The largest amethyst deposits on Earth are found in Rio Grande do Sul province in extreme southern Brazil. In this area, numerous mines produce large quantities of amethyst geodes that range in size from a few inches up to tens of feet in height. The amethyst encountered can be very pale purple or can be so dark and gemmy it is gem grade and used in jewelry. The geodes are cut open with large rock saws in Brazil and the edges polished and, in most cases, the outside skin painted a dark green or black to cover up imperfections or cracks that have been sealed with glue. Lower grade amethyst is sometimes put in an oven to turn the amethyst a bright yellow orange citrine color. Any citrine geode you see offered for sale is not true citrine, it is simply low grade amethyst that has been heated.