Question about the chemical bonding in Quartz?

Question

I am confused! Some text books state that Quartz is 100% covalently bonded;others state it is combination of ionic and covalent bonds. My understanding is it should be purely covalent as we are talking about Si-O bonds (both non metals, Ionic bonds involve metals and non metals). If Quartz is partly covalent and ionic then why does it display this behavour?
ANy help would be appreciated. Also is it true the impurites in quartz are only very small (such as Ti, Fe, or Al) and as such don't alter its chemical compostion?

Answer 1

First of all no bonding is purely ionic or covalent. They are extreme theoretical standpoints. All forms of chemical bonding are made up of a mixture of the two in different proportions.

Although covalent bonding dominates in quartz, ionic character is present thenks to which Si-O bonds can give up electrons and quartz can function as a semiconductor.

Impurities in small amounts do not alter the chemical nature significantly but they have a great effect on the physical traits such as colour or electrical conductivity.