Ch-5-Lab-7

Sedimentary Rocks (Lab 7) For this lab you will need:  Rock and Minerals Quick Study Guide  Mineral and Rock Identification Chart (in Canvas)  Rock and Mineral Set  Hand lens  White distilled vinegar In this lab you will identify 6 sedimentary rocks. To do so, you will observe various properties of sedimentary rocks such as type, grain size/composition, sorting, rounding, and cement type. Read through the introductory material discussing these properties below and using the Rock and Minerals Quick Study Guide and the Classification of Sedimentary Rocks Table in the Minerals and Rocks Description Guide to complete the Sedimentary Rocks Identification sheet for each sample. Introduction to Sedimentary Rocks Sedimentary rocks cover most of the Earth’s surface and provide a thin covering over older igneous and metamorphic rocks. Sedimentary rocks are useful and important for geologists because they can tell us about ancient environments, the location of the continents in the past, the location of ancient mountain ranges and ancient oceans, and ancient climates and climate change. Many geologists study sedimentary rocks because some sedimentary rocks contain valuable natural resources such as petroleum and coal. A sedimentary rock is consolidated sediment held together by the process of lithification. Lithification is the process by which unconsolidated sediment is compacted and cemented together. Cement is a mineral or chemical that is precipitated in the pore spaces of the grains and binds them together. Pore spaces are the voids in-between the grains. Some common examples of cement are quartz, calcite, and iron oxide. Calcite cements will fizz with acid while iron oxide cements will have a rust color and stain the rocks. There are varying degrees of cementation. A well-cemented sedimentary rock is considered indurate . In poorly cemented sedimentary rock, individual grains will easily be broken apart or crumbled. Geologists use the term friable to describe poorly cemented sedimentary rocks. There are three types of sedimentary rocks: clastic, chemical, and organic. Clastic sedimentary rocks consist mostly of pieces of preexisting rocks, usually minerals and/or rock fragments. Chemical sedimentary rocks consist mostly of mineral crystals precipitated from solutions. Common minerals would be gypsum, halite, calcite, and microcrystalline quartz. Microcrystalline quartz is chert. Organic sedimentary rocks consist mostly of the remains of organisms, such as plants and animals. Plant fragments make peat and coal. Fragments of shells and coral have skeletons made of calcite that form skeletal limestone. Complete the Sedimentary Rock Identification sheet for each sample then answer the supplemental questions below. Begin by choosing the type of sedimentary rock best describing each sample. Then use the Rock and Minerals Quick Study Guide and the Classification of Sedimentary Rocks Table in the Minerals and Rocks Description Guide to identify the name of the sample. If you identify a sample as clastic, then identify the grains that compose the rock. If it is chemical/biochemical/organic, then

identify the major minerals or materials that comprise the sample. Continue filling in each column. Identify the cement as calcite, iron oxide, quartz, or none. Identify the sorting and rounding as discussed in the previous lab. Record any other notable features, especially ones that will help you identify these samples on the lab exam. The 6 sedimentary rocks in today’s lab are: Conglomerate Limestone Quartz Sandstone Banded Sandstone Black Shale Oil Shale To test whether a rock fizzes (effervesces) with acid you can put a single drop (A SINGLE DROP) of distilled vinegar on the rock’s surface and watch for small bubbles. You may need to use your hand lens to get a better view. Vinegar is a very weak acid and will not fizz very aggressively. You should still be able to see a few bubbles if a rock effervesces under the presence of an acid.