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The Trouble
With Sedimentary Rocks

     Technically, sedimentary rocks are not more complicated than igneous rocks, or metamorphic rocks for that matter. Yet for the beginner, sedimentary rocks are not as easy to get into as igneous rocks. Take the basic igneous rock classification based on texture and color/composition. It is relatively easy for a beginner to see and understand this system, and it easily leads to interpretations of how igneous rocks form. Simple, neat, and satisfying.
     It is only as one dives more deeply that igneous rocks begin to become more technical and difficult to understand. For example, to really understand how igneous rocks behave one must be able to read and understand phase diagrams.

     Sedimentary rocks, on the other hand, are not easy for a beginner to get into. There are too many exceptions and complications that make sedimentary rock classification and identification a series of, "Yes, but's, . . . " and "Well, there is more to it than that's." Unlike igneous rocks, however, the more you learn about sedimentary rocks the easier they are to understand; the world of sedimentary rocks has a lot of pieces and exceptions, but once we begin to see the patterns they all make simple sense.

Some examples of the problems to be overcome.
     First, unlike igneous rocks where appearance easily leads to classification and interpretation, superficial appearance in sedimentary rocks does not always work well. Two rocks classified the same way may not look all that much alike, and similar looking rocks may not be at all related.

     Second, it is not as easy in sedimentary rocks to identify or estimate the abundance of the components (minerals and rock fragments) that compose the rock, and in anything more than a superficial classification composition is crucial.

     Finally, sedimentary rocks come in such a large variety, and form from such a wide diversity of processes, that it is hard to classify or say anything simply or comprehensively about them and their processes of formation. The exceptions to the "rules" are numerous.

     Thus, even a simple classification of sedimentary rocks is not all that simple, and more useful classifications require facility with ternary diagrams (not that difficult, really).
     We are going to explore several classification schemes here, as well as several systems (keys; see for example) for sedimentary rock identification, from very simple to rather sophisticated. We hope there is something here for everyone's purpose.
     More, we hope that as you learn more you will be encouraged to move to more sophisticated understanding of sedimentary rock depositional environments and evolutionary processes as you learn more about what we can understand about the earth from them.

     This site begins with a simple ideal model, something everyone can quickly understand, that describes the quintessential components of sedimentary rock processes, and their results. Once the simple ideal model is understood all the other sedimentary processes will have a place to fit as we expand each part of the model to greater and greater understanding.

Go to:
   An Introduction to Sedimentary Rocks: The Simple Ideal Model
   Alphabetic Encyclopedia of Sedimentary Rocks
   Strategies Of Sedimentary Rock Classification And Identification
   Return to Home Page

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Last Update: 10/26/00

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