This is a really nice sample of Ametrine, purple and gold in color, with excellent transparency. Ametrine, also known as trystine or bolivianite, is a naturally occurring variety of quartz. It is a mixture of amethyst and citrine with zones of purple and yellow or orange. Almost all commercially available ametrine is mined only in Bolivia.
The colour of the zones visible within ametrine are due to differing oxidation states of iron within the crystal. The different oxidation states occur due to there being a temperature gradient across the crystal during its formation.