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Two allotropes of carbon have crystalline structures: diamond and graphite.In a crystalline material, atoms are arranged in a neat orderly pattern.Carbon allotropes that lack crystalline structure are amorphous, or without crystalline shape.The allotropes of carbon have very different chemical and physical properties. Graphite does not melt when heated, but sublimes at about 3,650°C (6.600°F).For example, diamond is the hardest natural substance known. The Mohs scale is a way of expressing the hardness of a material. The melting point of diamond is about 3,700°C (6,700°F) and its boiling point is about 4,200°C (7,600°F). On the other hand, graphite is a very soft material. Sublimination is the process by which a solid changes directly to a gas when heated, without first changing to a liquid.Its density is about 1.5 to 1.8 grams per cubic centimeter.The main difference among these materials, he said, was the presence of a "black combustible material" that he knew was present in charcoal.Carbon was officially classified as an element near the end of the eighteenth century.

The name they used, carbone, is based on the earlier Latin term for charcoal, charbon. Allotropes are forms of an element with different physical and chemical properties.

The numerical value for these properties varies depending on where the graphite originates.

The amorphous forms of carbon, like other non-crystalline materials, do not have clear-cut melting and boiling points.

Their densities vary depending on where they originate. The combustion (burning) of coal gave rise to the Industrial Revolution (1700-1900).

Another highly important and very unusual property of carbon is its ability to form long chains.

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