Common Rocks (Chapter 2)

Transcription

1 GEOLOGY 306 Laboratory Instructor: TERRY J. BOROUGHS NAME: Common Rocks (Chapter 2) For this assignment you will require: a streak plate, glass plate, magnet, dilute hydrochloric (HCl) acid, microscope, and various mineral samples (all provided by instructor). Objectives for chapter 2: you should be able to recognize, name, and describe individual minerals within rocks; be able to examine a rock and determine if it is an igneous, sedimentary, or metamorphic rock; list and define the terms used to describe the textures of igneous, sedimentary, and metamorphic rocks; use a classification key to identify a rock; recognize and name some of the common rocks by sight. IGNEOUS ROCK TERMS: TEXTURAL TERMS: Pegmatitic : very coarse-grained, larger than your thumb (> 1-inch) Phaneritic : coarse-grained, easily seen, uniform size Aphanitic : fine-grained, uniform size Porphyritic : phenocrysts in a finer grained matrix Glassy : similar to glass Frothy : glassy & vesicular, many small vesicles, foamy-looking Vesicular or Cellular : many visible vesicles Fragmental/Pyroclastic : particles, ash, fragments of rock, etc. fused together Please note! If a sample has a porphyritic texture, the term porphyritic is added to the rock name. (i.e., PORPHYRITIC GRANITE, PORPHYRITIC BASALT, PORPHYRITIC RHYOLITE.) COMPOSITIONAL TERMS: FELSIC : light colored INTERMEDIATE : medium shades MAFIC : dark colored ULTRAMAFIC : rare (composition of the mantle) SEDIMENTARY ROCK TERMS: GRAIN SIZE FINE-GRAINED: MEDIUM-GRAINED: COARSE-GRAINED: You will not be able to see individual grains. Mudstone (shale) belongs in this group. You will be able to see individual grains. Sandstone belongs in this category. Grains are larger than 2 mm. Conglomerates and breccias belong in this group. CLASSIFICATION (ORIGIN AND RESULTING TEXTURES) INORGANIC DETRITAL / CLASTIC: Sample is composed of grains of pre-existing minerals or rocks cemented together. Conglomerate, sandstone, and shale belong to this group. Non-Clastic: CHEMICAL OR BIOLOGICAL: Chemical sediments are formed by the precipitation of minerals (from a solution) during the evaporation of water (usually ocean water). In addition, sedimentary rocks can be formed by biological processes. Limestone, rock salt, dolostone, rock gypsum, and coal belong to these groups of chemical and biological sediments. SORTING: due to the settling of grains in water. Poorly and well-sorted varieties and those that are somewhere in between. E.g. Med. Well sorted or Med. Poorly sorted. POORLY SORTED: INTERMEDIATE SORTING: WELL SORTED: A wide variety of grain sizes and shapes are present. Sorting is intermediate between poorly sorted and well sorted. Most grains are the same size and shape. ROUNDING: due to the abrasion and erosion of corners on fragments. Well rounded and angular as well as those that are somewhere in between. E.g. Sub-rounded or sub-angular. WELL ROUNDED: SUB-ROUNDED SUB-ANGULAR: ANGULAR: grains are spherical. grains are have mostly rounded surfaces, but are not spherical: grains are mostly angular, but have some rounded surfaces. grains have jagged edges and are not spherical. 1

2 CEMENT: to become a rock, clastic (detrital) sediments must be cemented together. The most common types of cements in sedimentary rocks are: SILICEOUS: CALCAREOUS: colorless or white, chemical composition is SiO2. The same chemical composition as QUARTZ. chemical composition is the same as CALCITE. Calcareous cement will "FIZZ" when HCL acid is applied. FERRUGINOUS: contains iron. There are two types of ferruginous cement that you should be able to identify: LIMONITE (yellow-brown) and HEMATITE (red-brown). IN ADDITION, SOME SEDIMENTARY ROCKS CONTAIN FOSSILS OF PLANTS AND/OR ORGANISMS. IN GENERAL, IF A ROCK CONTAINS FOSSILS, THEN THE TERM FOSSILIFEROUS IS PLACE BEFORE THE ROCK NAME. (I.E. FOSSILIFEROUS LIMESTONE, FOSSILIFEROUS SANDSTONE, ETC.) METAMORPHIC ROCK TERMS: GRAIN SIZE FINE-GRAINED: MEDIUM-GRAINED: COARSE-GRAINED: You will not be able to see individual grains. You will be able to see individual grains, up to 2 mm. Grains are larger than 2 mm. FOLIATION FOLIATED: NONFOLIATED: A layered structure is developed in the rock. Folding and shearing may also be present. Foliated rocks contain parallel planes of platy minerals that have aligned due to the effects of pressure and recrystallization. Shows no layering. Exhibits a more uniform appearance. THE FOLLOWING QUESTIONS REFER TO CHAPTER 2 IN YOUR MANUAL (Read the questions from your manual and place your answers in the following spaces provided.) 1. Use Figures , 2.7, 2.9, 2.10, 2.11, 2.13, 2.19, 2.20, 2.21 (8 th edition) for this question. Of igneous, sedimentary, and metamorphic rocks which two of the three basic rock types appear to made of inter-grown (interlocking) crystals? 2. Which one of the two rock types you listed in question 1 have mineral grains or crystals aligned or arranged so that they point in the same direction in a linear, line-like manner? 3. Which one of the two rock types you listed in question 1 have the mineral crystals in most of the rocks arranged in a dense interlocking mass with no alignment? 4. Of the three rock types (igneous, sedimentary, or metamorphic) rocks are most often contain haphazardly arranged pieces or fragments, rather than crystals? (Select the best answer) 5. The igneous rock illustrated in Figure 2.9 A (8 th edition) is made of large mineral crystals that are all about the same size. The rock formed from magma that cooled (slowly, rapidly) and (inside, on/near the surface of) the Earth. (Select the best answers). 2

3 6. The rock shown in Figure 2.9 C (8 th edition) is made of mineral crystals that are all small and not identifiable without a microscope. The rock formed from magma that cooled (slowly, rapidly) and (inside, on/near the surface of) the Earth. (Select the best answers). 7. The igneous rock in Figure 2.9 G (8 th edition) has a porphyritic texture. The large crystals are called and the surrounding smaller crystals are called 8. The rocks in Figures 2.9 A and C (8 th edition) have nearly the same mineral composition. What fact about the mineral crystals in the rocks makes their appearances so different? What caused this difference? 9. Skip 10. Estimate the percentage of dark minerals contained in the igneous rock in Figure 2.11 D (8 th edition) (You may find the color index at the at the bottom of Figure 2.10 (8 th edition), Igneous & Rock Identification Key, helpful) The rock s color is (light, medium, dark, or very dark). Select the best answer. 11. skip 12. Use the specimens provided in the rock identification portion of this lab and identify the igneous rocks, samples 1 through skip Questions 13 through Of the samples provided for question 18 (samples 12 through 22), how many of the Sedimentary rock samples are Crystalline versus how many contain shells or shell fragments? Crystalline Shells or shell fragments 17. Skip 18. Use the specimens provided in the rock identification portion of this lab and identify the sedimentary rocks, samples 12 through Figure 2.13 C (8 th edition) is the rock sandstone that formed from sand. Where on Earth do you find sand, the primary material of sandstone, being deposited today? 20. Use Figure 2.16 (8 th edition) to name the environment(s) where, in the past, the sediment for the following sedimentary rocks may have been deposited. Use the following table: Rock type: Original Sediment Environment(s) Rock salt: Bituminous Coal Fossilferous Limestone: Travertine Quartz Sandstone: (precipitated halite) (carbon) (coral) (precipitated calcite) (wind faceted sand) 3

4 21. What characteristic can be used to distinguish Conglomerate from Breccia? (In other words, how would you tell them apart?) 22. From the rocks illustrated in Figure 2.19 A and C (8 th edition), the (slate, schist) resulted from more intensive heat and pressure. Select the best answer. 23. From the metamorphic rocks in Figure 2.19 B and D (8 th edition), the (phyllite, gneiss) shows the minerals separated into light and dark bands. Select the best answer. (The foliated-banded texture of the rock that you have selected often results from the most intensive heat and pressure during metamorphism) 24. skip 25. Use the specimens provided in the rock identification portion of this lab and identify the metamorphic rocks, samples 23 through 31. THE FOLLOWING QUESTIONS REFER TO THE SUMMARY / REPORT PAGE FOR CHAPTER 2 (Read the questions from your manual and place your answers in the following spaces provided.) 1. Write a brief definition of each of the three rock types: Igneous: Sedimentary: Metamorphic: 2. What unique factor about the arrangement of mineral crystals occurs in many metamorphic rocks? 3. Describe the basic difference between detrital and chemical sedimentary rocks. 4. Match each term or characteristic with the appropriate rock group: A. Slaty texture E. Glassy Texture I. Evaporite deposits M. Detrital rocks B. Silt-size particles F. Vesicular texture J. Strata or beds N. Felsic composition C. Porphyritic texture G. Lithification K. Alignment of mineral grains D. Foliated texture H. Clastic Texture L. Gneissic texture O. Chemical rocks Igneous Rocks: Sedimentary Rocks: Metamorphic Rocks: 4

5 5. Of the three basic rock types, which one is most likely to contain fossils? The following questions are for extra credit points! 6. Use the various tables and/or figures in your manual to identify the textures and composition of the following rocks: Rock type: Basalt: Quartzite: Coquina: Texture (Use the terms from pages 1 & 2 of this packet!) 7. What factor determines the size of the crystals in igneous rocks? Mineral content or description of composition, e.g. felsic, etc. 8. What is a good chemical test to determine the primary mineral in limestone? 9. What factor(s) determine(s) the size of crystals in metamorphic rocks? 10. If the sedimentary rock limestone is subjected to metamorphism, what metamorphic rock will likely form? 11. Referring to Figure 2.25 (8 th edition) Identify the rock s name and to which basic rock group it belongs. Fig D (8 th edition) Name: Fig E (8 th edition) Name: Fig F (8 th edition) Name: Rock Group: Rock Group: Rock Group: 12. Referring to Figure 2.23 A, B, & C (8 th edition) identify whether each outcrop is igneous, sedimentary, or metamorphic in origin. A. Outcrop A: B. Outcrop B: C. Outcrop C: CONTINUE ONTO THE ROCK IDENTIFICATION PORTION OF THIS LAB LOCATED ON THE FOLLOWING PAGES!! 5

6 ANDESITE BASALT DIORITE GABBRO GRANITE ROCK LIST - This list will be used for the ROCK Lab IGNEOUS ROCKS OBSIDIAN PUMICE RHYOLITE SCORIA (MEDIUM-LARGE VESICLES, LESS DENSE) and/or VESICULAR BASALT (VERY LARGE VESICLES, VERY DENSE) BRECCIA COAL CONGLOMERATE COQUINA SEDIMENTARY ROCKS FLINT and/or CHERT LIMESTONE (FOSSILIFEROUS) SANDSTONE (ARKOSE, QUARTZ) SHALE TRAVERTINE GNEISS MARBLE PHYLLITE METAMORPHIC ROCKS QUARTZITE SCHIST SLATE Igneous rocks may include the following terms in front of their names: Porphyritic, Vesicular, etc. For example, basalt is not the same as porphyritic basalt! Sedimentary rocks may include the term, Fossiliferous in front of the rock name. For example, fossiliferous shale is not the same as shale! ROCK IDENTIFICATION PORTION Samples 1 through 11 are igneous rocks, samples 12 through 22 are sedimentary rocks and samples 23 through 31 are metamorphic rocks. Igneous rocks: 1. What type of texture does this sample have?. 2. What type of texture does this sample have?. 3. What type of texture does this sample have? What type of texture does this sample have?.

7 5. What type of texture does this sample have?. 6. What type of texture does this sample have?. 7. What type of texture does this sample have?. 8. What type of texture does this sample have?. 9. What type of texture does this sample have?. 10. This sample has phenocrysts. What type of texture does this sample have?. 11. What type of texture does this sample have?. 7

8 Sedimentary rocks: 12. This rock WILL REACT WITH ACID! Is this rock fossiliferous?. What is the dominant mineral in this rock?. 13. This is an important economic rock. It is a biochemical rock that is composed of increasingly altered (compacted) plant remains. 14. This rock WILL REACT WITH ACID! Is this rock fossiliferous?. What is the dominant mineral in this rock?. 15. These samples are composed of SILICA. Grain size? (Coarse, medium, fine) 16. Grain size? (Coarse, medium, fine) What is the dominant mineral in this rock?. 8

9 17. This rock WILL REACT WITH ACID! Is this rock fossiliferous?. What is the dominant mineral in this rock?. Does this rock exhibit banding or layers?. 18. This rock may be fissile (breaks easily or flakes off easily) Grain size? (Coarse, medium, fine). 19. Grain size? (Coarse, medium, fine). Sorting? (well, medium, or poorly sorted). Rounding? (well-rounded, sub-rounded, sub-angular or angular). What is the dominant mineral in these samples?. 20. Grain size? (Coarse, medium, fine). Sorting? (well, medium, or poorly sorted). Rounding? (well-rounded, sub-rounded, sub-angular or angular). What is the dominant mineral in these samples?. 9

10 21. Sorting? (well, medium, or poorly sorted). Rounding? (well-rounded, sub-rounded, sub-angular or angular). 22. Grain size? (Coarse, medium, fine). Sorting? (well, medium, or poorly sorted). Rounding? (well-rounded, sub-rounded, sub-angular or angular). Metamorphic rocks: 23. Is it foliated?. Is it banded?. Grain size? (Coarse, medium, fine) 24. Grain size? (Coarse, medium, fine). What is the dominant mineral in this rock?. Is it foliated?. 25. Grain size? (Coarse, medium, fine). Is it foliated?. Does it have a silky luster?. 10

11 26. Grain size? (Coarse, medium, fine). Is it foliated?. 27. This is a monomineralic metamorphic rock, that WILL REACT WITH ACID. What mineral is it composed of?. Is it foliated?. 28. This is a monomineralic metamorphic rock. IT DOES NOT REACT WITH ACID. LOOK CLOSELY AND YOU WILL NOTICE THE "SUGARY" APPEARANCE. This sample WILL SCRATCH GLASS! What mineral is it composed of?. Is it foliated?. 29. Grain size? (Coarse, medium, fine). What are some the minerals in this rock?. Is it foliated?. Does it contain porphyroblasts?. 30. Grain size? (Coarse, medium, fine) Is it foliated?. Is it banded?. 31. This is a monomineralic metamorphic rock, that WILL REACT WITH ACID. What mineral is it composed of?. Is it foliated?. THE END!! HAVE A GNEISS DAY! 11