| Property | Relation to Composition and Crystal Structure |
|---|
| Hardness | Strong chemical bonds result in hard minerals. Covalently bonded minerals are generally harder than ionically bonded minerals. |
| Cleavage | Cleavage is poor if bonds in crystal structure are strong, good if bonds are weak. Covalent bonds generally give poor or no cleavage; ionic bonds are weaker and so give good cleavage. |
| Fracture | Related to distribution of bond strengths across irregular surfaces other than cleavage planes. |
| Luster | Tends to be glassy for ionically bonded crystals, more variable for covalently bonded crystals. |
| Color | Determined by ions and trace elements. Many ionically bonded crystals are colorless. Iron tends to color strongly. |
| Streak | Color of fine mineral powder is more characteristic than that of massive mineral because of uniformly small size of grains. |
| Density | Depends on atomic weight of atoms or ions and their closeness of packing in crystal structure. |
| Crystal habit | Depends on the planes of a mineral’s crystal structure and the typical speed and direction of crystal growth. |