As we mentioned above, Chalcedony stone is a type of microcrystalline quartz. You must be thinking, what does it mean? Well, different categories of quartz stones can either be microcrystalline (with microscopic crystals that are densely compacted together) or macrocrystalline (with large crystals that are visible). An example of macrocrystalline quartz is Citrine or amethyst.