sedimentary
Agate
Silicon dioxide (Chalcedony), SiO2
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, concoidal fracture, specific gravity of 2.60 to 2.65, displays banded or patterned colors including grey, white, yellow, and brown.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, concoidal fracture, specific gravity of 2.60 to 2.65, displays banded or patterned colors including grey, white, yellow, and brown.
Formation & geological history
Forms primarily within the cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions over millions of years.
Uses & applications
Used extensively in jewelry, ornamental carvings, decorative objects, and historically for precision instruments like mortar and pestles due to its hardness.
Geological facts
Agate is one of the most popular stones used in art and lapidary work. The name comes from the Dirillo River (historically called Achates) in Sicily, where agates were found in ancient times.
Field identification & locations
Easily identified by its characteristic concentric banding and waxy luster. Common worldwide, especially in regions with historic volcanic activity like Brazil, Germany, and the US (Lake Superior region).
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