Gemstones: Ametrine

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.

Bolivianite

Another name for ametrine, bolivianite refers to the main existing source of the natural stone currently on the world’s market, which is the Anahí mine in eastern Bolivia. According to the legends, the Bolivian mine was a part of the dowry received in the seventeenth century by a Spanish conquistador upon marrying a local princess from the Ayoreos tribe. Through that marriage, ametrine found its way into the royal courts of Europe.

1960s Comeback

This South American mine later fell into oblivion only to be rediscovered after three hundred years, in the 1960s. Soon, ametrine made its commercial comeback, gaining relative popularity among gem dealers and jewellery designers.

Polished ametrine (bolivianite).
Polished ametrine (bolivianite).

The Bigger, the Better

Fine ametrine displays clear contrast between two colours, ranging from vivid to strong for purple and medium dark to moderately saturated for orange. The most sought-after stones are those above 5 carats, since larger gems usually exhibit the most intensely saturated hues.

Cutting Techniques

The cutting techniques for ametrine tend to focus on showcasing the bi-colour properties of the stone, with the most popular being the rectangular step- and brilliant cut. Ametrine is also popular in free-form or fantasy cuts.

Synthesising Ametrine

The existing laboratory techniques allow to produce synthetic ametrines in two ways: either by differential heat treatment of amethyst, or through beta irradiation of natural citrine. Available on the market yellow-blue and yellow-green synthetic ametrines do not occur naturally.