Citrine is a rare crystal that ranges in color from pale yellow to a yellow-olive. Its name comes from ‘citron,’ the French word for ‘yellow.’ Citrine is a type of quartz and also often occurs with smokey quartz; smoky citrine and citrine with smoky phantoms are naturally occurring. Natural citrine gets its color from hydrous iron oxide and is one of the few naturally occurring yellow crystals. After amethyst, citrine is one of the most popular crystals in the world.
Ametrine is a different, relatively new discovery, found in the Anahi Mine in Bolivia. Ametrine is essentially part citrine and part amethyst, hence the portmanteau. Ametrine is formed due to a partial-heat exposure to the amethyst that creates the yellow color, and, because of this, ametrine does not have the iron inclusion of natural citrine. I went to a gem show and found someone selling Bolivian Ametrine from that very mine and he confirmed that the crystal is formed naturally through heat that occurs under ground. For ametrine I advise using the metaphysical properties of amethyst with a yellow boost.
You can’t talk about citrine without discussing heat treated amethyst. It’s such a pet peeve of mine that my friend regularly holds it up in crystal shops and waits for me to roll my eyes. It bothers me because the properties of amethyst and citrine are not similar, let alone interchangeable. That means when you accidentally use heat treated amethyst in the place of citrine, you think you’re working with citrine, and you’re not. Additionally, the healing properties of amethyst are compromised by the treatment process. The process is so simple that you can do it in your home oven, though I do not recommend it at all. Here you can see my photo, taken last December, showing a natural citrine point (top/right) in comparison to a heat treated amethyst cluster being sold as citrine (bottom/left). Fake citrine is one of my crystal pet peeves, maybe my top crystal peeve.
Real citrine is much more expensive than fake citrine, so keep that in mind when you’re shopping. Also, real citrine never appears in that dark, amber color, or on a matrix similar to amethyst. Fake citrine tumble stones are incredibly common; they are a combination of white and this honey amber color always. Hibiscus Moon has a great post about this issue and goes into the science of how it works, so if you’re interested in learning more, check out her article here.