Passage 2 | Geology
Classifying Earth’s Rocks
Our Earth is made up of a great variety of organic and inorganic compounds. At a fundamental level, though, its physical structure is primarily composed of rock. Deep within the Earth, rock exists at intense temperatures as liquid magma; closer to the surface, we find the solid rocks we are accustomed to seeing in the landscapes that surround us. These solid rocks are composites of different minerals, at times with some organic materials mixed in. Minerals are crystallized structures made up of either a single pure element or a mixture of elements. There are over 4,000 known species of minerals in our world, combining in various ways to create more than 100 different kinds of rocks.
One method of classifying rocks labels them according to the kinds of minerals ?c they contain: silicates, carbonates, sulfates, etc. However, there is an even more basic system for categorizing the multitude of rock types. Every rock on the planet can be put into one of three distinct groups based on T the processes that were responsible for its creation. These are the igneous, sedimentary, and metamorphic categories.
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Igneous rocks make up the majority of the Earth’s crust. They form when magma 30 is able to cool and solidify. Sometimes this happens below the Earth’s surface, when conditions change in a way that allows the ordinarily scalding subterranean temperatures to drop. The resulting igneous rocks are called intrusive, or plutonic. In other circumstances, magma manages to travel all the way to the crust, where it is ejected and then solidifies above the surface, creating extrusive, or volcanic, igneous rocks. From the term “volcanic,” it is easy to discern where such rocks may be found. Other places where magma comes to the surface to form extrusive igneous rocks include tectonic divergence zones, which are usually active deep underwater on the ocean floor. An igneous rock’s physical features depend on the location and duration of its cooling process in addition to its mineral composition.
While igneous rocks begin far beneath the crust as magma, sedimentary rocks form much closer to the surface. As the name implies, they are composed of numerous individual sediments, packed tightly together and forced into a fused state. Most of these sediments come from other rocks— igneous, metamorphic, or sedimentary— slowly broken apart by the weathering forces that occur on the Earth’s surface. Pieces of organic material, such as the shells of marine creatures or decaying plant matter, can be included in the mixture as well. Layers of these sediments are deposited in an area by wind or water and are slowly buried over time. As more and more debris accumulates on top of these layers, the underlying materials are subjected to increasing degrees of pressure, and this force eventually cements the once loose sediments into a thin, solid layer of rock, a physical change referred to as lithification. The characteristics of rocks of this type are influenced mostly by the size, shape, and mineral makeup of the sediments that coalesce to form them.
Metamorphic rocks can only develop 75 deep underground—up to 20 kilometers below the Earth’s crust. Tectonic activity is constantly pulling some landmasses down into the Earth while thrusting others up to the surface. Subducted rocks, which can belong to any of the three types, sometimes reach depths where the conditions of temperature and pressure are far different from the places where they were originally formed. Certain chemical changes result, producing new rocks that now fall into the metamorphic category. Though the temperatures and pressures that create metamorphic specimens must be intense enough to bring about such changes, they are not so great that the rocks melt and become magma. The specific strengths of these forces are the primary factors dictating what physical properties a metamorphic rock will display.
It is not difficult to see that all three types of rock are interconnected. [A] Igneous rocks at the surface are slowly weathered away, creating the building blocks for sedimentary rocks. [B] Once formed, these sedimentary rocks may be submerged to the point where they become metamorphic. [C] Some metamorphic rocks then reach depths with temperatures that can liquefy them, creating magma and beginning the entire process again.[D] In this way, the minerals and other materials that make up the Earth have been undergoing radical transformations for millennia.
15. The word composites in the passage is closest in meaning to
16 According to paragraph 1, which relationship is true?
(A) Rocks are made of minerals, which combine to form elements.
(B) Minerals are made of rocks, which are composed of one or more elements.
(C) Elements are made of minerals, which combine to form rocks.
(D) Rocks are made of minerals, which are composed of one or more elements.
17.The word its in the passage refers to
18. Why does the author repeat the term “volcanic” in paragraph 3?
(A) To fully explain a complicated geological concept
(B) To focus on the similarities between igneous and metamorphic rocks
(C) To emphasize the specific information that the name provides
(D) To illustrate the uniqueness of igneous rocks that form underwater
19. The word discern in the passage is closest in meaning to
20. According to paragraph 3, how are igneous rocks separated into two categories?
(A) By the type of volcano from which they are ejected
(B) By whether they form at high or low temperatures
(C) By the characteristics of the minerals they contain
(D) By whether they form above or below the surface
21. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
(A) Lithification occurs when a sediment mixture turns to solid rock as a result of the pressure it experiences when buried.
(B) As loose debris accumulates on the Earth’s surface, older sediments become more and more submerged until they change to rock.
(C) When sediments undergo the process of lithification, they form thin layers of solid rock beneath the ground.
(D) It is the pressure exerted by the weight of overlying materials that alters the physical properties of underground rocks.
22. The word coalesce in the passage is closest in meaning to
23. According to the passage, it can be inferred that plant and animal fossils are most commonly observed in
(A) crystallized minerals
(B) metamorphic rocks
(C) sedimentary rocks
(D) igneous rocks
24 What can be inferred about metamorphic rocks from paragraph 5?
(A) They melt before undergoing chemical changes.
(B) Their formation cannot be directly observed.
(C) There are not many specimens known to exist.
(D) They are the cause of Earth’s tectonic activity.
25 According to paragraph 5, what plays the biggest role in determining the characteristics of metamorphic rocks?
(A) The amounts of heat and pressure
(B) The content of the surrounding magma
(C) The chemicals in the original rocks
(D) The depth where formation occurs
26.The word radical in the passage is closest in meaning to
27. Look at the four squares m that indicate where the following sentence could be added to the passage.
Indeed, the materials involved in rock formation are part of a gradual yet continuous cycle that is constantly redistributing the matter of the Earth.
Where would the sentence best fit?
Click on a square  to add the sentence to the passage.
28. Directions: Complete the table by matching the phrases below.
Select the appropriate phrases from the answer choices and match them to the type of rock to which they relate.
TWO of the answer choices will NOT be used. This question is worth 4 points.
Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it To review the passage, click View Text
(A) Can contain particles of organic matter
(B) Form when soiid rocks are chemically altered
(C) Are composed of pure carbonate
(D) Form from accumulations of weathered debris
(E) Are the most common rocks in the crust
(F) Occur after materials are deeply submerged
(G) Retain the physical features of their constituent parts
(H) Occur anywhere that hot magma becomes solid
(I) Form when two different magma types merge