conglomerate
(geology) Cemented, rounded fragments of water-worn rock or pebbles, bound by a siliceous or argillaceous substance.
(organic chemistry) racemate
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(geology) Cemented, rounded fragments of water-worn rock or pebbles, bound by a siliceous or argillaceous substance.
(organic chemistry) racemate
The consolidated equivalent of gravel. Conglomerates are aggregates of more or less rounded particles greater than 0.08 in. (2 mm) in diameter. Frequently they are subdivided on the basis of size of particles into pebble (fine), cobble (medium), and boulder (coarse) conglomerates. The common admixture of sand-sized and gravel-sized particles in the same deposit leads to further subdivisions, into conglomerates (50% or more pebbles), sandy conglomerates (25–50% pebbles), and pebbly or conglomeratic sandstones (less than 25% pebbles). The pebbles of conglomerates are always somewhat rounded, giving evidence of abrasion during transportation; this distinguishes them from some tillites and from breccias, whose particles are sharp and angular.
Conglomerates fall into two general classes: the well-sorted, matrix-poor conglomerates with homogeneous pebble lithology, and the poorly sorted, matrix-rich conglomerates with heterogeneous pebble lithology. The well-sorted class includes quartz-pebble, chert-pebble, and limestone-pebble conglomerates which tend to be distributed in thin, widespread sheets, normally interbedded with well-sorted, quartzose sandstones. The poorly sorted conglomerates include many different types, all related in having very large amounts of sandy or clayey matrix and pebbles of many different rock classes. The graywacke conglomerates are the outstanding representatives. All poorly sorted conglomerates tend to occur in fairly thick sequences, and some of them, typically the fanglomerates (conglomerates formed on alluvial fans) are wedge-shaped accumulations. See also Sedimentary rocks.
Special types of conglomerates, such as volcanic conglomerates and agglomerates and some intraformational conglomerates composed of shale pebbles or deformed limestone pebbles, do not seem to fall easily into either class. See also Breccia; Gravel; Graywacke.
1. A sedimentary rock composed of rounded, water-borne pebbles which have been naturally cemented together. The pudding-stones of the English Chilterns are an example, being formed of flint pebbles cemented with a silica compound.
2. A grouping of industries producing a number of unrelated products.
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Rock consisting of rounded pebbles which are cemented together with a finer material.
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A conglomerate (IPA: /kɒnˈglɒmərət/) is a rock consisting of individual stones that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragements and are thus differentiated from breccias, which consist of angular clasts.[1] Both conglomerates and breccias are characterized by clasts larger than sand (>2 mm).
Paraconglomerates consist of a matrix-supported rock that contains at least 15% sand-sized or smaller grains (<2 mm), the rest being larger grains of varying sizes.[2]
Orthoconglomerates are defined by texture. They are a grain-supported rock that consists primarily of gravel-sized grains (~256 mm), with less than 15% matrix of sand and finer particles.[3]
In rock types such as paraconglomerates and orthoconglomerates, were the matrix to be removed, the rock would collapse. This is because the larger grains are supported by the matrix and, without it, there is nothing to hold the grains together. Therefore, the higher the percentage of matrix, the more unstable the rock.
They differ to breccias in one main way, this is the round edges of the larger sediment/cobbles due to their being deposited in high to very high energy conditions. Possibly from the result of large storm activity when deposition seas allowed sedimentation.
A spectacular example of conglomerate can be seen at Montserrat, near Barcelona. Here erosion has created vertical channels giving the characteristic jagged shapes for which the mountain is named (Monserrat=Jagged Mountain). The rock is strong enough to be used as a building material - see Montserrat abbey front at full resolution for detail of the rock structure.
Another spectacular example of conglomerate, the Crestone Conglomerate may be viewed in and near the town of Crestone, at the foot of the Sangre de Cristo Range in Colorado's San Luis Valley. The Crestone Conglomerate is a metamorphic rock stratum and consists of tiny to quite large rocks that appear to have been tumbled in an ancient river. Some of the rocks have hues of red and green.
Conglomerate may also be seen in the domed hills of Kata Tjuta, in Australia's Northern Territory.
When a series of conglomerates accumulates into an alluvial fan, in rapidly eroding (e.g. desert) environments, the resulting rock unit is often called a fanglomerate. These form the basis of a number of large oil fields, e.g. the Tiffany and Brae fields in the North Sea. These fanglomerates were actually deposited into a deep marine environment but against a rapidly moving fault line, which supplied an intermittent stream of debris into the conglomerate pile. The sediment fans are several kilometers deep at the fault line and the sedimentation moved focus repeatedly, as different sectors of the fault moved]
Metamorphic alteration transforms conglomerate into metaconglomerate.
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