Agate is a microcrystalline variety of quartz (silica), chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks but can be common in certain metamorphic rocks. Colorful agates and other chalcedonies were obtained over 3,000 years ago from the Achates River, now called Dirillo, in Sicily.The stone was given its name by Theophrastus, a Greek philosopher and naturalist, who discovered the stone along the shore line of the river Achates sometime between the 4th and 3rd centuries BC.
Gomed-Mani belongs to the Navaratna category of the gemstones. It is mostly used to please the shadow planet Rahu. In colloquial terms, it is called Zircon, but it is a misnomer. Even in common English its often referred to as Zircon. But the correct term for it is Hassonite or Agate .This material is sourced from Urday.in
Agate though co-related with Gomed-mani, there is a difference of opinion about the exact identity of Gomed-mani, especially with the indian astrological community. Various descriptions about Gomed-mani (which is considered as a gemstone for the vedic planet Rahu) found across treatise like Ratna Vigyan (Vaidya Balmukund Sharma (Sanskrit)),Rajratna Aushadha Vigyan.(Basant Lal Mukeem),Mani-Mala( S.M. Tagore, (1897)) etc. raise a valid argument towards identity. However since Agate is popularly used it is mentioned here but a further investigation is warranted.