A Study Guide for Learning. Rock Identification. Geology Department Green River Community College

Transcription

1 A Study Guide for Learning Rock Identification Geology Department Green River Community College

2 FORMAT: This Lab Study Guide consists of the following parts: PART I PART II PART III PART IV PART V (A-F) Minerals and Their Classifications Mineral Self-quiz Rocks and Their Classifications Rock Self-quiz Additional Self-quizzes EQUIPMENT: The following items should be in the drawer with the red label near the sink in SC110: 1) a glass plate to test hardness- (Be sure that the glass plate is flat on the table as you do the test-- do not hold the glass in your hand) 2) a 10X hand lens or magnifying glass to see the details of the sample surface 3) and a bottle of dilute hydrochloric acid, (HCl). (To test a sample go to the sink in the corner of SC 110. You must use the lab glasses to do the acid test. After testing the sample, wash the sample in the water and dry with a paper towel). GETTING STARTED: This Lab Study Guide is designed to guide you step-by-step through the process of rock and mineral identification. It is keyed to sample trays which will be in the cabinets in room SC 110. This room is available many times through the week for you to study the samples. Please leave these samples in SC 110 and be sure to return samples to the correct boxes as they are arranged according to the discussion which follows. THE GENERAL OVERVIEW: The names of rocks are broadly categorized into three major classes -- sedimentary, igneous, and metamorphic. One of the first steps in identification is to classify the samples into one of these categories. This decision is usually based on information about mineralogy and texture of the sample. The mineralogy is concerned with which minerals are present; while the texture represents the sizes and shapes of these mineral grains and their relationship to each other. The individual minerals in a rock are difficult to identify because the individual grains are small; but, the use of a hand lens and a little practice will alleviate this problem. Recognition of rock texture seems to be promoted mainly by experience and a few guidelines. Again, with practice, the difference in the major rock classes will become apparent. 2

3 PART I MINERALS AND THEIR CLASSIFICATION MINERALOGY A mineral is a naturally occurring, inorganic crystalline material with a unique chemical structure. Given that several thousand separate minerals have been identified, it is fortunate for us that only a few are common. In fact, fourteen such minerals comprise a good deal of the earth's crust. These fourteen minerals are found in PART 1: MINERALS. Find this box in the cabinet along the north side of SC 110. The usefulness of knowing the commonly occurring minerals may be illustrated with the following example. Find the sample of granite (C-1) in the mineral tray. This rock is composed of the following minerals: quartz (the gray mineral), potassium feldspar (the white mineral), and biotite or hornblende (the black minerals). Based on the identification of these three minerals and the coarse-grained texture (to be discussed later in Part III), the rock sample is identified as granite. Granite is a rock typically found in mountainous terrain and its presence indicates the area has experienced a significant amount of uplift and erosion in its history. Therefore, to interpret the history of a region, one must be able to identify the commonly occurring minerals. The next three mineral specimens B-1, B-2, and B-5, are larger samples of the quartz, potassium feldspar, and biotite found in the granite. The most useful properties of a mineral that aid in hand samples identification are the ones listed below: Color - One of the most obvious properties is color. However, one must be cautious using color as many minerals occur in many different colors (i.e., quartz may be pink, white, black, blue, green, red, purple, or colorless). Hardness - A physical property which does not change is hardness. Hardness is defined as the mineral's ability to resist scratching. For example, diamond is the hardest substance known and will scratch all other minerals. A relative scale of 1 to 10 has been established for use in mineral identification is termed the Moh's Hardness Scale (1 for talc and 10 for diamond). Some of the more common minerals on this scale are: (a reminder- do not hold the glass plate in your hand as you test the hardness of the minerals-please place the glass on the desk for the scratch test!) Hardness Mineral Description 1 Talc* Very soft, easily marked by a fingernail 2 Gypsum Soft, about the same hardness as a fingernail 3 Calcite Harder than a fingernail, but will not scratch glass 6 Feldspar Very common mineral 7 Quartz Harder than most common minerals * not included in the mineral trays 3

4 Some useful standard hardnesses that you may use to test specimens are: Hardness Fingernail Glass plate 5.5 Knife blade Find a glass plate in the top drawer in the cabinet in SC 110. Be sure to put the glass plate on a desk and do not hold the glass in your hand. Take the sample of quartz (B-1) and scratch the glass plate (you should not need a lot of pressure to scratch the glass). Now try calcite (B-11) on the plate. Does the calcite scratch the glass? What is the hardness of B-11? Cleavage - Fracture - When a mineral is broken it may cleave or fracture. Cleavage is created when the bonding between the rows of atoms in the mineral are weaker in some directions than others. This produces a flat surface which is repeated and will usually reflect light. On the other hand, fracture is an uneven, non-repeated, breakage which indicates that the bonding between the atoms is nearly equal in all directions, so no preferred breakage occurs. Sample B-11 is the mineral calcite which displays rhombic cleavage (like a deformed cube), while quartz, B-1, displays fracture. (Aside: Notice that there are two samples of quartz in the tray. B-1a is a small crystal of quartz. It appears at first that the crystal has cleavage but the outside surfaces are crystal faces. Why are these not cleavage faces?) In most minerals there is a combination of cleavage and fracture. For example, plagioclase feldspar, B-3, has two cleavages and the third side has fracture. Remember, you may see many cleavages, but if they are parallel (repeated) they count as one. Muscovite, B-4, is an example of a mineral with one cleavage. Notice all the parallel planes which count as one cleavage (see Figure 1). When there is more than one cleavage, we describe the angle of the intersection of the cleavage planes. For example, the angle of the plagioclase feldspar, B-3, is about 90 degrees, while calcite, B-11, is about 70 degrees (or the compliment of the angle). In many cases, you will have to use a hand lens to see the tiny cleavage surfaces. Go back to sample C-1, the granite, and look at the minerals with the hand lens. You should notice that the quartz (the clear gray mineral) has only fracture while the potassium feldspar (the white mineral) and the biotite (the black, flaky mineral) have cleavage. 4

5 5

6 Hornblende (B-6) and augite (B-7) are commonly confused because their outward appearance is similar. However, the cleavage angles are different; the hornblende is either 56 or 124 degrees, while the augite angles are at or near 90 degrees. Use the hand lens to examine samples B-6 and B-7. Notice that the broken surface in B-6 is similar to the sketch in Figure 1. The B-7 sample has 90 degree cleavage but it is difficult to see. Many times you have to "extend" the face to meet another, at 90 degrees. If you have trouble, ask for assistance - do not spend an excessive amount of time struggling to find the angles. Fortunately, there are other ways of separating hornblende and augite. Hornblende commonly occurs in long, slender grains (especially in volcanic rocks) while augite has shorter grains. In addition, hornblende and augite most commonly occur in different types of rocks (hornblende is common in granite, diorite, and light colored volcanic rocks, while augite is more common in gabbro and basalt). Luster - This is a reference to the appearance of the mineral when it reflects light. Notice that the plagioclase, B-3, is very shiny while the augite has a duller luster. Most of the samples have a vitreous luster. Luster found in other minerals not found in this unit include earthy, greasy, specular, metallic. Reaction with HCl - (reminder- you must do this test at the sink in SC 110) Dilute HCl will react with calcite- producing an effervesce (fizzing) when the HCl is dropped on the mineral. There are other minerals which will effervesce with dilute HCl, so it is necessary to combine this evidence with other physical properties such as cleavage, hardness, etc. The physical properties of the common rock-forming minerals are listed in the tables on the next two pages. After you have worked with the ten minerals in Part I and you feel that you can recognize the minerals, locate Part II - Mineral Self-Quiz in a separate box. 6

7 Sample number Mineral Hardness Cleavage Color B-1 Quartz 7 No cleavage Many different colors Diagnostic properties: The lack of cleavage and high hardness. May have six-sided crystal faces. Very common and found in all groups of rocks. B-2 Potassium Feldspar 6 Two at near 90 degrees White, salmon, pink, red, and green Diagnostic properties: Not as hard as quartz and has cleavage. Does not have striations like plagioclase. Found in all groups of rocks, but more common in igneous and metamorphic rocks. B-3 Plagioclase Feldspar 6 Two at near 90 degrees White (sodium variety) to dark gray (calcium variety) Diagnostic properties: Plagioclase is similar to potassium feldspar in hardness and appearance, however plagioclase has striations or parallel grooves that can be seen without a hand lens. Although plagioclase is found in sedimentary rocks, it is more common in igneous and metamorphic rocks. B-4 Muscovite 2-3 One cleavage Colorless, silvery, or yellowish Diagnostic properties: Member of the Mica group of minerals. Thin, transparent sheets and low hardness. Distinguished from biotite by lighter color. Found in sedimentary rocks, but more common in igneous and metamorphic rocks. B-5 Biotite 2-3 One cleavage Brown to black (slightly weathered biotite may be gold in color) Diagnostic properties: Member of the Mica group of minerals. Thin sheets, dark color, and low hardness. Rarely found in sedimentary rocks, but is common in intrusive igneous rocks and metamorphic rocks. B-6 Hornblende 5-6 Two cleavages at 56 and 124 degrees Brown to black Diagnostic properties: Member of the Amphibole group of minerals. Similar to Augite, but cleavage is different and hornblende grains are usually longer than they are wide. Hornblende is common in igneous and metamorphic rocks. 7

8 B-7 Augite 5-6 Two cleavages at near 90 degrees Dark green to black Diagnostic properties: Member of the Pyroxene group of minerals. Augite s cleavage is near 90 degrees and the grains are normally stubby and shorter than hornblende grains. Augite and other pyroxene minerals are more common in mafic and ultramafic igneous rocks. B-8 Olivine 7 No cleavage Olive to gray-green Diagnostic properties: Green color, high hardness, and sugary texture is common. Olivine is associated most often with mafic and ultramafic igneous rocks. B-9 Garnet 7 to 7.5 No cleavage Red, orange, brown, purple and green Diagnostic properties: Garnet is most often as small reddish-brown crystals in metamorphic rocks. Its high hardness, lack of cleavage, and common crystal faces helps in identification. B-10 Pyrite No cleavage Brassy, metallic Diagnostic properties: Also known as fool s gold. Pyrite is much harder than gold and fractures under direct stress. Also, pyrite s relatively high hardness for a metallic mineral. B-11 Calcite 3 Three Cleavages at near 70 degrees Many different colors Diagnostic properties: reaction to HCl, low hardness and the rhombic cleavage (like a deformed cube) B-12 Gypsum three cleavages one is common the other two are more difficult to find White, gray, colorless, red, and brown Diagnostic properties: Low hardness, no reaction to HCl. Commonly fibrous in the satin spar form of the mineral. B-13 Halite 2.5 Three cleavages at 90 degrees (cubic cleavage) Colorless to white Diagnostic properties: Low hardness, right-angle cleavage, no reaction to HCl B-14 Fluorite 4 Four cleavages (octahedral) Green, light green, blue, purple Diagnostic properties: softer than a glass plate, but harder than a finger nail, no reaction to HCl. Cleavage is common. 8

9 PART II: MINERAL SELF QUIZ After gaining confidence in the identification of the minerals, locate the self-quiz box labeled: PART II: SELF-QUIZ, and work through the quiz. The answers are on the back -- DO NOT check each answer as you do them, rather wait until you have finished the whole quiz. Remember, the effectiveness of this learning unit is dependent on how well you can spot your own weaknesses and then re-examine the items in which you have had problems. Circle the answer which is most correct: 1. Which of the following samples has the highest hardness? a. SQ 5 b. SQ 4 c. SQ 2 d. SQ 1 2. Which of the following samples has cleavage? a. SQ 4 b. SQ 3 c. SQ 6 d. SQ 1 3. Rhombic cleavage (like a deformed cube) is characteristic of which of the following samples? a. SQ 1 b. SQ 3 c. SQ 2 d. SQ 5 4. Sample SQ 1 is: a. hornblende b. potassium feldspar c. biotite d. muscovite 5. Sample SQ 2 is: a. quartz b. plagioclase feldspar c. olivine d. calcite 6. Sample SQ 3 is: a. quartz b. calcite c. olivine d. garnet 7. The reddish mineral in SQ 4 is: a. quartz b. augite c. calcite d. garnet 8. Sample SQ 5 is: a. plagioclase feldspar b. potassium feldspar c. calcite d. quartz 9. Sample SQ 6 is: a. quartz b. calcite c. plagioclase feldspar d. muscovite 10. Sample SQ 7 is: a. augite b. hornblende c. olivine d. garnet 11. The reddish brown mineral in SQ 8 is 12. The abundant black mineral in SQ 9 is 13. The abundant black mineral in SQ 10 is 9

10 ANSWERS TO THE MINERAL SELF-QUIZ 1. a. hardness of 6 should be scratched by SQ 4 b. CORRECT c. hardness of 3 should be scratched by SQ 5 and SQ 4 d. hardness of 2-3, should be scratched by a knife, SQ 5, and SQ 4 2. a. fracture, no cleavage, look again b. fracture, no cleavage, look again c. fracture, no cleavage, look again d. CORRECT 3. a. a platey cleavage, look again b. fracture, no cleavage, look again c. CORRECT fracture, no cleavage, look again 4. a. hornblende has cleavage of 56 or 124 degrees rather than the platey cleavage of SQ 1; hornblende is also harder potassium feldspar has right angle cleavage and is harder biotite has all the same properties with the exception of color; biotite is darker d. CORRECT 5. a. quartz is much harder and has fracture b. plagioclase feldspar has a hardness of 6 and usually exhibits striations c. olivine is much harder than SQ 2 and olivine exhibits fracture rather than cleavage d. CORRECT 6. a. the sugary, green texture of olivine is very similar to quartz; however, olivine is slightly softer b. calcite does not have conchoidal fracture and is not that hard c. CORRECT d. garnet does have the fracture, but may be slightly harder and is most commonly brownish to reddish in color 7. a. quartz has a very similar hardness to SQ 4 and both have fracture; however, garnet (the correct answer) is mostly red to brown and is slightly higher in specific gravity-- garnet usually occurs in small round crystals b. augite has right angle cleavage and is slightly softer c. calcite is softer and reacts to dilute HCl d. CORRECT 8. a. sample SQ 5 has all the physical characteristics of plagioclase but it does not have the striations. The striations appear to be like "record grooves"-- go back to the dark plagioclase and compare b. CORRECT c. calcite has different cleavage and is not that hard d. quartz has fracture and is harder than SQ 5 9. a. CORRECT b. if this were calcite, one would expect it to have rhombic cleavage, a hardness of 3, and react to dilute HCl c. if this were plagioclase, one would expect it to have some right-angle cleavage, a hardness of 6, and would have striations d. if this were muscovite, one would expect it to have platey cleavage, a hardness of 2-3, and a translucent-transparent character 10. a. augite is the mineral of which hornblende (the right answer) is most often mistaken. Augite has right angle cleavage and usually occurs in short, stubby grains b. CORRECT c. olivine has fracture rather than cleavage of SQ 7. Also, olivine is slightly harder d. garnet is harder, has fracture, and is most commonly red or brown 11. garnet 12. hornblende 13. biotite 10

11 PART III ROCKS AND THEIR CLASSIFICATION Now that you have mastered the properties of the common minerals, it is time to turn to the identification of rock textures. Each discussion will be followed by a table summarizing the principle means of identification. Sedimentary Rocks We separate sedimentary rocks into two main categories: clastic or detrital and chemical. The clastic rocks are composed of discrete grains or fragments of other rocks which have been weathered and eroded. An example is sample D-2 which is sandstone. The sand which comprises this sample was most likely from a river, beach, or sand dune which has subsequently been cemented together by either silica (quartz) or calcite. Aside: (Which cementing agent, quartz or calcite, will produce a rock which is more resistant to weathering?) We categorize clastic sedimentary rocks on the basis of the shape and size of the grains or fragments. The size of the grains in a clastic sedimentary rock may range from extremely small clay particles up to large rocks. Rocks which have grains larger than 2mm. are termed conglomerates (D-3). As noted above, sandstones (D-2) are composed of sandsized grains; siltstones (D-15) are composed of silt-sized grains; and shales (D-1) are composed of clay grains. The difference between shale (D-1) and siltstone (D-15) is not obvious at first. However, if you look closely, the silt-sized particles of the siltstone may be seen with a hand lens, while the grains in the shale are too small to be seen. The shape of the grains is also used as a means of identification for conglomerates (D-3) and breccias (D-4). The conglomerates are composed of rounded grains, while the grains in the breccia are the same size but angular. Aside: Why is the angularity of the grains important in interpretations of the history of the rock? Chemical sedimentary rocks are subdivided on the basis of mineral content. Most of the "chemical" sedimentary rocks are really deposited by organic means. Most of these rocks were originally thought to be chemical precipitates from sea water, but even though the theories involving their origin have changed the classification systems have not drastically changed. There are true chemical sedimentary rocks (such as salt and gypsum) but they will not be covered in this rock unit. 11

12 The most common of these rocks is limestone (D-6). Limestone may contain fossils, but will effervesce with addition of dilute HCl on a fresh fracture surface. Coal (D-10) is a true organic sedimentary rock and locally important in the Pacific Northwest. Coal is the record of past intense vegetation that has been covered and sealed from the atmosphere to prevent oxidation of the carbon. Coal ranges from hard and shiny (anthracite) to soft and dull (sub-bituminous) and is light in weight. Chert (D-7) is another sedimentary rock which is found occasionally in western Washington. In the San Juan Islands there are numerous exposures of ribbon chert (chert interlayered with siltstone). Chert is formed from shells of microscopic marine creatures in the deep oceans or by inorganic precipitation of silica. SEDIMENTARY ROCKS ROCK NAME SAMPLE # TEXTURE/COMPOSITION Clastic Sedimentary Rocks: CONGLOMERATE D-3 Course-grained (>2mm) (rounded grains) BRECCIA D-4 Course-grained (>2mm) (angular grains) SANDSTONE D-2 Medium-grained (1/16-2mm) (sand-sized grains) SILTSTONE D-15 Fine-grained (1/256-1/16mm) (silt-sized grains) SHALE D-1 Very fine-grained (less than (1/256mm; composed of clay) "Chemical" Sedimentary Rocks: LIMESTONE D-6 Calcite CHERT D-7 Silica COAL D-10 Plant material 12

13 Igneous Rocks In the identification of igneous rocks, one should first consider the texture of the sample. Sample C-2 (diorite) is an example of a coarse grained texture, while sample C-6 (andesite) is an example of a fine grained texture. The difference in these two rocks, which are chemically similar, is their cooling history. The fine-grained texture is a result of rapid cooling on or near the earth's surface; while the coarse grained texture is produced by the slow cooling of the magma deeper in the crust. The Pacific Northwest has an abundance of both coarse and fine grained igneous rocks. After the consideration of the texture, one should determine the color index of the sample. The color index is the percentage of dark minerals, such as biotite and hornblende, in the sample. Notice the difference between the sample of granite C-1 (color index about 10) and the sample of gabbro (color index of about 60). Although the color index is helpful in determining the general rock type, the actual classification of igneous rocks is based on the minerals in the rock. The granite has lots of quartz and potassium feldspar, while the diorite usually has less quartz and the feldspars are the light colored plagioclase (the sodium variety). The granodiorite has some quartz, and both potassium and light colored plagioclase feldspars. The gabbro has the dark colored plagioclase feldspar and usually either augite, hornblende, or both. In the table, listing the igneous rocks, the typical minerals present in the various rock types are listed. Two other igneous rocks which are found in the Pacific Northwest are volcanic breccia (C-12) and obsidian (C-11). The volcanic breccia has the same texture as the sedimentary breccia studied before in that there inclusions of other rocks in the sample and the angular grains are larger than 2mm. The difference is the material bonding the grains together. In the sedimentary breccia there is usually a sandy matrix which is bonded together by some type of cementing agent; while in the volcanic breccia, the matrix material is volcanic rock. One way in which the volcanic breccia forms is the inclusion of rocks from the walls of the volcanic pipe as the magma moves to the surface. It is also possible to get volcanic breccia as a lava flow includes rocks in the flow as it flows over the ground surface. The obsidian is a natural volcanic glass. It is usually black or red; it has glass-like fractures, and is usually shiny on a broken surface. Obsidian is found in lava flows in Oregon, Yellowstone, and California, but was traded extensively to make arrowheads by the indigenous people of North America. 13

14 IGNEOUS ROCKS Course-grained texture: ROCK NAME: COLOR INDEX MINERALS (Accessory minerals) GRANITE (C-1) Few dark minerals Potassium feldspar, quartz (biotite, hornblende) GRANODIORITE (C-21) potassium DIORITE (C-2) More plagioclase than feldspar, quartz (biotite, hornblende) Plagioclase feldspar, minor quartz (hornblende, biotite, augite) GABBRO (C-3) Mostly dark Dark plagioclase feldspar, augite minerals olivine, quartz rare Fine-grained texture: RHYOLITE (C-5) Light matrix (May have some quartz phenocrysts) DACITE (C-20) ANDESITE (C-6) (May have phenocrysts of quartz, hornblende, potassium feldspar) (May have phenocrysts of plagioclase feldspar, hornblende) BASALT (C-4) Very dark matrix (May have phenocrysts of plagioclase feldspar) Other Igneous Rocks: OBSIDIAN - (C-11), Volcanic glass usually black or dark red in color. VOLCANIC BRECCIA - (C-12), Angular fragments of included rock in a volcanic matrix 14

15 Metamorphic Rocks As in both the sedimentary and igneous rocks, texture should be your first consideration in the identification of metamorphic rocks. Metamorphic rocks are divided into those with foliation and those which may or may not have foliation. Find sample E-4. Foliation is the parallel alignment of minerals, such as the biotite in this sample of schist. The foliation developed at right angles to the pressure which was applied in the metamorphism of the rock. At high temperatures and pressures, bands of light and dark minerals will develop producing a rock called gneiss (E-2). The gneiss is usually coarser grained than the schist (E-4). Gneiss commonly appears to be granite-like, but if you study them closely you will see the foliation which determines that the sample is a gneiss. (Gneiss may be derived from either a sedimentary parent material or an igneous parent material). At first glance, the shale (D-1) is very similar to the metamorphic rock, slate (E-3). This should be expected as the parent rock for slate is the shale. The slate is harder and normally will have a "ring" when tapped against a hard surface. (normally the shale does not have this distinctive ring, but our samples of shale are harder than normal shale, therefore, the ring test is not sufficient to separate slate from shale.) Many times the slate will also display a higher degree of foliation while the shales are layered. Phyllites (E-5) may be separated from slate on the basis of the phyllite's shiny character. The shiny character is due to the development of platy minerals such as mica and chlorite. The grain size is larger than the slate but the grains are usually so fine that it is difficult to see them with your eye. Quartzites (E-6) and marbles (E-7) are examples of nonfoliated metamorphic rocks. Quartzites are logically mostly (95% or more) quartz. They are derived from the metamorphism of sandstone. The individual grains in the sandstone become interlocking due to the metamorphism. Go back and find the sandstone in the previous box and compare it to the quartzite using the hand lens. Marbles are from the metamorphism of limestones; therefore, both are mostly calcite and both will react to dilute HCl. The difference between a limestone and a marble lies in the interlocking nature of the calcite grains in the marble. Although quartzite and marble are classified as nonfoliated metamorphic rocks, they both may be banded (weakly foliated) from impurities in the sandstone or limestone. These banded varieties have been used extensively for building stones because they are very attractive. 15

16 I. Foliated Metamorphic Rocks METAMORPHIC ROCKS 1. Slate (E-3) Very fine-grained; dull luster; may be any color, but black is most common 2. Phyllite (E-5) Fine-grained; silky luster; may be any color 3. Schist (E-4) Medium-grained; mica is normally very abundant; parallel alignment of the mica flakes 4. Gneiss (E-2) Medium to coarse grained; alternating bands of light and dark minerals II. Nonfoliated Metamorphic Rocks 1. Quartzite (E-6) Mostly interlocking grains of quartz; sometimes foliated 2. Marble (E-7) Interlocking grains of calcite which will react with dilute HCl. May have distinctive banding 16

17 Circle the answer that is most correct. PART IV ROCK SELF-QUIZ 1. Quartzite may have foliation? (True or False) 2. To separate a granite and a rhyolite, one should consider their: a. composition b. color c. texture 3. Sample SQ 11 is a a. schist b. nonfoliated metamorphic rock c. rock with abundant hornblende d. all of the above 4. Sample SQ 12 is a a. slate b. phyllite c. schist d. quartzite 5. Sample SQ 13 is a a. shale b. siltstone c. sandstone d. slate 6. Sample SQ 14 is a a. coal b. obsidian c. limestone 7. Sample SQ 15 is a a. limestone b. gabbro c. diorite d. gneiss 8. Sample SQ 16 is most likely a. shale b. basalt c. limestone d. slate 9. Sample SQ 17 is a(n) a. granite b. diorite c. gabbro d. andesite 10. SQ 18 is a(n): 11. SQ 19 is a(n): 12. SQ 20 is a(n): a. andesite b. basalt c. limestone d. siltstone 13. Sample SQ 21 is most likely a. limestone b. andesite c. quartzite d. siltstone 17

18 ANSWERS TO THE ROCK SELF-QUIZ If you did not select the correct answer, make sure you go back to the section in the handout which covers that type of rock and determine why you made the error. 1. True. The presence of impurities may create a slight foliation although most of the rock consists of interlocking grains of quartz. 2. a. no, granite and rhyolite have approximately the same composition b. no, color in igneous rocks is a reflection of the composition c. CORRECT 3. a. CORRECT b. It is a foliated rock c. The abundant mineral is biotite d. above reasons 4. a. slates do not have the shiny appearance of SQ 12 b. CORRECT c. The separate minerals in SQ 12 are not large enough to be considered a schist d. quartzites are composed of quartz which is much harder than the very mica-like minerals in SQ a. the grain size is too large for a shale b. CORRECT c. the grain size is too small for a sandstone d. a slate would be foliated and would have a ringing sound when hit 6. a. CORRECT b. obsidian is much harder c. limestone should react to dilute HCl 7. a. limestone should react to dilute HCl and is softer the SQ 15 b. CORRECT c. diorite normally has more light-colored minerals and some quartz d. gneiss is foliated with light and dark bands 8. a. shales are softer and many times will have layering b. CORRECT c. limestones are softer (3-4) and will react with dilute HCl d. slates show foliation 9 a. CORRECT b. diorites contain more dark minerals and usually less quartz than a granite c. gabbro is much darker, reflecting the presence of calcic plagioclase and augite d. correct composition (color), wrong texture, andesite is fine grained 10. chert 11. gneiss 12. a. an andesite is harder and will not react to HCl b. basalt is darker c. CORRECT d. siltstones are composed of silt-sized particles rather than the massive nongranular texture of SQ a. If the sample were limestone it would effervesce with dilute HCl and would have a hardness of 3 b. CORRECT c. quartzites are harder and have interlocking quartz grains d. siltstones are softer and consist of silt-sized particles 18

19 PART V ADDITIONAL SELF-QUIZZES To provide additional experience in identification of rocks and minerals, additional self-quizzes are provided. Start with Part V - A (SQ 22) and work through Part V - F (SQ 111). After the answer, note whether the rock is igneous, sedimentary, or metamorphic. Again, the answers are given on the back of each page. PART V - A SQ 22 SQ 23 SQ 24 SQ 25 SQ 26 SQ 27 SQ 28 SQ 30 SQ 31 SQ 32 SQ 33 SQ 34 SQ 35 SQ 36 SQ 29 PART V - B SQ 37 SQ 38 SQ 39 SQ 40 SQ 41 SQ 42 SQ 43 SQ 45 SQ 46 SQ 47 SQ 48 SQ 49 SQ 50 SQ 51 SQ 44 19

20 Answers to Part V - A SQ 22- limestone (sedimentary) SQ 23- sandstone (sedimentary) SQ 24- rhyolite (igneous) SQ 25- basalt (igneous) SQ 26- dacite (igneous) SQ 27- diorite (igneous) SQ 28- conglomerate (sedimentary) SQ 30- obsidian (igneous) SQ 31-gabbro (igneous) SQ 32- schist (metamorphic) SQ 33- sandstone (sedimentary) SQ 34- breccia (sedimentary) SQ 35- granite (igneous) SQ 36- siltstone (sedimentary) SQ 29- coal (sedimentary) Answers to Part V - B SQ 37- gabbro (igneous) SQ 38- conglomerate (sedimentary) SQ 39- quartzite (metamorphic) SQ 40- basalt (igneous) SQ 41- gneiss (metamorphic) SQ 42- limestone (sedimentary) SQ 43- granodiorite (igneous) SQ 45- gneiss (metamorphic) SQ 46-shale (sedimentary) SQ 47- volcanic breccia (igneous) SQ 48- phyllite (metamorphic) SQ 49- conglomerate (sedimentary) SQ 50- limestone (sedimentary) SQ 51- dacite (igneous) SQ 44- sandstone (sedimentary) 20

21 PART V - C: SQ 52 SQ 53 SQ 54 SQ 55 SQ 56 SQ 57 SQ 58 SQ 60 SQ 61 SQ 62 SQ 63 SQ 64 SQ 65 SQ 66 SQ 59 PART V - D SQ 67 SQ 68 SQ 69 SQ 70 SQ 71 SQ 72 SQ 73 SQ 75 SQ 76 SQ 77 SQ 78 SQ 79 SQ 80 SQ 81 SQ 74

22 Answers to Part V - C SQ 52- andesite (igneous) SQ 53- siltstone (sedimentary) SQ 54- quartzite (metamorphic) SQ 55- obsidian (igneous) SQ 56- chert (sedimentary) SQ 57- granite (igneous) SQ 58- schist (metamorphic) SQ 60- diorite (igneous) SQ 61- gneiss (metamorphic) SQ 62- gabbro (igneous) SQ 63- rhyolite (igneous) SQ 64- conglomerate (sedimentary) SQ 65- quartzite (metamorphic) SQ 66- breccia (sedimentary) SQ 59- sandstone (sedimentary) Answers to Part V - D SQ 67- gneiss (metamorphic) SQ 68- limestone (sedimentary) SQ 69- volcanic breccia (igneous) SQ 70- basalt (igneous) SQ 71- sandstone (sedimentary) SQ 72- basalt (igneous) SQ 73- andesite (igneous) SQ 75- volcanic breccia (igneous) SQ 76-quartzite (metamorphic) SQ 77-gabbro (igneous) SQ 78- shale (sedimentary) SQ 79- gneiss (metamorphic) SQ 80- obsidian (igneous) SQ 81- granodiorite (igneous) SQ 74- phyllite (metamorphic)

23 PART V -E SQ 82 SQ 83 SQ 84 SQ 85 SQ 86 SQ 87 SQ 88 SQ 90 SQ 91 SQ 92 SQ 93 SQ 94 SQ 95 SQ 96 SQ 89 PART V - F SQ 97 SQ 98 SQ 99 SQ 100 SQ 101 SQ 102 SQ 103 SQ 105 SQ 106 SQ 107 SQ 108 SQ 109 SQ 110 SQ 111 SQ 104

24 Answers to Part V - E SQ 82- chert (sedimentary) SQ 83- granite (igneous) SQ 84- phyllite (metamorphic) SQ 85- siltstone (sedimentary) SQ 86- sandstone (sedimentary) SQ 87- conglomerate (sedimentary) SQ 88- granodiorite (igneous) SQ 90- coal (sedimentary) SQ 91- gneiss (metamorphic) SQ 92- gabbro (igneous) SQ 93- basalt (igneous) SQ 94-limestone (sedimentary) SQ 95- gneiss (metamorphic) SQ 96- breccia (sedimentary) SQ 89- schist (metamorphic) Answers to Part V - F SQ 97- granite (igneous) SQ 98- breccia (sedimentary) SQ 99-marble (metamorphic) SQ 100- diorite (igneous) SQ 101- gneiss (metamorphic) SQ 102- andesite (igneous) SQ 103- schist (metamorphic) SQ 105- gabbro (igneous) SQ 106- andesite (porphyritic)** (igneous) SQ 107- quartzite (metamorphic) SQ 108- dacite (igneous) SQ 109- andesite (igneous) SQ 110- sandstone (sedimentary) SQ 111- diorite (igneous) SQ 104- phyllite (metamorphic) ** this sample has a porphyritic texture it is not a volcanic breccia because the included pieces are crystals, not included fragments of other rocks