Lab 5

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Rowan University *

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06103

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Geology

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Dec 6, 2023

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Lab 5 Sedimentary Rocks and Processes CE 342 – Geology Dr. John Schuring – Spring 2023 1) What is stratification, and why do all sedimentary rocks exhibit it? Stratification is a process in which the layering in most sedimentary rocks and igneous rocks are formed on the surface of the Earth, from where lava flows and volcanic fragmental deposits. All sedimentary rocks form a layer of sediment deposited in basins then later transfer into stratification. 2) Explain the process of diagenesis. What are the most common cementing agents that bond the clasts together in sedimentary rocks? Diagenesis describes the process of physical and chemical changes in sediment. First causing water to rock interactions, microbial activity, and compaction. After sedimentation, calcite (calcium carbonate) silica and hematite (red iron oxide) most common are the cement. 3) Sandstone is a relatively common rock, but the clasts within this rock may vary. Name the three most common variations of sandstone, and what kind of clast(s) does each contain? ● Quartz wackes - This type is dominated by sand. It is composed of more than 90% of quartz. ● Arkose - Consists of more than 25% of feldspar. ● Lithic wacke - It is also dominated by sand but is composed of more than 10% of rock fragments and more than 15% of silt and clay. 4) What sedimentary rocks will react to dilute hydrochloric acid? Indicate whether or not the rock surface needs to be powdered. The sedimentary rock which reacts with dilute hydrochloric acid is Limestone. As carbonate minerals react with these acids, being a carbonate rock limestone also reacts with HCl. The reaction can be written as- CaCO3 + 2HCl = CO2 + H2O + Ca++ + 2Cl This is an effervescence reaction. Reacting with the limestone carbon dioxide generates bubbles on the surface of the limestone. If the limestone is composed of calcite mineral then the rock surface reacts with the acid vigorously, and if the limestone is composed of dolomite then the powdered surface will react sluggishly.
5) Basalt and black limestone have very similar appearance with regard to color and texture. Name two simple physical tests that may be used to distinguish between the two. On rocks, the acid test can be performed with a drop of hydrochloric acid on limestone, which is almost entirely made up of calcite, and produces a powerful fizz. Basalt has a black or grayish-black appearance. The presence of calcium carbonate in limestone will cause the rock to fizz during an acid test. If nothing changed during your test, it's sure that either the liquid was too acidic or you didn't have limestone. Basalt is made up primarily of olivine, pyroxene, and plagioclase, and is high in iron and magnesium. They can also be porphyritic. So, basalt can have a coarsely porous texture because of holes caused by gas bubbles. 6) What is the mineralogy of chert? In which kind of rock beds does chert form, and what are some typical shapes of the deposits. Chert is a fine-grained, hard sedimentary rock made up of quartz micro-crystals (SiO2). It usually appears as nodules, stratified deposits, or concretionary masses. Chert is made up of sediments that covers most of the deep ocean floor. Cherts, on the other hand, range in purity from over 99% silica to impure nodular cherts with less than 65% silica. Chert is widely used as construction material for road paving. The waxy shine, a conchoidal (shell-shaped) fracture of the silica mineral, a hardness of seven on the Mohs scale, and a smooth (non-clastic) sedimentary texture are all distinguishing traits. 7) Briefly explain how the alkali-silica reaction causes serious deterioration in Portland cement concrete structures. What specific rock can trigger the reaction? This reaction occurs when the reaction occurs there is a formation of gel on the surface of aggregate particles. This gel destroys the bond between cement and aggregate by exerting internal pressure. Ultimately the expansion occurs which leads to formation of cracks in cement paste. The alkali-silica reaction occurs mainly between the hydroxide ions of the dissolved salts of sodium and potassium and the silica molecules of siliceous rocks such as opal and chert. 8) Clastic sedimentary rocks are mainly deposited within water environments. Order the following rocks according to the velocity of water where they are formed, from highest to lowest velocity: siltstone, shale, breccia, sandstone. Name the principle that controls the sorting process? From highest velocity to lowest velocity Breccia -> Sandstone -> Siltstone -> Shale
Because breccia is coarse grain sediments which consists of boulder size fragments while sandstone consists of the sand size particles. Silt size particles are deposited thereafter, Shale which is fine grain sediments are deposited. If the different sizes of the particles are present then it is poor sorting. If the same size of the particles are present then the sediments are good sorting. Sorting depends on the mode of transport, roundness of the particles. 9) Sedimentary Structures: Draw a sketch (by hand or CAD) illustrating each of the sedimentary structure listed below. Label the various parts of each structure, as appropriate. A. Bedding (flat) B. Cross-bedding C. Mud Cracks 10) 15-Specimen Collection: Examine the identified sedimentary rock collection provided. Fill in the information in the table below. Compare the specimens with the figure provided by the instructor and the information in the Lab Notes. Specimen No. Rock Name Texture (Clastic, Non-clastic Chemical, Non-clastic Organic) Grain Size (if clastic) Matrix and/or Cementing Agent Acid Reaction (test carbonates only) 1 Conglomerate Clastic Coarse Sand Silica Iron oxide no 2 Arkose Clastic Silt - Coarse Sand silica calcite yes 3 Sandstone Clastic Medium Sand silica Clay no 4 (Quartz) Sandstone Clastic Medium Sand Silica Clay no
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