Agate is formed when silica gel dries and hardens over a long period of time into a form of quartz, coloured by impurities. Agate is usually found in pastel colours but almost any colour or pattern is possible. Patterns include banded agate, moss agate which is white with what looks like a black, brown or green moss growing within it, plume agate which look like it contains plumes of feathers and eye agate which has an eyeball effect.
It was believed to give wearers a bold heart and protect then from dangers. It could cure insomnia and ensure good dreams. In the 19th century eye agate was believed to take on the watchfulness of a guardian spirit and protect the wearer from evil. As such, it commanded very prices.