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All atoms have a strong tendency to achieve a stable configuration of the outer electron shell in which all possible electron sites are filled. This is why bonding takes place. This means that the forces that bond cyrstals together are electrical in nature.

The type and intensity of bonding are responsible for the physical and chemical properties of minerals. Hardness, cleavage, fusibility (to become liquid or plastic), electrical and thermal conductivity, and thermal expansion are directly related to bonding forces. In general, the stronger the bond the harder the crystal, the higher its melting point, and the smaller its thermal expansion. Diamond is so hard because of the very strong electrical forces linking its carbon atoms.

Molecular:

Recognizable molecules in the structure and the crystal are held together by non-covalent interactions like van der Waals forces or hydrogen bonding. The van der Waals' weak bond ties neutral molecules into a lattice and is the weakest of the chemical bonds. This type of bond is not often found in minerals.

Van der Waals'-bonded minerals are characterized by:

An example is the mineral graphite, which consists of covalent bonded sheets of carbon atoms linked only by van der Waals' bonds. This is what gives graphite a slippery feel.

Metallic:

In metallic bonding the electons are very weakly tied into the metal structure. An electron owes no allegiance to any particular nucleus and is free to drift through the structure.

Metallic-bonded minerals are characterized by:

Among minerals, only the native metals display pure metallic bonding.

Ionic:

In ionic bonding the ions are joined together in the cyrstal structure by the attraction of their unlike electrostatic charges. One ion has a negative charge, the other a positive charge.

Ionic-bonded minerals are characterized by:

• Moderate hardness and specific gravity
• Fairly high melting and boiling points
• Very poor conductors of electricity and heat

• Insolubility
• Great stability
• Very high melting and boiling points

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