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The Best Mineral Crystals

Minerals are made of atoms and rocks are made of minerals. Minerals can grow into crystals if they have the room to grow. New mineral crystals develop in two ways. Some minerals result from molten rock. Beneath the earth's surface molten rock is called magma. Above the surface, it is called lava. When the liquid rock cools, atoms form mineral crystals. Another way minerals form is when water evaporates and leaves behind the atoms of dissolved elements. These atoms bond together and form solid minerals. There are four categories of crystals: covalent, metallic, ionic and molecular.

Covalent Crystals
- Diamonds are covalent crystals.
  
  Covalent crystals result from the atoms in the crystal sharing electrons. This makes the crystal a large molecule. This type of crystal has a high melting point. Diamond and zinc sulfide crystals are typical covalent crystals.
Metallic Crystals
- Copper wire conducts electricity.
  
  In metallic crystals, the metallic atoms are latticed, and the outer electrons of the atoms float free around the lattice. These are dense crystals with high melting points. Examples are nickel and copper. Because of the gas of electrons free-floating, these make good conductors of electricity.
Ionic Crystals
- Table salt is an edible crystal.
  
  Ionic crystals have atoms bonded by electrostatic forces. Another phrase for electrostatic forces is ionic bonds, which gives this crystal type its name. Ionic crystals are hard and have high melting points. A prime example is table salt (NaCl).
Molecular Crystals
- Table sugar has a low melting point.
  
  Molecular crystals have a molecular structure held together by non-covalent interactions. These are soft crystals with low melting points. Table sugar is an example.

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