Water also carries dissolved minerals, such as silica and cations downstream as well as in the groundwater. Boulders and smaller rock fragments continue to be broken up and chemically altered as they tumble downstream. Water carries or rolls particles in rivers, from the smallest suspended clay particles to the largest boulders. The most important transporting agent is water. Quartz is itself an agent of mechanical weathering in the form of blowing dessert sand.Īs the process of weathering proceeds the products are carried off. Not only is quartz the most stable of the common rock forming minerals in chemical weathering, its high hardness and lack of cleavage make it quite resistant to mechanical weathering. Rock fragments will also remain where the rocks are not completely weathered. Some of the dissolved CO 2 reacts with the water forming the chemical compound carbonic acid.Ĭomplete weathering of silicate rocks will yield:Ģ) quartz sand (if the rock originally contained quartz) Most natural surface waters are slightly acidic because carbon dioxide from the air dissolves in the water. Hydrolysis is the reaction of minerals in weakly acidic waters. Others, especially silicate minerals, are altered by a chemical process called hydrolysis. Some minerals like halite and calcite may dissolve completely. In chemical weathering minerals are changed into new minerals and mineral byproducts. Mechanical weathering breaks rocks into smaller and smaller pieces but without otherwise altering the minerals. In mechanical weathering rocks are broken up into smaller pieces by frost-wedging (the freezing and thawing of water inside cracks in the rock), root-wedging (tree and other plant roots growing into cracks), and abrasion caused by, for example, sand-blasting of a cliff face by blowing sands in the dessert, or the scouring of water transported sand, gravel, and boulders on the bedrock of a mountain stream. When rocks (igneous, sedimentary, or metamorphic) are at or near the surface of the earth they are exposed to the processes of weathering. The latter two steps are called lithification. Sedimentary rocks are the product of 1) weathering of preexisting rocks, 2) transport of the weathering products, 3) deposition of the material, followed by 4) compaction, and 5) cementation of the sediment to form a rock. In that case, sedimentary rocks are derived rocks because they are formed from fragments of pre-existing rocks. And in the darkness between the stars, an old enemy lurks, fearless, perhaps waiting for order to collapse entirely.Igneous rocks are sometimes considered primary rocks because they crystallize from a liquid. The mercenaries they hire for a few credits a kill are too few, too unreliable to do so either. The Cooperative's police force, concentrated near a few influential planets, can no longer maintain order. The trade ships that once safely travelled between planets now have to be well armed and escorted to fend off pirate attacks, from small-time criminals desperate for their next meal, to powerful robber barons extracting tithes from everyone who passes through their space. The two thousand star systems of the Cooperative once enjoyed a golden age of peace and prosperity, and perhaps the wealthiest of them can still pretend to. Perhaps one day, everyone might know your name. You've got a ship, some weapons, and enough spare cash to get started - and one day, you might get the fame, wealth or glory you want. Among the seven trillion people who are - at least officially - Cooperative citizens, you are nobody.
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