Examine the Rock Sample Here. Did It Form at the Surface or Below the Surface
Effigy one. The dissimilar colors and textures seen in this rock are caused by the presence of different minerals.
Introduction
There are iii types of rocks: igneous, sedimentary and metamorphic. Each of these types is role of the rock cycle. Through changes in conditions one rock type can become another rock type. Or it tin become a different stone of the aforementioned type.
What Are Rocks?
A stone is a naturally formed, not-living globe textile. Rocks are fabricated of collections of mineral grains that are held together in a firm, solid mass (figure i).
How is a stone unlike from a mineral? Rocks are made of minerals. The mineral grains in a stone may be then tiny that you tin can merely see them with a microscope, or they may exist as big as your fingernail or even your finger (effigy 1).
Figure 2. A pegmatite from S Dakota with crystals of lepidolite, tourmaline, and quartz (ane cm scale on the upper left).
Rocks are identified primarily by the minerals they contain and by their texture. Each type of rock has a distinctive set of minerals. A rock may be made of grains of all ane mineral type, such every bit quartzite. Much more commonly, rocks are fabricated of a mixture of different minerals. Texture is a description of the size, shape, and system of mineral grains. Are the two samples in figure 2 the same rock blazon? Exercise they have the same minerals? The same texture?
Figure 3. Stone samples.
| Sample | Minerals | Texture | Formation | Rock type |
|---|---|---|---|---|
| Sample 1 | plagioclase, quartz, hornblende, pyroxene | Crystals, visible to naked eye | Magma cooled slowly | Diorite |
| Sample two | plagioclase, hornblende, pyroxene | Crystals are tiny or microscopic | Magma erupted and cooled speedily | Andesite |
Every bit seen in table 1, these two rocks have the aforementioned chemical composition and incorporate mostly the same minerals, but they do not have the aforementioned texture. Sample i has visible mineral grains, but Sample 2 has very tiny or invisible grains. The two dissimilar textures bespeak different histories. Sample 1 is a diorite, a rock that cooled slowly from magma (molten rock) underground. Sample 2 is an andesite, a stone that cooled rapidly from a very similar magma that erupted onto World'due south surface.
Three Main Categories of Rocks
Rocks are classified into three major groups according to how they class. Rocks tin exist studied in hand samples that can be moved from their original location. Rocks tin can also exist studied in outcrop, exposed rock formations that are fastened to the ground, at the location where they are found.
Igneous Rocks
Igneous rocks form from cooling magma. Magma that erupts onto Earth'due south surface is lava, as seen in figure iv. The chemic limerick of the magma and the rate at which it cools determine what stone forms as the minerals absurd and crystallize.
Figure 4. This flowing lava is molten rock that volition harden into an igneous stone.
Sedimentary Rocks
Sedimentary rocks course by the compaction and cementing together of sediments, broken pieces of stone-like gravel, sand, silt, or clay (figure 5). Those sediments can be formed from the weathering and erosion of preexisting rocks. Sedimentary rocks also include chemical precipitates, the solid materials left behind after a liquid evaporates.
Figure 5. This sedimentary stone is fabricated of sand that is cemented together to form a sandstone.
Metamorphic Rocks
Metamorphic rocks form when the minerals in an existing rock are changed by heat or pressure within the World. Run across figure 6 for an example of a metamorphic rock.
Figure 6. Quartzite is a metamorphic rock formed when quartz sandstone is exposed to estrus and pressure inside the Earth.
A unproblematic explanation of the 3 rock types and how to identify them tin be seen in this video:
This video discusses how to identify igneous rocks:
This video discusses how to identify a metamorphic rocks:
This Scientific discipline Made Fun video discusses the atmospheric condition under which the three main rock types form:
The Rock Cycle
Figure 7. James Hutton is considered the Begetter of Geology.
Rocks change as a result of natural processes that are taking place all the fourth dimension. Most changes happen very slowly; many take identify below the World's surface, so we may non fifty-fifty notice the changes. Although nosotros may not see the changes, the physical and chemical backdrop of rocks are constantly changing in a natural, never-catastrophe cycle called the rock wheel.
The concept of the stone cycle was outset developed by James Hutton, an eighteenth century scientist often chosen the "Father of Geology" (shown in figure seven). Hutton recognized that geologic processes have "no [sign] of a beginning, and no prospect of an terminate." The processes involved in the rock cycle oft take place over millions of years. And so on the scale of a human being lifetime, rocks appear to exist "stone solid" and unchanging, but in the longer term, modify is always taking identify.
In the rock cycle, illustrated in figure 8, the three chief rock types—igneous, sedimentary, and metamorphic—are shown. Arrows connecting the three stone types testify the processes that change ane rock blazon into some other. The cycle has no showtime and no end. Rocks deep inside the Earth are right at present becoming other types of rocks. Rocks at the surface are lying in identify before they are side by side exposed to a process that volition change them.
Figure 8. The Rock Cycle.
Processes of the Stone Bike
Several processes can turn 1 type of rock into another type of rock. The key processes of the rock cycle are crystallization, erosion and sedimentation, and metamorphism.
Crystallization
Magma cools either underground or on the surface and hardens into an igneous rock. Every bit the magma cools, dissimilar crystals grade at different temperatures, undergoing crystallization. For case, the mineral olivine crystallizes out of magma at much higher temperatures than quartz. The rate of cooling determines how much time the crystals will have to form. Deadening cooling produces larger crystals.
Erosion and Sedimentation
Weathering wears rocks at the World's surface downward into smaller pieces. The minor fragments are called sediments. Running water, ice, and gravity all send these sediments from i place to another by erosion. During sedimentation, the sediments are laid down or deposited. In order to form a sedimentary rock, the accumulated sediment must become compacted and cemented together.
Metamorphism
When a stone is exposed to extreme heat and force per unit area inside the Globe only does non melt, the rock becomes metamorphosed. Metamorphism may alter the mineral composition and the texture of the rock. For that reason, a metamorphic stone may have a new mineral composition and/or texture.
Lesson Summary
- Rocks are collections of minerals of various sizes and types.
- The three main rock types are igneous, sedimentary, and metamorphic.
- Crystallization, erosion and sedimentation, and metamorphism transform one rock type into another or change sediments into rock.
- The rock cycle describes the transformations of 1 type of stone to another.
Reflection Questions
- What skill does this content assistance you develop?
- What are the central topics covered in this content?
- How can the content in this department help yous demonstrate mastery of a specific skill?
- What questions practise yous have about this content?
Source: https://courses.lumenlearning.com/geology/chapter/reading-the-rock-cycle/
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