Agate is a variety of chalcedony, which is a cryptocrystalline form of silica, comprising very fine intergrowths of both quartz and moganite. Its unique banded appearance results from microscopic quartz crystals forming in layers, with each layer often varying in color due to impurities or changes in the conditions during its formation.
Agate forms in volcanic and metamorphic rocks. It often fills cavities in these rocks, like those found in lava flows or geodes, where the mineral-rich water deposits silica in the voids over time. The banding in agate can be caused by changes in the chemistry of the fluid, rate of cooling, or variations in the deposition environment.
The term "agate" derives from the Greek name for the river Achates in Sicily, now called the Dirillo, where agates were first discovered. Agate has been used since ancient times, with artifacts dating back to the Bronze Age. It was particularly popular in the Victorian era for jewelry and decorative items due to its durability and the beauty of its patterns.
Agate has been used for:
Notable locations for agate include:
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