Agate is a type of chalcedony which is a microcrystalline variety of quartz. These minerals have crystals that are too small to be seen with the naked eye.
The formation of agate is incredibly complex and has never been studied in real time. Many questions remain unanswered about the exact process.
Agate can be exceptionally colourful but also commonly occurs in black, white and grey. Colours and patterns come from impurities of other minerals.
Many different types of agate exist. The most popular varieties often have their own name.
Rough and polished agate is popular with rock and mineral collectors around the world. It's also used widely used for its healing properties.