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Ice crystals form snowflakes and are six-sided. Ice crystals form snowflakes and are six-sided. In many solid substances, the atoms or molecules are fixed in place but they are not positioned at random. They are arranged in an orderly or regular pattern known as a crystalline framework or crystal lattice. The result is that the substance forms crystals: orderly, geometric shapes with sharp edges and flat sides at certain angles to each other. These flat sides are called facets. They form shapes such as squares, triangles and rectangles. Many pure metals have a crystalline structure. So do minerals in the rocks, and sugar and salt.

Crystals of quartzCrystals of quartz

Crystal shapes

Crystals are shaped according to the type of atoms and molecules that make up the crystal. There are seven basic shapes, or systems, of crystals. Simplest is the cubic shape which is like a box. Diamonds and common salt (sodium chloride) are cubic crystals. The monoclinic system is like a matchbox which has been squashed slightly flat. The calcium-rich mineral gypsum has this shape. Crystals of quartz in sand grains have a triangular shape. Some natural minerals like ruby and emerald form large, shiny crystals with beautiful colours. They are cut and polished as gemstones.

Bismuth crystalsBismuth crystals
Ruby (red corundum crystals)Ruby (red corundum crystals)


Crystals can be used to convert mechanical energy into electricity. This is called piezoelectricity. Quartz crystals act as kinds of tiny batteries in quartz watches. Piezoelectric crystals are also used in microphones.

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