Here's why:

* Atomic Structure: Quartz (SiO2) has a strong covalent bonding structure. This means electrons are tightly bound to the atoms, making it difficult for them to move freely.

* Lack of Free Electrons: Unlike conductors, quartz does not have a significant number of free electrons that can carry an electrical current.

* High Resistance: Quartz has a very high electrical resistance, meaning it strongly resists the flow of electricity.

However, it's important to note:

* Piezoelectricity: Quartz exhibits piezoelectricity, meaning it generates an electrical charge when subjected to mechanical stress (pressure). This property makes it valuable in electronic devices like watches, oscillators, and sensors.

* Conductivity under Extreme Conditions: While normally insulating, quartz can become conductive at extremely high temperatures or under intense electric fields.

In summary, quartz is generally considered an insulator due to its strong covalent bonding and lack of free electrons. However, its piezoelectric properties and potential for conductivity under extreme conditions make it a versatile material with unique applications.