Crystals

Many substances occur naturally as crystals. Here the yellow crystals of sulfur contrast with the shiny white aggregations of cal-cite (calcium carbonate).

Most simple chemical compounds consist of crystals. These cannot always be seen clearly because they are often grouped together in a mass that has no particular shape. But if a lump of crystalline material is examined closely, tiny individual crystals can be seen.

All crystals have a definite geometric shape, determined by the way in which the atoms of the substance are linked together. For example, in a crystal of common salt (sodium chloride) the atoms of sodium and chlorine are arranged so that they lie at the corners of a series of (imaginary) cubes; the result is a Cubic crystal.

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