Agate is the name given to a family of chemically related stones. There are over thirty distinct varieties of agate making it one of the largest families of stones. All agates are composed of SiO2 They form according to a trigonal crystal structure, and have a hardness of 7 on the Mohs scale. *Please see other gem varieties of Agate such as Carnelian and Bloodstone in their own listing. Click on each product to read more about their healing properties.