Amethyst or Citrine?

We are often asked about the difference between Amethyst and Citrine, some people claim that Citrine is actually heated Amethyst. For questions of this kind it is never a good idea to rely on random bloggs for an answer. It is always best go back to the chemistry of the mineral in question using a reputable source. The internationally recognised source of reliable information on crystals, minerals, their formation, structure and sources is www.mindat.org This site does not present the views of an individual but Mindat.org is built and maintained by a worldwide community of experts and scientists. Contributors comprise around 450 individuals from around the world who are trusted due to their expert knowledge. Their contributions are also subject to peer review. We know that there are misleading articles on the internet claiming that Citrine is heated Amethyst. However, MIndat says of Citrine it is clear that heated amethyst is not citrine, and also shows no dichroism in polarized light.

What therefore is the difference between the two crystals? First the common factors, both have a Silica Dioxide SiO2  or quartz base. also they both get their colour from the metal impurities contained within the crystal lattice.

Amethyst gains its colour from trace Iron Ferrate FeO4 molecules trapped in the lattice. These molecules are photosensitive with a particular sensitivity to gamma radiation. Over time, they will change from colourless to the familiar pale and deep purple hues which we recognise in the Amethyst crystal.

In Citrine it is the molecules of the metal Aluminum, caught in the crystal’s lattice which produces the smoky, sometimes almost black, colouring of Smoky Quartz. These molecules are heat sensitive between 200 and 300o C. and when subjected to heat,  either naturally in the earth or commercially, will producing the colour in Citrine.  

In chemical and physical terms these two crystals are very different. It is now recognised that the colours in both crystal each have different source. In Amethyst the colour is derived from finely distributed iron minerals, in Citrine it starts with the Aluminum crystals of Smoky Quartz. There is also a difference in the treatment, natural or applied, which produces the different colours and reaction to light; in Amethyst in the form of gamma radiation; in Citrine it is the application of heat.