How to tell the difference between heat treated and natural Citrine. Left column: Natural Citrine and Right column: Fake Citrine, Heat treated or baked Amethyst
Natural Citrine is pretty dull and smoky with a slight honey color to them, quite like Smoky Quartz but with a slightly more golden tone to it.
Natural Citrine will also often have smaller points attached to the larger one and usually but not always have hematite around the base where it was once attached onto it’s matrix.
Baked Amethyst will often be bright orange to almost a burned dark orange. You will either find this ‘Citrine’ to appear broken as before it was baked it was apart of a larger cluster of Amethyst. And most Citrine geodes are just baked Amethyst geodes.
The very last photo on the right column is of the same Geode Cathedral, only one side had gone through the heat treatment.
The heat it takes to turn the color of the Amethyst varies upon how light or dark you want it to end up. (I beg you guys to PLEASE don’t go shoving your Amethyst points/clusters into your ovens. Don’t do it. Don’t even think about it.) It takes about 900°F (482°C) to change the Amethyst to Citrine, and it takes an even hotter 1022-1040°F (550-560°C) to make the Amethyst turn the dark yellow or golden brown-ish red of most Citrine Geodes that you see. (Once again. Don’t shove your crystals in your oven. Don’t do it.)
Sources: http://www.secretcrystals.net, http://stacierocks.blogspot.com, http://hibiscusmooncrystalacademy.com, https://www.etsy.com/shop/SpiritCarrier, https://www.etsy.com/shop/PureSpiritCrystals, http://www.the-vug.com, http://urbanmogullife.com, http://www.flickr.com/photos/cobalt/, http://www.majestic-quartz.com