The agate crystal is a microcrystalline-quartz mineraloid that has a lustrous display of multi-color banding and results from long-term accumulations of siliceous groundwater deposits in rock cavities. Much like other mineraloids, all agate types form over thousands of years inside the existing voids of other igneous, sedimentary, and metamorphic rocks that contain silica-rich groundwater. And color formations and patterns can vary depending on numerous environmental factors. In fact, the layering and banding typically visible within an agate gemstone is representative of the shapes of the voids from which it develops. Agate is a popular and highly marketable stone amongst gem enthusiasts worldwide. This is mostly due to its colorful displays, mystifying geological origins, and its spiritual and cultural affiliations.