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11. Speak about the work of a petroleum geologist.
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11. Speak about the work of a petroleum geologist.
LISTENING SCRIPTS
Unit II. Exercise 7. 1
Graphite
Graphite is an allotrope of the chemical element carbon and is denoted by the symbol 'C'. The mineral graphite is steel gray to black in color and is odorless. It is opaque and has a sub-metallic luster. It is known to have a very soft and greasy texture. It can be broken easily and leaves a black streak on the hand when touched. Although graphite is soft and flexible, it is not elastic in nature.
Structure. This element is crystalline in nature; however, perfect crystals of graphite are rarely found. The carbon atoms in its structure are arranged in a hexagonal manner in a planar, condensed ring system. This gives the graphite crystals a hexagonal shape. Different layers of this element are stacked together and held by weak covalent forces to form a giant covalent structure.
Melting Point. Graphite has a high melting point above 3000º F, similar to that of diamond― the other allotrope of carbon. Hence, it is stable over a wide range of temperatures.
Density. As there is a lot of vacant space between the graphite sheets held by the weak covalent bonds, and the density of graphite is 2. 09 to 2. 33 g/cc, which is lower than that of diamond. The measured specific gravity of this element is approximately 2. 26 g/cc. However, it depends upon the purity of graphite. Graphite with a higher ash content shows a specific gravity higher than 2. 26, while its natural form has a lower specific gravity or density due to the trapped porosity.
Solubility. Graphite is insoluble in water as well as other organic solvents. There are no attractive forces that occur between the solvent molecules and the carbons atoms in its structure, and thus, it fails to dissolve in any of the organic solvents.
Electrical Conductivity. There is a vast delocalization of electrons within the carbon layers of graphite. The delocalized electrons are free to move and are able to conduct electricity, thus, making graphite a good conductor of electricity.
Chemical Properties. Graphite is chemically inert to almost all chemicals. It burns completely when heated in oxygen to form carbon dioxide. However, it fails to burn in air, even if it is heated to high temperatures. When heated in the presence of concentrated sulfuric acid and potassium dichromate, graphite gets oxidized to carbon dioxide. Due to its chemical inertness and stability at high temperatures, it is widely used as a refractory material.
(from: http: //www. buzzle. com/articles/graphite-properties. html)
Unit II. Exercise 18
Feldspars
The word feldspar is derived from the word 'Feldspat', of German origin. This word is used to represent a rock which doesn't bear any ore component.
Feldspars are aluminum silicates comprising barium, sodium, calcium, or potassium. The term silicate stands for a combination of silicon and oxygen. This mineral is commonly found in igneous, sedimentary, and metamorphic rocks. It is extracted from large granite formations. In geology, these formations are called plutons. Besides plutons, it is also extracted from sands and pegmatites.
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Feldspar is found in different colors such as white, pink, brown, or gray. This mineral belongs to the tectosilicate group. In case of a pure mineral, each of the crystal has an uneven pattern, and are found grouped together. They are opaque and have a glassy luster.
Some of the rocks are categorized based on the content of feldspar in them. This fact demonstrates the significance of this mineral. The mineral feldspar can be subdivided into different types, depending on the proportion of the elements sodium, calcium, or potassium. The color of the resulting mineral depends on its composition. The higher the sodium content, the lighter the color of the mineral. Alternatively, the higher the calcium content, the more colored the mineral is.
(from: http: //www. buzzle. com/articles/feldspar-types-properties-and-uses. html)
Unit III. Exercise 8
Sedimentary rocks
Sedimentary rocks hold important secrets about Earth's geological and evolutionary history and contain most of the fossil fuel deposits. All these factors make them an important subject of study.
What are Sedimentary Rocks? They are types of rocks, created from deposition of layers upon layers of sediments over time. These types of rocks are formed on the Earth's surface, as well as underwater. Wherever sedimentation goes on, rocks are formed over time. The sediments that compose these rocks may be of organic, chemical, or mineral origin.
Although, these rocks constitute only 5% of the total crust volume, they extensively cover most continental surfaces. They form a thin cover over the whole crust, holding important geological history, locked within them. Most of the natural energy resources like coal and fossil fuels are contained within the layers of this rock type. Drinking water is extracted and minerals are also mined from these rocks, which are created by millions of years of sedimentation.
Types. Depending on the nature of sediments that create them, these rocks can be classified into three prime types:
Clastic: These are composed of broken down fragments of minerals and remnants of weathered rocks. One example of this type is sandstone. They are mostly made up of quartz, amphiboles, feldspar, clay minerals, and other minerals derived from weathering of igneous and metamorphic rocks.
Biochemical: The deposition of the biological remains of various organisms can create certain types of sedimentary rocks. Some examples are limestone (from the deposition of calcium carbonate, containing remains of corals, foraminifera, and mollusks), stromatolites (formed from deposition of microorganism biofilms of blue green algae), oil shale, and coal shale.
Chemical Precipitate: Sediments formed from deposition of chemical reaction precipitates of mineral solutions are called chemical sedimentary rocks. Their formation occurs when water dissolves many minerals and deposits them on evaporation. Examples of this type are gypsum, barite, rock salt, and sylvite.
(from: http: //www. buzzle. com/articles/sedimentary-rock-formation. html)
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