Why are most quartz crystals not colorless (clear)?

Explained

Explanation:

Quartz is never found in pure form, most of the quartz crystal have some or other form of impurity in them. It is these impurities that impart color to the quartz crystal. Ions of different elements like magnesium, iron, aluminium are amalgamated with in the SiO₂ crystal imparting it different colors. The Piezoelectric properties of Quartz are also because of the same reason

( availability of free electron).

radiative zone

explanation    

radiative zone is the layer of the sun which energy is transferred away from the core by radiation. although, the core is the only part of the sun that produces an appreciable amount of heat through fusion. in fact, 99% of the energy produced by the sun takes place within 24% of the sun's radius.