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<br /> <br /> <br /> <br />19 <br /> <br />Figure 7 - Basalt Flow in Hawaii <br />Clastic sedimentary rocks, such as conglomerate, <br />sandstone, and shale are formed from the fragments <br />of other rocks. Limestone is an example of an organic <br />sedimentary rock. <br />Most people who drive on I-70 near Denver will be <br />familiar with the road cut shown on Figure 8. This cut <br />slope exposes an example of a sequence of <br />sedimentary rock that has been tilted from uplift of the <br />Rocky Mountains. <br /> <br />Figure 8 - I-70 Road Cut in Sedimentary Rock just West of Denver <br />Not all sedimentary rocks are created equal and there <br />are categories of strong rock and weak rock. <br />Throughout the west, many sedimentary rocks were <br />deposited during a time when an inland seaway <br />dominated the area. The rocks deposited in this <br />environment are fine-grained sandstones, limestones, <br />shale, and mudstones. A few examples of these rock <br />types are shown on Figure 9 and Figure 10, <br />respectively. <br /> <br /> <br />Sample of Sandstone Outcrop of Limestone <br />Figure 9 - Examples of Sandstone and Limestone <br /> <br />Thin layers of Shale Blocky Mudstone <br />Figure 10 - Examples of Shale and Mudstone <br />Sedimentary rocks are layered or stratified. The layers, <br />or stratigraphy, are called beds and represent changes <br />in the energy in the depositional environment, <br />sediment particle size, sediment composition, or time <br />between deposition of individual beds. Bedding is the <br />most dominant structural feature in sedimentary rock <br />and often has the most significant impact on the <br />engineering properties of the rock. Bedding planes are <br />often the weakest part of sedimentary rocks since they <br />are breaks in the overall rock mass. The degree of <br />consolidation and cementing of particles impact the <br />nature of sedimentary rocks. Older rocks, buried <br />deeply and subjected to great pressures, will be <br />stronger and more resistant than younger rocks not <br />subjected to those forces. <br />Metamorphic rocks are an assemblage of crystalline <br />minerals, formed when an existing rock, which can be <br />sedimentary, igneous, or even metamorphic, is <br />changed due to heat and pressure. Metamorphic rocks <br />that partially melt often retain minerals and <br />characteristics of the parent rock. During <br />metamorphism, new crystals grow in the orientation of <br />least stress, producing a planar element in the rock <br />called foliation. The three main types of foliation are <br />(a) slately cleavage, (b) schistosity, and (c) gneissic <br />layering or banding as shown on Figure 11. Rocks with <br />only one mineral such as limestone or sandstone do