GEOLOGY 306 Laboratory NAME: Instructor: TERRY J. BOROUGHS SECTION: 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 : large phenocrysts in a finer grained matrix Glassy : looks 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: The uniformity of grain sizes 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 or elliptical. grains have mostly rounded surfaces, but are not spherical or elliptical: grains are mostly angular, but have some rounded surfaces. grains have jagged edges and are not spherical. 1
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 SILTSTONE, 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. ROCK LIST - This list will be used for the ROCK Identification IGNEOUS ROCKS ANDESITE OBSIDIAN BASALT PUMICE DIORITE RHYOLITE GABBRO SCORIA (MEDIUM-LARGE VESICLES, LESS DENSE) or GRANITE VESICULAR BASALT (VERY LARGE VESICLES, VERY DENSE) 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! You may also so more than one rock type, but with different textures. SEDIMENTARY ROCKS BRECCIA FLINT CHERT LIMESTONE (Fossiliferous or Crystalline varieties) COAL SANDSTONE (ARKOSE and QUARTZ varieties) CONGLOMERATE SHALE COQUINA TRAVERTINE Sedimentary rocks may include the term, Fossiliferous in front of the rock name. For example, fossiliferous shale is not the same as shale! 2 GNEISS MARBLE PHYLLITE METAMORPHIC ROCKS QUARTZITE SCHIST SLATE You may see different examples that originated from different parent rocks, so that their mineral content may vary, but will still have the same textural characteristics. For example, a chlorite schist and a biotite schist may have different minerals present, but will both exhibit scaly foliation. ROCK IDENTIFICATION PORTION begins on the following pages..
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?. 4. What type of texture does this sample have?. 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?. 3
8. This sample has phenocrysts. What type of texture does this sample have?. 9. What type of texture does this sample have?. 10. What type of texture does this sample have?. 11. What type of texture does this sample have?. 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. 4
14. This rock WILL REACT WITH ACID! Is this rock fossiliferous?. What is the dominant mineral in this rock?. 15. This rock may be fissile (breaks easily or flakes off easily) Grain size? (Coarse, medium, fine). 16. Grain size? (Coarse, medium, fine). Sorting of particles? (well, medium, or poorly sorted). Rounding of particles? (well-rounded, sub-rounded, sub-angular or angular). What is the dominant mineral in these samples?. 17. Grain size? (Coarse, medium, fine). Sorting of particles? (well, medium, or poorly sorted). Rounding of particles? (well-rounded, sub-rounded, sub-angular or angular). What is the dominant mineral in these samples?. 5
18. Grain size? (Coarse, medium, fine). Sorting? of particles (well, medium, or poorly sorted). Rounding of particles? (well-rounded, sub-rounded, sub-angular or angular). 19. These samples are composed of SILICA. Grain size? (Coarse, medium, fine) 20. Grain size? (Coarse, medium, fine) What is the dominant mineral in this rock?. 21. 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?. 22. Sorting of particles? (well, medium, or poorly sorted). Rounding of particles? (well-rounded, sub-rounded, sub-angular or angular). 6
Metamorphic rocks: 23. Is it foliated?. Is it banded?. Grain size? (Coarse, medium, fine) 24. Grain size? (Coarse, medium, fine). Is it foliated?. 25. Grain size? (Coarse, medium, fine). Is it foliated?. Does it have a silky luster?. 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?. 7
29. This is a monomineralic metamorphic rock, that WILL REACT WITH ACID. What mineral is it composed of?. Is it foliated?. 30. Grain size? (Coarse, medium, fine). What are some the minerals in this rock, list at least one?. Is it foliated?. Does it contain porphyroblasts?. 31. Grain size? (Coarse, medium, fine) Is it foliated?. Is it banded?. 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. Of the samples provided for the Sedimentary rocks, samples 12 through 22, how many of the Sedimentary rock samples are Crystalline versus how many contain shells or shell fragments? a. Crystalline Shells or shell fragments 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.) 2. Write a brief definition of each of the three rock types: Igneous: Sedimentary: Metamorphic: 8
The following questions are for extra credit points! 3. Identify a potential parent rock for each of the following metamorphic rocks: a. Marble: b. Quartzite: c. Gneiss: d. Slate 4. Describe the basic (visual) difference between detrital and chemical sedimentary rocks. 5. 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: 6. Use the various tables and/or figures in your manual to identify the textures and composition of the following rocks: Rock type: GRANITE: Texture (Use the terms from pages 1 & 2 of this packet!) Mineral content or description of composition, e.g. felsic, etc. MARBLE: ARKOSE SANDSTONE: 9
7. What factor determines the size of the crystals in igneous rocks? 8. What is a good chemical test to determine the primary mineral in limestone? Identify the mineral being tested for as well. 9. What factor(s) determine(s) the size of crystals in metamorphic rocks? 10. Referring to Figure 2.25 (8 th edition) Identify the rock s name and to which basic rock group it belongs. Fig. 2.25 D (8 th edition) Name: Fig. 2.25 E (8 th edition) Name: Fig. 2.25 F (8 th edition) Name: Rock Group: Rock Group: Rock Group: THE END!! HAVE A GNEISS DAY! 10