Ametrine, also known as Trystine, or by its trade name as 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.
Legend has it that ametrine was first introduced to Europe by a conquistador's gifts to the Spanish Queen, after he received a mine in Bolivia as a dowry when he married a princess from the native Ayoreos tribe.