Page 9 - Curriculum Visions Dynamic Book

crystal: a substance that has grown freely so that it can develop external faces. Compare with crystalline, where the atoms are not free to form individual crystals and amorphous where the atoms are arranged irregularly.
electrode: a conductor that forms one terminal of a cell.
mineral: a solid substance made of just one element or chemical compound. Calcite is a mineral because it consists only of calcium carbonate, halite is a mineral because it contains only sodium chloride, quartz is a mineral because it consists of only silicon dioxide.
 This is the structure of graphite. It is made only of carbon minerals and is,
like diamond, an unreactive substance. However, because the structure is in sheets, the bonds between the sheets are relatively weak, so that when pressure is applied, parts of the mineral flake off. This is what allows graphite to be used in pencils.
 The sheen of this piece of graphite is produced by reflection from the sheet-like crystal surfaces.
Graphite
Graphite is a black, soft form of carbon, harder than coal but far softer than diamond. Graphite naturally crumbles to release tiny flakes. This occurs because in graphite the carbon
atoms are arranged in sheets that are poorly linked to each other. As a result, one sheet of crystals readily slides over another.
It is this property that makes graphite useful as a lubricant (it is used to lubricate door locks, for example) and also as a pencil “lead” because it leaves a trail of black flakes as it is moved across paper.
Graphite can also conduct electricity and heat. Graphite makes the central electrode in dry batteries
in many pieces of electrical equipment, such as the brushes in electric motors where sparks occur, as well as in huge steel furnaces.
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