User:Devlin Vong/Agate
Lead section copied from Agate Wikipedia article[edit]
Agate /ˈæɡət/ is a rock consisting primarily of cryptocrystalline silica, chiefly chalcedony, alternating with microgranular quartz. It is characterized by its fineness of grain and variety of color. Although agates may be found in various kinds of host rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks.[1]
Edited paragraphs[edit]
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Agate /ˈæɡət/ is a common rock formation, consisting of silica, chalcedony and quartz as its primary components[2], the formation consists of a wide variety of colours and grain size. Agates are primarily formed within volcanic rocks and metamorphic rocks[1]. These stone have been seen to have dated back as far as Ancient Greece, however with their mediocre durability, their every day uses are most commonly as decorations or jewelry.
Types copied from Agate Wikipedia article[edit]
A Mexican agate, showing only a single eye, has received the name of cyclops agate. Included matter of a green, golden, red, black or other color or combinations embedded in the chalcedony and disposed in filaments and other forms suggestive of vegetable growth, gives rise to dendritic or moss agate. Dendritic agates include fern-like patterns formed due to the presence of manganese and iron oxides. 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 vegetatable material such as a tree limb or root and is called limb cast agate, due to its appearance. Enhydro agate contains tiny inclusions of water, sometimes with air bubbles.
Turritella agate is formed from silicified fossil Elimia tenera (erroneously considered Turritella) shells. E. tenera are spiral freshwater gastropods with elongated, spiral shells composed of many whorls. Similarly, coral, petrified wood and other organic remains or porous rocks can also become agatized.
Coldwater agates, such as the Lake Michigan Cloud Agate, did not form under volcanic processes, but instead formed within the limestone and dolomite strata of marine origin. Like volcanic-origin agates, Coldwater Agates formed from silica gels that lined pockets and seams within the bedrock. These agates are typically less colorful, with banded lines of grey and white chalcedony.
Greek agate is a name given to pale white to tan colored agate found in Sicily, once a Greek colony, back to[clarification needed] 400 BC. The Greeks used it for making jewelry and beads.
Brazilian agate is found as sizable geodes of layered nodules. These occur in brownish tones interlayered with white and gray. Quartz forms within these nodules, creating a striking specimen when cut opposite the layered growth axis. It is often dyed in various colors for ornamental purposes.
Certain stones, when examined in thin sections by transmitted light, show a diffraction spectrum due to the extreme delicacy of the successive bands, whence 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.
Lace agate is a variety that exhibits a lace-like pattern with forms such as eyes, swirls, bands or zigzags (if these[clarification needed] predominate, it is called lattice agate). Crazy lace agate, found in Mexico, is often brightly colored with a complex pattern. Blue lace agate is found in Africa and is especially hard.
Polyhedroid agate is agate which has grown in a flat-sided shape similar to a polyhedron. When sliced, it often shows a characteristic layering of concentric polygons. Polyhedroid agate is thought to be found only in Paraíba State, Brazil. It has been suggested that growth is not crystallographically controlled but is due to the filling-in of spaces between pre-existing crystals which have since dissolved.
Other forms of agate include Holley blue agate (also spelled "Holly blue agate"), a rare dark blue ribbon agate only found near Holley, Oregon; Lake Superior agate; carnelian agate (has reddish hues); Botswana agate; plume agate; condor agate, tube agate (with visible flow channels or pinhole-sized "tubes"); fortification agate (with contrasting concentric banding reminiscent of defensive ditches and walls around ancient forts); Binghamite, a variety found only on the Cuyuna iron range (near Crosby) in Crow Wing County, Minnesota; fire agate (showing an iridescent, internal flash or "fire", the result of a layer of clear agate over a layer of hydrothermally deposited hematite); and Patuxent River stone, a red and yellow form of agate only found in Maryland, where it is the state gem.
Edited paragraphs[edit]
Lace agate is a variety that exhibits a lace-like pattern with forms such as eyes, swirls, bands or zigzags. Blue lace agate is found in Africa and is especially hard[3]. Crazy lace agate, typically found in Mexico, is often brightly colored with a complex pattern, demonstrating randomized distribution of contour lines and circular droplets, scattered throughout the rock. The stone is typically coloured red and white but is also seen to exhibit yellow and grey combinations as well[4].
Moss agate like the name suggest exhibits a moss like pattern and is of a greenish colour. The colouration is not created by any vegetative growth, but rather through the mixture of chalcedony and oxidized iron hornblende. Dendritic agates also displays vegetative features, including fern-like patterns formed due to the presence of manganese and iron oxides[5].
Turritella agate (Elimia tenera) is form from the shells of fossilized freshwater Turritellas, gastropods with elongated spiral shells. Similarly, coral, petrified wood, porous rocks and other organic remains can also form agate[6].
Coldwater agates, such as the Lake Michigan Cloud Agate, did not form under volcanic processes, but instead formed within the limestone and dolomite strata of marine origin. Like volcanic-origin agates, Coldwater Agates formed from silica gels that lined pockets and seams within the bedrock. These agates are typically less colorful, with banded lines of grey and white chalcedony[7].
Greek agate is a name given to pale white to tan colored agate found in Sicily, once a Greek colony, back to[clarification needed] 400 BC. The Greeks used it for making jewelry and beads.
Brazilian agate is found as sizable geodes of layered nodules. These occur in brownish tones inter-layered with white and gray. Quartz forms within these nodules, creating a striking specimen when cut opposite the layered growth axis. It is often dyed in various colors for ornamental purposes.
Polyhedroid agate forms in a flat-sided shape similar to a polyhedron, when sliced, it often shows a characteristic layering of concentric polygons. It has been suggested that growth is not crystallographically controlled but is due to the filling-in of spaces between pre-existing crystals which have since dissolved.
Other forms of agate include Holley blue agate (also spelled "Holly blue agate"), a rare dark blue ribbon agate only found near Holley, Oregon; Lake Superior agate; Carnelian agate (has reddish hues); Botswana agate; Plume agate; Condor agate; Tube agate containing visible flow channels or pinhole-sized "tubes"; Fortification agate with contrasting concentric banding reminiscent of defensive ditches and walls around ancient forts; Binghamite, a variety found only on the Cuyuna iron range (near Crosby) in Crow Wing County, Minnesota; Fire agate showing an iridescent, internal flash or "fire", the result of a layer of clear agate over a layer of hydrothermally deposited hematite; Patuxent River stone, a red and yellow form of agate only found in Maryland; Enhydro agate contains tiny inclusions of water, sometimes with air bubbles.
Bibliography[edit]
- ^ a b Donald W. Hyndman, David D. Alt (2002). Roadside Geology of Oregon (18th ed.). Missoula, Montana: Mountain Press Publishing Company. p. 286. ISBN 978-0-87842-063-6.
- ^ Wang, Yifeng; Merino, Enrique (1990-06-01). "Self-organizational origin of agates: Banding, fiber twisting, composition, and dynamic crystallization model". Geochimica et Cosmochimica Acta. 54 (6): 1627–1638. doi:10.1016/0016-7037(90)90396-3. ISSN 0016-7037.
- ^ Simmons, Robert; Ahsian, Naisha (2007). The Book of Stones: Who They Are and What They Teach. North Atlantic Books. ISBN 978-1-55643-668-0.
- ^ Atkinson, Bill; Ackerman, Diane (2004). Within the Stone: Photography. BrownTrout Publishers. ISBN 978-0-7631-8189-5.
- ^ Schumann, Walter (2009). Gemstones of the World. Sterling Publishing Company, Inc. ISBN 978-1-4027-6829-3.
- ^ Grant, Ember (2016-06-08). The Second Book of Crystal Spells: More Magical Uses for Stones, Crystals, Minerals... and Even Salt. Llewellyn Worldwide. ISBN 978-0-7387-4844-3.
- ^ Garvin, Paul (2010-09-13). Iowa's Minerals: Their Occurrence, Origins, Industries, and Lore. University of Iowa Press. ISBN 978-1-60938-014-4.