Sedimentary Rock lab 7 - PACE UNIVERSITY – DYSON COLLEGE DEPARTMENT OF CHEMISTRY AND PHYSICAL SCIENCES SCI PDF

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PACE UNIVERSITY – DYSON COLLEGE
DEPARTMENT OF CHEMISTRY AND PHYSICAL SCIENCES

SCI 101: Planet Earth Lecture/ Laboratory Fall, 2020
CRN 2020-70155 August 24 to December 5, 2020
Lecture and Laboratory Sessions: online
Instructor: Dr. Margaret Brewer-LaPorta, Adjunc...

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LAB: _7__: Sedimentary Rock Identification Introduction: Sedimentary rocks are formed from accumulated sediments. Most sedimentary rocks are formed from materials that have been deposited in calm water. Often some characteristics of the sediments are retained in sedimentary rocks. Geologists classify sedimentary rocks into two groups: Clastic (those formed mechanically) and nonclastic (those formed chemically or organically). Objective: All rocks, no matter which type, are identified by texture and composition. Sedimentary rocks are no different. In this lab you will look at the rocks on the PowerPoint and identify their texture and composition. Then with the help of the reference table, use the texture and composition to name the rock. Vocabulary: Please define the following terms. Clastic: a sedimentary rock texture consisting of broken fragments of preexisting rock

Cementation: a type of lithification in which ions in groundwater chemically precipitate to form new crystalline material that sticks sedimentary grains together, cementing the fragments together.

Compaction: a type of lithification in which the weight of overlying material compresses more deeply buried sediment

Fossil: the remains or traces of organisms preserved from the geologic past

Precipitation (from solution): a chemical reaction in which a solid is created from a solution; i.e. minerals dissolved in water will precipitate out of solution and gather at the base of the water solution

Procedure: 1. Look at the sedimentary rock samples on the PowerPoint. 2. On the lab rock chart, write down all the sample numbers. 3. Determine the texture of the rock next. a. Rock has pebbles, sand, silt/clay (mud)….it is clastic. b. Rock has light colored crystals….it is non-clastic. 4. Determine the composition of the rock. a. If the rock is clastic, it typically has quartz (light gray to clear minerals), feldspar (typically pink minerals) and clay minerals (looks like clay). b. If the rock is non-clastic, it typically has halite (tastes salty), calcite (fizzes in acid), or gypsum (scratched with a finger nail). The problem with this is that you can’t taste a picture, fizz a picture, or scratch a picture with a finger nail. So I will drop hints to these on the PowerPoint.

5. Determine the name of the rock by following the ESRT sedimentary rock chart included in your lab folder on Blackboard.

Discussion Questions: (Answer in complete sentences) 1. What is the maximum and minimum dimensions (the size range) for the following particle sizes? a) Cobble: The dimensions of a cobble are between 64mm and 256mm. b) Pebble: The dimensions of a pebble are between 4mm and 64mm. c) Sand: The dimensions of a sand are between 1/16mm and 2mm.

2. How can you distinguish a clastic sedimentary rock from a chemically formed sedimentary rock? A clastic sedimentary rock is made up of pre-existing rocks that have observable pebbles, sand, and silt/clay. The various sediments can be buried, compacted, and cemented together. A nonclastic rock has light colored crystals and is formed from mineral precipitation. A non-clastic rock can taste salty, fizz in acid, or be scratched with a fingernail.

3. Describe the sequence of events in the formation of an evaporite? The chemical process of a rock being formed by an evaporate can occur in shallow basins on land or in the sea. The water in the basin is mineral rich and has a delayed flow or no flow to the sea. First, minerals from the solution precipitate and fall to the bottom of the basin. That solution is then evaporated, and the water is changed from a liquid to a gas. This leaves minerals that crystallize and form new rock. 4. In the space below draw a picture of a pebble of maximum size. Hint: Use a ruler to measure out the maximum size of a pebble (you wrote this down in question 1b), then draw an oval to fit what you measured out. You may need to do this on a separate sheet of paper, take a picture of it, and upload it with your lab. See lab attachments 5. Explain why sedimentary rocks are found covering large areas of the continental igneous rocks.

Sedimentary rocks are found covering large areas of the continental igneous rocks because sedimentary rocks are the result of igneous rocks breaking down. The materials deposited in layers at Earth’s surface (igneous rocks) are what make up sedimentary rocks through temperature and pressure changes.

6. On what bases can sedimentary rocks be identified? Sedimentary rocks can be identified based on their texture and composition. The grain size of a clastic rock can give hints to its composition. A non-clastic rock has light colored crystals and is formed from mineral precipitation. A non-clastic rock’s composition can sometimes be found by performing several tests. Depending on the composition of the rock, it can taste salty, fizz in acid, or be scratched with a fingernail....