Agate is a term applied not to a distinct mineral species, but to an aggregate of various forms of silica. It usually forms in concentric layers in a wide variety of colors and textures. The most common colors are white to grey, light blue, orange to red and black. Agate is often found as a round nodule, with concentric bands like the rings of a tree trunk. The first archeological findings of different implements made of agate date back to 8000 years ago.
There exist various types of agate.
A Mexican agate, showing only a single eye, has received the name of "Cyclops agate." Dendrite agates have beautiful fern like patterns on them formed due to the presence of manganese and iron ions. Other types of included matter deposited during agate-building include sagenitic growths (radial mineral crystals) and chunks of entrapped detritus (such as sand, ash, or mud). Occasionally agate fills a void left by decomposed vegetative material such as a tree limb or root and is called limb cast agate due to its appearance. Turritella agate is formed from fossil Turritella shells silicified in a chalcedony base. Similarly, coral, petrified wood and other organic remains or porous rocks can also become agatized. Agatized coral is often referred to as Petoskey agate or stone.
Certain stones, when examined in thin sections by transmitted light, show a diffraction spectrum due, hence they are termed rainbow agates. Often agate coexists with layers or masses of opal, jasper or crystalline quartz due to ambient variations during the formation process.
Other forms of agate include carnelian agate (usually exhibiting reddish hues), Botswana agate, blue lace agate, plume agate (such as Carey, Graveyard Point, Sage, St. Johns, Teeter Ranch and others), tube agate (with visible flow channels), fortification agate (which exhibit little or no layered structure), fire agate (which seems glow internally like an opal) and Mexican crazy-lace agate (which exhibits an often brightly colored, complex banded pattern).
Agate was highly valued as a talisman or amulet in
ancient times. It was said to quench thirst and protect from fevers. Persian magicians used agate to divert storms. Agate bowls were popular in the Byzantine Empire. Collecting agate bowls became common among European royalty during the Renaissance and many museums in Europe, including the Louvre, have spectacular examples.
History: The mining of agate in the Nahe River valley in Germany which was already documented in 1497 gave rise to the cutting center of Idar-Oberstein, Germany. Originally, the river was used to power the grinding wheels. When the Nahe agate deposit was exhausted in the nineteenth century, Idar cutters started to develop the agate deposits of Brazil, which also sparked exploration and discovery of Brazil's rich deposits of other gemstones.
reade more...
There exist various types of agate.
A Mexican agate, showing only a single eye, has received the name of "Cyclops agate." Dendrite agates have beautiful fern like patterns on them formed due to the presence of manganese and iron ions. Other types of included matter deposited during agate-building include sagenitic growths (radial mineral crystals) and chunks of entrapped detritus (such as sand, ash, or mud). Occasionally agate fills a void left by decomposed vegetative material such as a tree limb or root and is called limb cast agate due to its appearance. Turritella agate is formed from fossil Turritella shells silicified in a chalcedony base. Similarly, coral, petrified wood and other organic remains or porous rocks can also become agatized. Agatized coral is often referred to as Petoskey agate or stone.Certain stones, when examined in thin sections by transmitted light, show a diffraction spectrum due, hence they are termed rainbow agates. Often agate coexists with layers or masses of opal, jasper or crystalline quartz due to ambient variations during the formation process.
Other forms of agate include carnelian agate (usually exhibiting reddish hues), Botswana agate, blue lace agate, plume agate (such as Carey, Graveyard Point, Sage, St. Johns, Teeter Ranch and others), tube agate (with visible flow channels), fortification agate (which exhibit little or no layered structure), fire agate (which seems glow internally like an opal) and Mexican crazy-lace agate (which exhibits an often brightly colored, complex banded pattern).
Agate was highly valued as a talisman or amulet in
ancient times. It was said to quench thirst and protect from fevers. Persian magicians used agate to divert storms. Agate bowls were popular in the Byzantine Empire. Collecting agate bowls became common among European royalty during the Renaissance and many museums in Europe, including the Louvre, have spectacular examples.History: The mining of agate in the Nahe River valley in Germany which was already documented in 1497 gave rise to the cutting center of Idar-Oberstein, Germany. Originally, the river was used to power the grinding wheels. When the Nahe agate deposit was exhausted in the nineteenth century, Idar cutters started to develop the agate deposits of Brazil, which also sparked exploration and discovery of Brazil's rich deposits of other gemstones.
