lab 6

GEOL 1302 Lab 06 Chemical Sedimentary Rocks In this lab, you are going to describe and identify some common chemical sedimentary rocks. Your lab instructor will summarize the main characteristics of the different rocks. In the second part of the lab, you should list some possible environments in which the rocks that you identified might have formed. Some help to perform the rock identification and information about chemical sedimentary rocks can be found below. Please submit your worksheets to your instructor. Important notice: In this lab you will be using hydrochloric acid (HCl). This is a dangerous liquid for skin and eyes, and it can also damage clothes. – By starting to work on this lab, you acknowledge that you have read and understood the dangers associated with the use of HCl. If you don’t want to use it, ask your lab instructor to use it for you. Composition: ● Which minerals can you identify (e.g. gypsum, calcite, …) ● Organic material Texture and Other Properties: ● Layering ● Reaction with HCl ● Color ● Fossils/fossil fragments present ● Fine vs. coarse grains Type: ● Biochemical vs. chemical Identification and Formation: http://geology.about.com/od/rocks/a/Rock-Tables.htm http://ratw.asu.edu/aboutrocks_chemicalsedimentary.html http://www.earthsci.org/education/teacher/basicgeol/sed/sed.html 1

tzoparia newton Examining and Classifying Chemical Sedimentary Rocks Sample Number Composition Texture and Other Properties Type Rock Name 1 it is composed of halite and sodium chloride could be a colorless, grayish color, usually coarse grained chemical Rock Salt 2 decayed vegetation/ organisms organic coarse grained chemical peat 3 the tiny shells of marine animals and remains of marine type algae can be a white or light gray in color porous soft Fizzed with HCI biological chalk 4 calcium carbonate abundance of fossils Fizzed with HCI porous coarse grained biological Fossiliferous Limestone 5 silicon dioxide fine grained no fizzing with acid biological chert 6 fossils fizzed with HCI has many shapes and fossils, contains many holes chemical Travertine 7 calcium sulfate dihydrate Crystals are vitreous (glassy like), (massive) form is dull fine grained biological Rock Gypsum 2

Chemical Sedimentary Rock Formation tzoparia newton How and in what environment might the rocks that you identified in the first part of the lab have formed? Sample #/Rock Name Formation/Environment Rock Salt rock salt usually forms in large bodies of salty sea/lake water, usually in a Arid climate. peat mostly favored in humid and warm conditions, can also form in colder areas chalk a form of limestone, usually forms from a fine grained marine sediment. can form in deep marine environments and/or empiric seas on continental crust, or on continental shelving during the high sea periods. Fossiliferous Limestone can form in warm, shallow clear waters. chert form in carbonate rocks can form in the deep depositional environments Travertine can usually form in and around mineral spings like at the national hot springs Rock Gypsum mostly form in thick layers/beds in lagoons where waters are high in calcium and sulfate 4