Some healers say that you should never use stones that have been heat treated. I am generally pretty open to using heat-treated stones because I feel like just as crystals have been heated naturally in the earth, when they're heated by man, they have a very similar energy. Now one example of this is Amethyst. Amethyst is often heated by man to form Citrine. And this is often a very deep amber color or brown color. The Citrine that we find in many places is what's mostly commercially available now. And this is just heat-treated Amethyst. Now there is natural Citrine - it's very beautiful. It's sort of closer to a light golden, almost smoky color. And that's fantastic - and I'd always rather use the natural stone that was heated in the earth as opposed to the man-heated stone because I do feel like on a very subtle level, they do differ energetically. But if you don't have access to a naturally heated Citrine, you may want to consider using a man-heated Citrine to get those similar healing qualities. And again, this is going to be a personal preference, what feels intuitively comfortable for you and energetically right for your field. But I do feel like because there's not too much difference in the energy, I'm personally okay with using the heat-treated stones. Other stones that are commonly heat-treated are Aquamarine and blue Topaz. And this is done to actually enhance the blue color of the stone. So whereas the stones maybe partially heated in the earth, and you may have a pale blue color. If they're heated by man, you can have this very intense, deep, bright blue color. So if you are using your stones for chromo therapy or color therapy, you may even want a heat-treated stone, because you'll get that deeper color at a much more affordable price. It's not that you can't find bright, blue stones in Topaz or Aquamarine that have been naturally heated by the earth. But they're very expensive as compared to the paler color or the man-heated stones. So just keep that in mind when you're selecting your crystals.