4430, ESCI Fall 2008 Sample Completed Assignment #2: Rocks [presumes a previous unit on Minerals] Objectives: The student will be able to: 1. Classify rocks by their process of formation (GPS 6th) a. including igneous, metamorphic, and sedimentary (AKS 6th) i. Describe how the grain size (texture) of igneous rocks reflects the speed and depth at which they cooled from magma (text) ii. Describe how sedimentary rock is formed as accumulated sediments are gradually buried, compacted, and cemented together by dissolved minerals to form solid rock again, periodically embedding plant and animal remains and leaving a record of the sequence in which the plants and animals appeared and disappeared (Benchmarks 8th) iii. Describe the general conditions and location in which metamorphic rocks form, and the nature of changes in properties that they can undergo as a result. (Benchmarks 8th) b. with reference to their chemical composition and combinations of minerals that they contain (Benchmarks 5th) 2. Describe processes that change rocks and the surface of the earth. (GPS 6th) a. including weathering, erosion, transport, and deposition (Benchmarks 5th) i. including the relationship between the ease of weathering of an igneous rock at the surface of the Earth and the temperature at which the minerals it contains crystallized as the magma cooled. (added) ii. including the relative depth of ocean water in which sand, mud/clay, and lime sediments most typically accumulate (added) iii. including the ease of chemical weathering of rocks (such as limestone and marble) composed of calcium carbonate by acidic liquids, such as rainwater (added) 3. Recognize examples of the most common specific types of rock, either as actual samples or given descriptions of their color, texture, mineral composition, specific origin, or most common location. (text) a. basalt b. granite c. shale d. sandstone e. conglomerate f. coal g. limestone h. slate i. schist j. gneiss k. quartzite l. marble 4. Recognize and list examples of rocks commonly found today in locations (especially elevations) very different from where they were formed. (text) 5. Given a partially or largely incomplete diagram of the rock cycle, complete the diagram
by providing the names of missing processes or types of rock. (text) 6. Recognize the definitions of the following scientific terms (in addition to those already used in the previously listed objectives), how the concepts they represent compare, contrast, or relate to each other, and how to apply the concepts they represent to specific example and instances (text or added): a. extrusive or volcanic b. intrusive or plutonic c. porphyritic d. clastic [sedimentary rocks] e. organic [sedimentary rocks] f. uplift g. foliated
I. Multiple-choice questions [Bloom's level; corresponding objective(s)]: Rocks that form from magma are referred to as [knowledge; 1a] A. igneous B. metamorphic C. organic D. sedimentary E. all of the above F. none of the above Metamorphic rocks are changed from previously existing rocks by [knowledge; 1a] A. cementation B. deposition C. heating and pressure D. melting and cooling E. all of the above F. none of the above Coral reef rock is an example of [comprehension; 3g] A. calcite B. calcium carbonate C. limestone D. organic sedimentary rock E. all of the above F. none of the above Basalt [knowledge; 3a] A. has a fine-grained texture B. is an extrusive rock C. is an igneous rock D. is always dark in color E. all of the above F. none of the above Sandstone is always [knowledge; 3d] A. clastic B. fine-grained C. foliated D. light in color E. all of the above F. none of the above
Granite is [knowledge; 3b] A. common in continental crust B. common in oceanic crust C. porphyritic D. organic E. all of the above F. none of the above Coarse-grained igneous rock forms by [comprehension; 1.a.i] A. cooling quickly at or near the surface of the Earth B. cooling quickly deep underground C. cooling slowly at or near the surface of the Earth D. cooling slowly deep underground E. all of the above F. none of the above Metamorphic rocks are usually most similar to the original rocks from which they were formed in their [comprehension; 1.a.3] A. foliation B. chemical composition C. texture D. taste E. all of the above F. none of the above A porphyritic texture in an igneous rock indicates that the magma from which it formed [comprehension; 1.a.1, 6c] A. cooled first slowly, then quickly B. cooled first quickly, then slowly C. contained a high proportion of silica (SiO2) D. contained a high proportion of iron and magnesium E. contained dissolved gases, which formed bubbles F. all of the above G. none of the above The sediment at the bottom of the Oconee River consists of many rounded pebbles, surrounded with some sand, silt, and mud. If this river bed is eventually deeply buried and hardened into sedimentary rock, it would be referred to as [application; 3e] A. gneiss B. sandstone C. schist D. shale E. all of the above F. none of the above Aside from the artificial beach created by trucking and dumping sand near its shore, the sediment
at the bottom of Lake Herrick consists primarily not of weathered rock but of decayed remains of plants. If this lake bed is eventually deeply buried and hardened into sedimentary rock, it would be referred to as [application; 3f] A. coal B. conglomerate C. gumbo D. slate E. all of the above F. none of the above Most of the vast amounts of extremely fine sediment famously carried by the Mississippi River end up being dumped into the Gulf of Mexico, where it spreads out, settles to the bottom, and can accumulate to great thicknesses. If this ocean bed is eventually deeply buried and hardened into sedimentary rock, it would be referred to as [application; 3c] A. coal B. gumbo C. Mississippi Mud Pie D. shale E. all of the above F. none of the above Extrusive/volcanic rocks are nearly always [comprehension; 1.a.i, 6b] A. fine-grained B. high in silica (SiO2) C. high in iron and magnesium D. light in color E. all of the above F. none of the above [Lab rock sample: gabbro] This rock is [application; 1.a.i, 1b] A. extrusive/volcanic, containing large amounts of quartz B. extrusive/volcanic, containing little or no quartz C. intrusive/plutonic, high in iron and magnesium D. intrusive/plutonic, high in silica (SiO2) E. all of the above F. none of the above [Lab rock sample: rhyolite] This rock is [application; 1.a.i, 1b] A. extrusive, containing large amounts of quartz B. extrusive, containing little or no quartz C. intrusive, high in iron and magnesium D. intrusive, high in silica (SiO2) E. all of the above F. none of the above [Lab rock sample: quartzite] This rock does not fizz with acid and is metamorphic. What kind of
rock is it most likely to have originally been? [application; 1b, 3k, 3l] A. basalt B. limestone C. sandstone D. shale E. all of the above F. none of the above [Lab rock sample: basalt] This rock [knowledge; 3a] A. makes up most of the continental crust B. makes up most of the oceanic crust C. is prophyritic D. is organic E. all of the above F. none of the above [Lab rock sample: granite] This rock [knowledge; 3b] A. makes up most of the continental crust B. makes up most of the oceanic crust C. is porphyritic D. is organic E. all of the above F. none of the above II. Short-answer questions: (2 points) Explain why, for two igneous rocks of similar grain size, darker-colored a one will chemically weather more readily than a lighter-colored one in the conditions found at the surface of the Earth. (Hint: The most efficient explanation would refer to Bowen's Reaction Series.) [comprehension; 2.a.i]
Grading rubric: 1 point for stating that, in general, darker-colored minerals crystallize out of a cooling magma at higher temperatures than do lighter-colored minerals 1 point for stating that therefore darker colored minerals are less stable (the anthropomorphic expression happy may be accepted) at surface conditions, since they are in an environment that is much more different (much, much, lower temperature) than the one in which they formed. No points for inaccurate and/or largely irrelevant statements, including but not limited to: dark minerals would absorb more solar energy; dark minerals tend to have a lower hardness; the most common rocks in which dark minerals predominate are fine-grained.
(2 points) Explain why fossil remains of animals and plants are commonly found only in sedimentary rock. [comprehension; 1.a.2]
Grading rubric: 1 point for stating that being encased in sediment can sometimes protect fossil material and/or that the pressure of burial does not necessarily obliterate or distort them 1 point for stating that the extremely high heat and/or pressure conditions under which igneous and metamorphic rocks form would usually destroy any fossils
(4 points) Stone Mountain, near Atlanta, is an example of a granite batholith. While climbing up
it, there are readily visible effects of extensive weathering. Describe the rock of which Stone Mountain is composed in terms of color, texture, general mineral composition, and age. [application; 2.a.1, 3b]
Grading rubric: 1 point for stating that it is generally light in color 1 point for stating that it is coarse-grained 1 point for stating that it is relatively high in quartz and orthoclase (potassium feldspar) 1 point for stating that it has been exposed at the surface for a relatively long time, since it is significantly weathered 1 extra point for stating that, since most of the minerals in granite are fairly stable and difficult to weather (compared to darker rocks), that this further supports the idea that the rock has been exposed to the surface for a long period of time
(4 points) The floor of the volcanic crater known at Halemaumau in Hawaii consists of completely flat-lying basalt. While walking across it, there are virtually no visible effects of weathering. Describe the rock of which Halemaumau is composed in terms of color, texture, general mineral composition, and age. [application; 2.a.1, 3a]
Grading rubric: 1 point for stating that it is generally dark in color 1 point for stating that it is fine-grained 1 point for stating that it is relatively high in calcium feldspar, amphiboles and pyroxenes 1 point for stating that it has been exposed at the surface for a relatively sort time, since it is not significantly weathered 1 extra point for stating that, since most of the minerals in basalt are fairly unstable and easy to weather (compared to lighter rocks), that this further supports the idea that the rock has been exposed to the surface for quite a (geologically) short period of time
(3 points) The rock visible in roadcuts along Interstate 85 South in northeastern Atlanta is a gneiss, visibly foliated on a very large scale. Explain the general conditions under which this rock must have formed, and what this implies about large-scale geologic changes that have occurred to the Atlanta area over a long period of time. [application; 1.a.iii, 3j, 6g, 4]
Grading rubric: 1 point for stating that, since it is foliated, it must be a metamorphic rock 1 point for stating that therefore it must have formed deep underground, under great pressure and probably quite high temperature [If these first two points are combined without the use of the term metamorphic, that is sufficient.] 1 point for stating that therefore the Atlanta area must have been significantly uplifted, deeply eroded, or both, at some point in geologic history, since this rock that was once deep underground is now exposed at the surface.
(1 point) Explain how it is possible that tilted beds of limestone and shale containing fossil seashells are found today near the peaks of some of the world's highest mountains. Hint: Refer to the action of Plate Tectonic forces over time. [application; 4]
Grading rubric: 1...