ryod covalent bonding, also has perfect cleavage because it belongs to high symmetry group too.

Although substantially more complex than the simple halides, these sulfates, carbonates and borates are also strongly ionic. They also share highly ordered crystal structures with excellent geometry for cleavage along certain lines. Therefore they too are softer minerals with good cleavage.

Fracture is the resultant break pattern created when a mineral breaks but does not cleave. Glass although not a mineral does fracture when struck, and the pattern is known as uneven or chonchoidal (breaking in shell-like or scalloped edges.) Quartz and glass (SiO2) break in a chonchoidal fashion (as seen to the right), as they has no cleavage. A mineral may fracture as well as cleave, but the fracture pattern will be formed only when it breaks away from its cleavage plane(s). Orthoclase (K Al Si3O8) has both, good cleavage in two directions, but also shows a fracture pattern in the other. Toughness is the ability of a mineral to withstand a sharp blow without fracturing, cleaving or being powdered in the process. Again Diamond is the hardest mineral and cannot be scratched by anything else. If it is hit with a hammer it will turn to dust. It is not tough, it is hard. Jade ( mineral:Nephrite) is one of he toughest minerals, it only has a hardness between 5 and 6, but it can be struck with a hammer and will only deform. It tends to have a fibrous or bladed interlocking structure that makes it tough. The Chinese used dark, non-gem colored jade to make anvils for black-smithing due to its toughness.

Covalent bonding, means that the electron is shared more evenly between the elements. Covalent bonding is much stronger than ionic, and most strongly bonded compounds are not soluble in water or polar solvents. Excellent examples include the Silicon-Oxygen bond and the Aluminum-Oxygen bond. These bonds are very difficult to break and hence most silicates and alumino-silicates tend to be harder and unaffected by water.

ral with very good covalent bonding, also has perfect cleavage because it belongs to high symmetry group too.

ral with very good covalent bonding, also has perfect cleavage because it belongs to high symmetry group too.

The structure of quartz is more like a three dimensional mesh with no obvious planes of weakness. The structure is evenly bonded in all directions and through any angle. Hence there are no obvious cleavage planes. The bonding is more covalent and far less ionic, so it is not affected by water. The surface is thus harder and it can be fractured but not cleaved. There are several different structures for quartz depending on the temperature and pressure under which it was created. Two of the low pressure forms are shown above, and notice the only difference is a slight rotation and orientation of the tetrahedrons with respenct to one another.

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