Most of the amethyst and citrine geodes available today come from Brazil. The process for geode formation and mineral crystallization can take over 130 million years! With amethyst and citrine geodes, transparent crystals of macrocrystalline quartz can vary in color depending on the exact level of iron content. In specimens which form with lesser iron content, crystals will lend a violet to purple color (amethyst geode); and geodes which form with higher iron composition will result in the attractive golden 'citrine' color.
When it comes to citrine and amethyst geodes, citrine is generally considered the rarer of two. Some (not all), amethyst geodes can be heated to produce golden citrine colors, but heated citrine geodes tend to exhibit more reddish tones than unheated citrine geode specimens.
When it comes to buying citrine and amethyst geodes, personal preferences are usually the main factors, but there are also a few other guidelines and 'points' to take into consideration. As with all colored gemstones, color is usually the most important criteria when it comes to value, but even so, many buyers actually prefer lighter violets over deep purples, or refreshing lemony-yellow color versus a deep Madeira orange. Besides color, the size and shine of the geode's crystal points are both important factors to consider. Points can range in size from extra small to extra large, and for most collectors, somewhere in between is most preferable. Geodes with medium-sized points and uniform arranged crystals tend to increase value, even though both large and small points are still very much in high demand.
Geodes with smooth and well shaped crystals are valued for their ability to reflect more light. Amethyst and citrine geodes with banded line formations are also highly valued. The line formations are typically the result of the layered formation of agate, a type of chalcedony quartz. Geodes can be found in a variety of interesting shapes; some of the most popular geode shapes include rounded, cylindrical and 'cathedral' or church-steeple shaped nodules. When it comes to geode shape, preference comes into play. Tall and deep geodes pieces are popular for pendants, while shorter, rounded geodes may be better suited for other types of jewelry or ornamental design. Lastly, geodes are commonly found with other mineral inclusions. Unlike most colored gemstones, inclusions are usually welcomed. Inclusions of calcite or fluorite can make for very interesting crystals, especially for those looking for unique pieces to add to their collection!