Agate
Agates are characterized by multiple thin laminations of chalcedony that define distinct banding. many agates are found as amygdales in basalts and other volcanic rocks. Agates can be found in a wide spectrum of colours and can be found South Africa, Namibia, Zimbabwe, Botswana, Swaziland, Mozambique and Lesotho.
Chemical Formular : SiO2 (see chalcedony)
Refractive Index : 1.54
Hardness : 6½ – 7 on the mohs scale
Crystal System : Quartz