An important gem mineral with several gem varieties. Qurtz varieties named according to their characteristic colour. Citrine--- yellow
Smoky quarts ---brown
At temperature up to 570c quartz is the stable modification of crystalline silica, SiO2. Quartz occurs in epithermal veins; it is a characteristic mineral of granite and granite pegmatite and is found in sand stones and quartzite.it occurs in hydrothermal metal deposits and in carbonate rocks where it is common. Details of a selection of significant location of ornamental/quality material are given with the type of quartz being discussed.