Amethyst is a popular stone, one of very few naturally occurring fully purple gems. It is the traditional birthstone for February. Amethyst is a variant of quartz. Iron impurities give it those beautiful shades of purple. Regarding its famous color-if you run across prasiolite, sometimes called green amethyst, just be aware that it’s most likely heat treated or irradiated. (It’s not an issue, so long as you know and aren’t being told or charged for the natural gem. They are a lovely mint green, it’s just that the natural stone is extremely rare.)
Geodes are partially filled hollow cavities in rock that are lined by minerals. Their name comes from the Greek for earthlike. (As in Gaia.)
One example of a geode would be a gas bubble in lava. That hollow stays and over time solutions containing dissolved minerals can filter in and leave deposits within the hollow, often resulting in layers of agate and then layers of quartz and/or calcite crystals.
Studying the order of the layers can give a window into the geologic history of the area in which the geode is found.
I like working with slices of geodes because you get to see that external skin and the swirls of agate layers as well as the sparkling crystals.