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A few words about Ooids and Oolites OOIDS are a distinctive type of sand that usually form on the sea floor. Where ooids grow through physical accretion, they tend to have thin concentric layers analogous to tiny tree rings, except they are spherical instead of cylindrical. In contrast, ooids that grow by chemical precipitation are more likely to have radiating sprays of crystals arranged like the spokes in a bicycle wheel; but many ooids grow via a combination of these two processes and show both concentric and radial structures internally. www.sculptureconservation.com /oolites.html   (613 words)

USC Sequence Stratigraphy Web However, some recent ooids from the Great Salt Lake of Utah and the Persian Gulf in the vicinity of Qatar have a radial fabric of needles. Ooids with asymmetric coatings and superficial oolites form in quiet water. Occasionally broken radial ooids may act as the nuclei for other ooids suggesting that the radial fabric is developed during deposition. strata.geol.sc.edu /thinsections/caco3-ooids.html   (202 words)

CEREBROID OOIDS IN THE MIDDLE JURASSIC ROCKS OF SOUTHERN MONTENEGRO The cerebroid ooid diameter ranges from 0.4 to 1 mm but most of the ooids are from 0.6 to 0.8 mm diameter with an average size of 0.68 mm. Nuclei of the cerebroid ooids are made of preexisting radial concentric and tangential/micritic concentric ooids, skeletal grains, and micrite/peloid cryptocrystalline calcite. Five types of cerebroid ooids were recognized: 1) Cerebroid ooids with a radial concentric inner cortex; 2) Cerebroid ooids with a tangential/micritic concentric inner cortex 3) Cerebroid ooids with a large palisade cortex growing from the skeletal nucleus 4) Superficial cerebroid ooids with a composite nucleus; and 5) Globular cerebroid ooids with no recognizable nucleus. gsa.confex.com /gsa/2006AM/finalprogram/abstract_112978.htm   (480 words)

Photomicrographs of nonskeletal grains The sample shows a range of ooids, from those with a small nucleus and thick cortex(the oolitic coating), to those with a large nucleus and a single oolitic lamina. The matrix between the ooids is a mixture of carbonate mud and sparry calcite cement. This latter feature is unlikely to occur in ooids, where precipitated carbonate laminae are formed while the grain is held in suspension. plaza.snu.ac.kr /%7Elee2602/atlas2/nonsk.html   (507 words)

GFF-online presents: Tidal facies in the Upper Silurian Öved-Ramsåsa Group of Scania, Sweden: Linkages of radial and ... Of particular interest are the presence of radial and cerebroid ooids and evaporite tracers. The radial fabric of the ooids is regarded as primary and it is suggested that these ooids formed in suspension, in the low-energy subtidal lagoonal environment. Implications for a restriction in water circulation and progressive evaporation, coinciding with the ooid formation are seen in associated sediments of this facies. www.gff-online.se /site/article.asp?articleID=906   (270 words)

A Tropical Island Story The ooid is formed chemically in warm agitated shallow water by bacteria and algae precipitating aragonite (a form of calcium carbonate). ooid banding and the outer band appears even darker: blue plastic is clearer and lighter: central nucleus less distinct: interior banding less distinct with less clear past signs of initial spalling. Ooid outer banding can be determined as freshly deposited micritic cement: ooid interior more distinct and center ooid interior banding clearly showing past signs of initial spalling. www.nhm.ac.uk /hosted_sites/quekett/island.html   (485 words)

Laboratory cultures of calcifying biomicrospheres generate ooids - A contribution to the origin of oolites Carbonate precipitate; cyanobacteria; diatoms; ooids; spherulites; microbial association. However, ooids would often be washed out of stromatolitic microbial mats and deposited elsewhere. The formation of a typical ooid is connected with a nucleation center, which can be of biotic or abiotic origin (Kühl et alii, 2003). paleopolis.rediris.es /cg/CG2004_L03/index.html   (2490 words)

Modern iron ooids from a shallow-marine volcanic setting; Mahengetang, Indonesia -- Heikoop et al. 24 (8): 759 -- ... Ooids are composed of concentric accretionary layers of limonite admixed with amorphous silica, precipitated around andesitic rock fragments. Ooid formation is likely promoted by precipitation of iron and silica from exhalative fluids rising up through the substrate. Concentric layering is thought to result from constant agitation of ooids associated with currents and expulsion of gas from the sediment. geology.geoscienceworld.org /cgi/content/abstract/24/8/759   (285 words)

INFLUENCE OF PRIMARY OOID MINERALOGY ON POROSITY EVOLUTION, UPPER JURASSIC SMACKOVER FORMATION, EASTERN GULF COAST ...   (Site not responding. Last check: ) Ooids in the Smackover Formation at Womack Hill field, southwestern Alabama, have tangential, radial, and mixed tangential and radial fabrics. Based on well established petrographic criteria, tangential ooids were originally aragonite, radial ooids were originally magnesian calcite, and mixed tangential and radial ooids were originally bimineralic (aragonite and magnesian calcite). Magnesian calcite ooids were neomorphosed to calcite, and present porosity in these rocks is interparticle and solution-enlarged interparticle. gsa.confex.com /gsa/2004AM/finalprogram/abstract_79779.htm   (384 words)

Description of Carbonate Rocks Ooids are carbonate grains which are usually small less than 1 mm in diameter spherical grains which posses a series of concentric laminations when view in cross section. In the pure sense of folk's classification all four rocks could exists however in practice since one is forced to attributes all microcrystalline to cryptocrystalline calcite grains under 2 mm in diameter to the pellets or pelloids the terms intrasparite and intramicrite are not used. Furthermore an oomicrite is itself a rare rock type as the process that cause the formation of ooids generally excludes the formation of a lime mud or microcrystalline to cryptocrystalline calcite matrix. people.uncw.edu /dockal/gly312/carbonate/carbonate.htm   (2193 words)

Bryan Kinney's hardground page   (Site not responding. Last check: ) Ooids are coating the exterior of the rock. Ooids and bivalve fragments indicate the depositional environment as shallow marine, in or just under the wave base, and in the photic zone. The photo here shows an ooid with other smaller ooids surrounding the large one. www.wooster.edu /geology/hdgd/Bryan.html   (218 words)

[Coral-List] Lower Keys ooids I am a little suspicious that they may not be true ooids, at least in the Bahamian sense. So for unknown reasons ooid sands were forming during the Pleistocene, (when sea level was 20 feet higher than today) and creating the tidal sand bars that became the lower Florida Keys of today. Ooids also formed and created beaches that are now 300 ft below present sea level off the keys. coral.aoml.noaa.gov /pipermail/coral-list/2006-May/003214.html   (359 words)

[Coral-List] Lower Keys ooids Of course I have no idea if the sand is composed of true ooids or Halimeda sands, but it will be interesting to find out. So for unknown > reasons ooid sands > were forming during the Pleistocene, (when sea > level was 20 feet > higher than today) and creating the tidal sand bars > that became the > lower Florida Keys of today. Ooids also formed and > created beaches > that are now 300 ft below present sea level off the > keys. coral.aoml.noaa.gov /pipermail/coral-list/2006-May/003215.html   (479 words)

Splendor in Stone - Tour - OOLITIC SANDSTONE This sandstone is built from quartz grains (yellow, white, gray) and calcareous grains (dark) held together by a calcite cement. The calcareous grains that contain a distinctive internal structure are ooids. Ooids form as spheres, but some get broken or deformed when compacted in a sandstone. www.nysm.nysed.gov /virtual/collections/splendor_in_stone/splendortour17.html   (135 words)

Geology Field Trip -Osmington Oolite, Dorset, England - Corallian Strata Ooids are present not only in the Osmington Oolite but also in overlying limestones. Associated with the ooids is a fibrous carbonate. The fibrous carbonate is probably an isopachous (equal thickness), fibrous fringe cement around the ooids, of the type described by Chowdhury (1982a) and Sun (1990) from the Osmington Oolite. www.soton.ac.uk /~imw/osoolit.htm   (2368 words)

SME--VIRTUAL ATLAS OF OPAQUE AND ORE MINERALS The central ooid has a nucleus of banded haematite (white-grey, higher reflectance) which may be a fragment of an earlier ooid. Ooids with a central nucleus of chamosite (dark grey) have concentric outer bands of haematite (white, highest reflectance) where the individual haematite crystals lie tangentially. Slight differences in reflectance (centre) are due to variations in the grain size of the haematite between the bands, or to the ratios of haematite, limonite and silicates within the bands. www.smenet.org /opaque-ore/Plate48.htm   (483 words)

IngentaConnect Detrital ooids of Holocene age in glaciomarine Champlain Sea sedi...   (Site not responding. Last check: ) Detrital ooids, from 0.1 to 0.5 mm diameter, almost completely dominate two 0.3 m thick layers between one and two metres depth at a site in clay-size-rich, isostatically uplifted, glaciomarine, Champlain Sea sediments north of Gatineau, Quebec. The ooids, composed of layers of tangentially oriented, platy particles, are physical aggregations of glacially ground, rock flour with the identical mineral suite that constitutes the regional Champlain Sea sediments. A hydrodynamic "hail-stone" model, which requires a somewhat turbulent sedimentary environment within the water column, probably created by wind–wave action that kept ooid nuclei in suspension while the flocculating effect of brackish to marine conditions induced particle accretion onto their surface, is proposed for their formation. www.ingentaconnect.com /content/nrc/cjes/2004/00000041/00000006/art00010   (321 words)

Amazon.com: "ferruginous ooids": Key Phrase page Ooidal ironstones These are characterized by the presence, or former presence, of ferruginous ooids or pisoids. This horizon is composed of greyish to yellowish sandy marls, with glauconite and ferruginous ooids, phosphatized fossils and large gastropods. Formation of'the heavy ferruginous ooids is difficult to explain by an analogy to the "repeated suspension in carbonate cloud" that applies to aragonite ooids. amazon.com /phrase/ferruginous-ooids   (332 words)

Institute F.-A. Forel   (Site not responding. Last check: ) Previous investigations in the western portion of Lake Geneva, Switzerland, have shown that shallow water sediments are mainly composed of ooids. The device was set at 2.50 meter water depth containing 12 glass slides arranged at 90° on a horizontal plastic arm in order to avoid particle setting on their surfaces. SEM observations of these frosted glass slides showed that, as in the natural ooids, low-Mg calcite precipitates are always found in close association with microbial biofilms. www.unige.ch /forel/staff/plee.html   (449 words)

Ooids - Article from FactBug.org - the fast Wikipedia mirror site In geology, ooids are a type of sand grains that usually form on the sea floor. Similar to a snowball which accumlates more snow as it rolls down a hill, ooids form by growing larger and accreting material as they move around. Kidney stones are a type of ooid, as they are rich in calcium and possess similar growth structures. www.factbug.org /cgi-bin/a.cgi?a=462931   (163 words)

Ooid Ooids with radial crystals (such as the aragonitic ooids in the Great Salt Lake (Utah, USA) grow by ions extending the lattices of the radial crystals. There are several factors that affect ooid growth: supersaturation of the water with respect to calcium carbonate, the availability of nuclei, agitation of the ooids, a constant location, water depth and the role of microbial organisms. Kidney stones are similar to ooids in their layered structure; they are sometimes rich in calcium (calcium oxalate) or phosphate (struvite). www.omniknow.com /common/wiki.php?in=en&term=Ooids   (1697 words)

IngentaConnect Depositional environments and iron ooid formation in condensed se...   (Site not responding. Last check: ) Iron ooids are found from the shoreface to the offshore zone. The contemporaneous, thick, predominantly marl sections that occur laterally are devoid of iron ooids and were deposited in deeper settings (distal offshore zone). Three distinctive nanostructures are identified in the cortex laminae: (i) a nanograined crystalline structure typical of primary goethite; (ii) a secondary nanoflaked structure thought to have formed mechanically by reorientation of the goethite crystals; and (iii) a coalesced structure acquired by subsequent diagenetic recrystallization. www.ingentaconnect.com /content/bsc/sed/2005/00000052/00000005/art00004   (311 words)

PYRITE OOIDS AS A RELIC FEATURE OF INTERMITTENT SEA LEVEL DROP AND SHALLOW WATER CONDITIONS IN DEVONIAN BLACK SHALES   (Site not responding. Last check: ) Pyrite ooid beds occur above erosion surfaces that were most likely produced by a lowering of sea level, and have been interpreted as sequence boundaries because of their large lateral extent. Realization that these pyrite ooid beds represent replacement of pre-existing beds of chamositic iron ooids, suggests an oxygenated water column at the time of their formation and wave interaction with seafloor sediments. Further careful conodont dating of proximal chamositic ooid beds and distal pyrite ooid occurrences may help to confirm eustatic origin for other shallowing episodes in the Devonian inland sea, and help to isolate eustatic shallowing events from those forced by local tectonics and sedimentation. gsa.confex.com /gsa/2002AM/finalprogram/abstract_40221.htm   (460 words)

Amazon.com: "berthierine ooids": Key Phrase page Two ooids show partially replaced echinoderm frag- ments at nuclei. the ooids or they may have formed around berthierine flakes or fragments of broken ooid. One of the features of berthierine ooids that distinguishes them from the more familiar aragonite -calcite ooids is the evidence that they were soft at the time... amazon.com /phrase/berthierine-ooids   (216 words)

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