You can find Citrine also as a quarz in the  nature, Citrine belongs to the  familiy of Rockcrystal and has the same structure. The rough Citrines we sell are burned Amethystpieces. Because of the heat in the oven (470 °C) the Amethyst changed his color into gold to brown. In nature these Citrines are rare, the pieces which you can buy mostly are burned.  For using as a healing stone there is no difference between natural and burned Citrine.