The most popularly used agate used in jewelry-making are: Red agate, black agate or black onyx, carnelian or chalcedony, and Botswana agate.
Visit this link to learn more about how agate is formed and their properties.
Structure and Availability
It’s a form of chalcedony.
It’s composed of Silicon Dioxide and ranges from 6-7 hardness on the Moh’s scale.
Its origin is in its name, Botswana, Africa.