INTRODUCTION ROCK COLOR

Size: px

Start display at page:

Download "INTRODUCTION ROCK COLOR"

Annice Perkins
5 years ago
Views:

1 LAST NAME (ALL IN CAPS): FIRST NAME: 6. IGNEOUS ROCKS Instructions: Some rocks that you would be working with may have sharp edges and corners, therefore, be careful when working with them! When you are done with your lab work, please clean the desk and leave all materials you worked with in the same way you found them! Your work will be graded on the basis of its accuracy, completion, clarity, neatness, legibility, and correct spelling of scientific terms. INTRODUCTION ROCK COLOR: Is an estimate of the % of mafic (dark) minerals by volume. Mafic minerals are dark colored minerals such as olivine, pyroxene, amphibole, and biotite; Felsic minerals are light colored minerals such as quartz, plagioclase feldspar, potassium-feldspar, and muscovite. Black, deep green, deep blue, and deep red colors are considered dark colors; all others are light colors. Ultramafic: > 85% (made up of more than 85% mafic minerals) Mafic (Dark): 46-85% Intermediate: 26-45% Felsic (Light): 0-25% ENVIRONMENT OF IGNEOUS ROCK FORMATION (ORIGIN OF ROCK) Intrusive (plutonic): formed from magma; made up of large minerals (coarse-grained) Extrusive (volcanic): formed from lava; made up of microscopic crystals (fine-grained) TEXTURES OF IGNEOUS ROCKS Coarse-grained (Phaneritic): Coarse grain size; visible grains (1-10 mm); result of slow cooling Very coarse-grained (Pegmatitic): Minerals are exceptionally large: > 1 cm long Porphyritic: Composed of two distinct sizes of crystals. This texture indicates that a body of magma cooled slowly at first (to form the large crystals) and more rapidly later (to form the small crystals, a.k.a. groundmass or matrix). Fine-grained (Aphanitic): Fine grain size (< 1 mm); result of quick cooling Glassy: Lack crystals; superfast cooling Vesicular: Contains tiny holes called vesicles which formed due to gas bubbles in the lava. Very porous; may resemble a sponge. Commonly low density, pumice floats on water. Page 1 of 6

2 Figure 1. Igneous Rock Identification Key QUESTIONS Q1. The rock on the figure below has a porphyritic texture, which means that it contains two sizes of crystals. The large white plagioclase crystals are called phenocrysts and sit in a dark-gray groundmass of more abundant, fine-grained (aphanitic) crystals. Briefly explain how this texture may have formed. Page 2 of 6

Q2. Based on figure 2, name the igneous rock types that form in the given tectonic and geologic environments. Figure 2. Tectonic environments where igneous rocks form.

3 Q2. Based on figure 2, name the igneous rock types that form in the given tectonic and geologic environments. Figure 2. Tectonic environments where igneous rocks form. TECTONIC/GEOLOGIC ENVIRONMENT NAME OF IGNEOUS ROCK FORMED Hot Spot Divergent Plate Boundary Transform Plate Boundary Convergent Plate Boundary Earth s Mantle Q3. Use figure 1, Igneous Rock Identification Key, to answer questions i) to vi). i) A light-colored rock is made up of very large minerals (> 10 mm) and is non-vesicular. This rock is called what? ii) If you had hand specimen of a basalt and a gabbro, what physical differences would you see between the two rocks? Name at least two differences. iii) A felsic (light-colored) rock came from a mixed intrusive and extrusive environments. In addition, this rock shows very coarse-grained minerals (phenocrysts) distributed in mainly coarse grained minerals (groundmass). What name would you give to this rock? Page 3 of 6

4 iv) Name one difference and one common characteristics between scoria and vesicular basalt. Difference: Similarity: v) Write the % of each of the following minerals that you would find in in an average granite. Round your answer to the nearest multiple of 5. Potassium feldspar: % Quartz: % Plagioclase feldspar: % Pyroxene: % Amphibole: % Biotite: % Olivine: % vi) What are two main differences between pumice and obsidian? Q4. Describe the four igneous rocks whose pictures (actual size) are given below. Use, when appropriate, the rock characteristics given below in your description. Explain why you think that rock possesses those characteristics. Rock color: e.g. light, intermediate, or dark Rock texture: e.g. glassy, fine, coarse, very coarse, vesicular Rock environment of formation: e.g. extrusive, intrusive Rock density: e.g. light, heavy Page 4 of 6

5 Scale: mm Scale: mm Page 5 of 6

6 Q5. Obtain 6 igneous rocks from your instructor and for each rock fill in the information required on the Igneous Rocks Worksheet below. Use Figure 1 as needed. SAMPLE # TEXTURES PRESENT (Glassy, Vesicular, Fine-grained, coarsegrained, Very coarse-grained, Porphyritic, etc.) IGNEOUS ROCKS WORKSHEET ENVIRONMENT OF FORMATION (INTRUSIVE OR EXTRUSIVE) ROCK COLOR (FELSIC, INTERMEDIATE, MAFIC OR LIGHT, INTERMEDIATE, DARK) ROCK NAME I-4 I-6 I-7 I-8 (Example) I-13 I-14 Page 6 of 6

6. IGNEOUS ROCKS AND VOLCANIC HAZARDS

LAST NAME (ALL IN CAPS): FIRST NAME: 6. IGNEOUS ROCKS AND VOLCANIC HAZARDS Instructions: Refer to Laboratory 5 in your lab book on pages 129-152 to answer the questions in this work sheet. Your work will