1. Mineral Properties Each and every mineral has certain mineral properties. The properties of each mineral depends on the following;  1) The type of elements present (i.e. composition) 2) The arrangement of atoms (i.e. structure) 3) The strength of bonding (i.e. ionic, molecular, or metallic) Reference: Tarbuck and Lutgens Pages 39 - 44

2. Diamond Versus Graphite Some minerals can have the same chemical composition, but have different physical properties. For example, the hardness and cleavage of diamond and graphite differ despite the fact that both are made from carbon atoms (C) only.  Diamond Graphite

3. Hardness and Cleavage Diamond and Graphite are forms of pure carbon; however, the physical properties (hardness and cleavage) are quite different for the two minerals.  Different physical properties are due to:  1) Different atomic structure of the carbon atoms. 2) Strength of bonding between carbon atoms differs for the two minerals.

4. Diamond  Diamond consist of a tetrahedral network of carbon atoms. Most stable atomic structure.  Strength of bonding between carbon atoms are strong in all directions. No weak areas of bonding.  Strong bonding and tetrahedral atomic arrangement allows diamond to be the hardest mineral (10) with no apparent cleavage planes. Note that diamonds are found in kimberlite, which is an igneous rock that was pushed upwards from deep within Earth. At such depths, the pressure is great enough to arrange the carbon atoms very tightly together.

5. Graphite  Weak bonding between the layers and a layered atomic arrangement causes graphite to be a soft mineral (1 to 2) with basal cleavage (i.e. one cleavage plane). It is dark grey to black in colour.  Strength of bonding between carbon atoms within the layers are strong; however, strength of bonding between the layers is weak. Weak Bonding Strong Bonding  Graphite consist of carbon atoms arranged in sheets (or layers). Sheets

6. Sample Problem Diamond and graphite have identical chemical composition (both are composed of carbon). Explain why the cleavage of these two minerals is different. Answer: Cleavage is the ability of a mineral to break along planes of weak chemical bonding. The strength of the bonds between carbon atoms in graphite planes are weaker than they are in diamond. Carbon atoms in graphite are arranged in a different structural pattern than diamond (sheets as opposed to macromolecule, tetrahedral).