Smoky quartz

Description

This α [quartz](http://webmineral.com/data/Quartz.shtml) (SiO₂) crystal is an example of 'smoky quartz'. Smoky quartz typically owes its colour properties to some minor contamination by Al₂O₃. While the mechanism of this contamination is not entirely understood, we know it usually happens due to radiation damage, since it is commonly found in pegmatites that are high in thorium, postassium and uranium. The crystal is 35 millimetres in length.