Amethyst is a type of Quartz. It colour comes from iron and manganese compounds infiltrating the quartz.
Forms mostly as stubby pyramid like crystals although sometimes form in long Prismatic crystals (rare).
Amethyst also forms the lining of geodes.
Amethyst turns to Citrine under heat and pressure.
Chemical Formula - SiO2 (silicon dioxide)
Mohs Hardness – 7