Question

Lab Exercise Lab Exercise: Identification of Metamorphic Rocks la this laboratory exercise, you will identify the most common metamorphic rocks based on their texture and composition. Feel free to download the Metamorphic Rocks Photo Guide from the online supplement to help you make your identification. Instructions Step 1: Retrieve the bag labeled Lab #8 Metamorphic Rock Samples from your lab kit. and place the specimens (numbered 18 through 25) on a white sheet of paper. Step 2: Determine the identity of each rock, then write its name in the proper cell of Figure 8.13. The flow chart in Figure 8.14 will help you to first determination to make is whether a sample is foliated or nonfoliated Remember that some nonfoliated rocks occasionally show signs of banding. If you suspect a rock is not really foliated, follow up by looking for other properties, by identifying component minerals, and by conducting other tests, as necessary. If you decide to conduct an acid test, rinse the sample in water and dry it first so that you don't get a false positive result from dust in the bag that may have settled on the sample. row down the possibilities. The er Identification Sample # Gneiss Schpet Slate Slate Marble Quartzrte Hornfals Anthrneite coal # 18 # 19 # 20 # 21 #22 #23 # 24 # 25 Figure 8.13 Metamorphic Rock Identification Chart. 183 Lesson 8/Metamorphism and Metamorphic Rocks d. Short Answer 1 What is metamorphism? MetamorphisM the change of Mnerals geologre texture the profolrth melting n xtng rocks, withat How is foliation different than sedimentary layering? pArd Magma Folratron s MetamorphisM. Sedrment lay ering de position. Ts 3 What properties of slate make it good roofing material? Slate is extremely fine grmed, whreh Makes,t relatryely iMpervious to wtter, one reason 4. What is a metamorphic grade? What metamorphic grades are associated with the four main categories of foliated rocks? 5. What history does the presence of most metamorphic rocks reveal? 6. What does the presence of hornfels reveal? Hornfels fine gran, dark color, an d baked otppearance recognzable by TS 189 Lesson 8/Meta morphism and Metamorphic Rocks

Answer 1

1. Ans. Metamorphism. The word metamorphism means change form. In geology this refers to the change in mineral assemblage and texture that results from subjecting a rock to conditions such as pressure, temperature and chemical environments different from those under which the rock originally formed.

2.ans. Foliation is formed when pressure is exerted on rocks and the minerals are compressen and they align themselves perpendicular to the direction of applied pressure giving rise to flaky minerals. It happens due to metamorphism. Foliation generally results due to dynamothermal metamorphism in coarse-grained igneous rocks like granites and sandstones(sedimentary) and metamorphic rocks like schists.

In sedimentary there are visible bedding planes in sedimentary layering. These are called planes of weakness - the bedding planes separate the beds from each other. The thickness of each layer in sedimentary formation may show variation: from few centimeters to many meters.

3.ans.Slate is a fine grained metamorphic rock and is impervios in nature . Another reason it is high grade metamorphic rock an is resistant to weathering and also breaks in plane sheets which make it more convinent for roofing material.

4.ans. It is the general term for describing the relative pressure-temperature condition under which metamorphic rocks form. Three terms are used to express the grades:

1. Low Grade. It prevails within a temperature range of 200⁰-400⁰C

2. Medium Grade. This grade prevails up to a temperature range of 650⁰C

3. High Grade. It is believed to begin at temperature range of 580⁰ C under pressure of 3.5 kb and continues upto temperature of 800⁰ C.