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Besedice Rocks

Sandstone

Sedimentary rocks form only five per cent of the Earth ´s crust, but they cover most ocean floor and three-quarters of its land. Most sedimentary rocks form from particles eroded from the rocks on land. Their main ingredients are rock fragments, quartz, feldspar and clay minerals. These fragments range in size from microscopic grains to boulders. Besides the clastic sedimentary rocks, others, especially carbonates, come from chemical precipitates or the remains of living organisms.Depo­sition lays down sediments in broadly horizontal sheets called beds or strata, each separated from the next in the pile by division called a bedding plane. Beds with ripple reveal ancient currents. Graded bedding with grain size graded vertically may hint at turbidity currents, when sediment rich water sliding soupily down a continental slope. Cross bedding, sand laid down at an angle between two bedding planes, by migrating underwater dunes or ripples. Processes converging sediments to rocks are known as diagenesis. Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. Most sandstone is composed of quartz and or feldspar. Because of the hardness of the individual grains, uniformity of grain size and friability of their structure, some types of sandstone are excellent materials from which to make grindstones, for sharpening blades and polishing of glass and gems. The formation of sandstone involves two principal stages. First, a layer or layers of sand accumulates as the result of sedimentation, either from water (as in a river, lake, or sea) or from air (as in a desert). Finally, once it has accumulated, the sand becomes sandstone when it is compacted by pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains. The most common cementing materials are silica and calcium carbonate.

Interesting shapes are created during weathering

Sandstone detail

Stones of many sizes are in sandstone

GPS position

N 50° 37.938', E 15° 12.296'
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[MAPY.CZ]

Contact

Geopark UNESCO Český ráj
Jiří Vlasák
e-mail:vlasak@geopark-ceskyraj.cz
http://www.geopark-ceskyraj.cz