Common Agate (Sard).
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. Despite their beauty, there are also many agates that are not distinct enough in colour or patterning to be considered a ‘classified’ variety. Common agate is also known as Sard. All agates are composed of SiO2 They form according to a trigonal crystal structure, and have a hardness of 7 on the Mohs scale.