Half and Half
Ametrine is a fine marriage of citrine with amethyst. Composed of silicon dioxide (SiO2), ametrine is a naturally occurring variety of quartz characterised by noticeable split between purple and yellow (or orange) colour sections in the stone. Ametrine owes this particular quality to differing oxidation states of iron within the crystal: oxidised segments would turn into citrine, unoxidised into amethyst. The entire process is caused by temperature gradients developing during formation of the crystal.