Agate (//) is a common rock formation, consisting of chalcedony and quartz as its primary components, consisting of a wide variety of colors. Its IMA symbol is Aga. Agates are primarily formed within volcanic and metamorphic rocks. The ornamental use of agate dates back to Ancient Greece in assorted jewelry and in the seal stones of Greek warriors. Use of beads necklaces with pierced and polished agate goes further back to the 3rd millennium BC in the Indus Valley Civilisation.
|SiO2 silicon dioxide|
|Crystal system||Rhombohedral (microcrystalline)|
|Crystal habit||Cryptocrystalline silica|
|Fracture||Conchoidal with very sharp edges.|
|Mohs scale hardness||6.5–7|
|Birefringence||up to +0.004 (B-G)|