant graphite bars. Approx.. 5-9 mm in diameter).
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Graphite is a gray carbon based substance used in pencil lead. Graphite has a lattice like structure and is arranged in layers so as to be easily rubbed apart unlike diamond which is a more interlocking structure of pure carbon and is extremely hard and unmalleble.
Clay mixed with blood of the gods.
Graphite mixed with clay is used to create graphite pencils. The clay helps to bind the graphite together, giving the pencil its structure and allowing for smooth and consistent writing or drawing. Different ratios of graphite to clay determine the hardness or softness of the pencil lead.
Graphite.
Graphite is used as a lubricant and, mixed with clay, in pencil lead.
Pencil "lead" is actually made of graphite, which is a form of carbon. The graphite is mixed with clay to give it form and strength. These mixture of graphite and clay are then encased in wood to create a pencil.
Pencil Tip is made of Lead, but nowadays it is usually made of Graphite.
The "lead" of a pencil is made from graphite, which is a form of carbon.
Graphite is the mineral that is used to make the lead in a pencil. Despite its name, pencil "lead" is actually composed of graphite mixed with clay.
Graphite, a form of carbon
The formula for pencil lead is a combination of graphite mixed with clay. The most common type contains graphite and clay in a ratio of approximately 80:20. The clay acts as a binder to hold the graphite together and determine the hardness of the lead.
The core of a pencil is typically made of graphite mixed with clay. Graphite is a crystalline form of carbon, while clay is a mineral composed of finely-grained particles of hydrous aluminum silicates.
The grey or black core of a pencil is made of graphite which is a form (known as an allotrope) of the element carbon. To vary the hardness of the 'lead' in the pencil the graphite may be mixed with clay or some other substances.
The mineral is graphite.