Assignment Module 1 Phy103
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1-2 Assignment: Minerals, Rocks, the Rock Cycle and Soils.
Southern New Hampshire University
PHY-103 Earth System Science
Minerals can be formally defined as inorganic, naturally occurring solids with organized crystalline structures. This means that minerals are not living, man-made, nor do they occur in
gaseous or liquid forms (Lutgens et al., 2021). A mineral’s crystalline structure is made up of either atoms or ions. These atoms or ions are arranged in a repetitive manner, creating crystals. Obsidian, while naturally occurring, inorganic and solid, is not a mineral due to its lack of crystalline structure. Minerals are only found in solid form. Ice is considered a mineral due to its crystalline and solid properties, but water is not. Minerals have various physical properties that are influenced by their chemical composition and crystalline structure. Two such physical properties are luster and hardness. A minerals luster is its reflective quality. Some minerals are more reflective than others. Some minerals have a shiny appearance regardless of their color. These minerals have a metallic luster .
Pyrite is an example of a mineral with a metallic luster. Pyrite is composed of iron sulfide (FeS
2
) and has a brass-yellow color that reflects light. Pyrite is formed at both high and low temperatures and occurs in metamorphic, igneous, and sedimentary rocks (King, n.d-a). Pyrite is a nonsilicate mineral and is a sulfide. Pyrite does not contain have a silicon-oxygen trihedron and
instead has oxygen ions (King, n.d-c).
Other metallic minerals are shiny until they are exposed to the elements. These minerals display a submetallic luster. Minerals that do not have a shiny appearance have what is called nonmetallic luster. There are numerous varieties of nonmetallic lusters. The most common variety of nonmetallic luster is vitreous. Approximately 70% of all minerals fall under the nonmetallic vitreous luster (King, n.d-a). The hardness of a mineral is measured by its resistance to abrasion. The Mohs scale is used to determine that resistance by giving minerals numerical value. The Mohs scale consists of
ten minerals arranged from softest to hardest. Talc being the softest and Diamond being the hardest. A mineral that does not have a hardness value is rubbed against minerals that have
known values. This will help determine the unknown minerals hardness value (Lutgens et al., 2021). Chrysoberyl has a hardness of 8.5 on the Mohs scale, meaning it is harder than topaz, but softer than a diamond. Chrysoberyl is a rare mineral composed of beryllium aluminum oxide (BeAl
2
O
4
), belonging to the nonsilicate oxide mineral group. Chrysoberyl contains negative oxygen ions that bond to positive ions and does not have silicon-oxygen tetrahedrons. Chrysoberyl is found in stream sediments, dolomitic marbles, and pegmatites. Its color ranges from brown to pale-yellow and from yellow-green to green (King, n.d-b). Pyrite Chrysoberyl
Metamorphic rocks are created from parent rocks, which can be igneous, sedimentary, or even other metamorphic rocks. Metamorphic rocks are created through metamorphism. Metamorphism is the change of a rock’s texture, composition, or structure by heat and/or pressure (Lutgens et al., 2021). There are two subtypes of metamorphic rocks, foliated and nonfoliated. Foliated rocks have layered mineral grains due to high pressure. When the parent rock is heated and highly compressed, minerals are flattened into parallel or almost parallel lines. Slate is an example of a foliated metamorphic rock. It is created from either shale or mudstone. It is composed of micas and clays. It can also contain quartz, calcite, pyrite, and hematite (King, n.d-d). Nonfoliated rocks occur in areas where there is not as much compression and deformation and the parent rocks have a simple chemical arrangement (Lutgens et al., 2021).
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The newly formed rocks have large interlocking crystals. Marble is an example of a nonfoliated rock, created by metamorphosizing limestone (King, n.d-e). During metamorphism, small calcite crystals grow into large calcite crystals that interlock.
Slate
Marble
Beneath the Earth’s surface the rock cycle starts. Magma is formed through the melting of rock in Earth’s upper mantle and within the crust. After magma is formed, it rises to Earth's surface. Once the magma reaches the surface and erupts it is called lava. The lava and magma eventually cool both above and below the Earth's surface. This cooled molten rock becomes igneous rocks. If the igneous rocks are formed above the crusts surface, the rocks are considered extrusive. If they are formed beneath the crust, they are considered intrusive. Igneous rocks that are exposed to the Earth's surface are eventually worn down by weathering, becoming sediment. The sediment is then transported by streams, rivers, glaciers, wind, or waves. Once the sediment is deposited in various areas, it continues to be buried by more sediment. Through the process of lithification, the sediment is compressed, thus converting it back into rock. There are three types of sedimentary rock. Clastic, chemical, and organic. Clastic sedimentary rocks are formed from accumulations of rock debris that is formed by weathering. Chemical sedimentary rocks are formed from ions produced during chemical weathering. Organic sedimentary rock is formed from organic materials that are compressed. The resulting sedimentary rock eventually becomes buried and subject to high heat and pressure, creating metamorphic rock. Metamorphic rocks
can be formed from both igneous and sedimentary rocks. Foliated metamorphic rocks are formed from high heat and pressure and immense folding. Nonfoliated metamorphic rocks are generally formed by minimal deformation and parent rocks that have a simple composition. If metamorphic rock is superheated deep within the Earth, it can melt back into magma, starting the rock cycle over again. Soil is found on the Earth’s surface and is vital to the sustainment of life. Soil is made up of minerals (45%), both living and dead organisms (organic matter) (5%), water (25%) and air (25%). In some areas soil may be multiple feet deep and in others less than an inch (Tignor, 2007). Soil has different physical properties including capacity to hold water, texture, size porosity and the horizon layers (
Basic Soil Properties
n.d). There are 3 main horizons that make up a soil profile, depending on depth. Horizon A, the surface horizon, is the top layer, and is made up of organic materials. Horizon B is the subsoil layer, which contains minerals and clay. This layer holds more water than horizon A. Horizon C
is the substratum layer and is made up of parent rock that is weathered down and decaying. (
A soil profile
n.d). Soil is broken up into twelve groups for the purposes of classification. Classification is used for understanding and describing soils. The classification groups are: Gelisols, Histosols, Spodosols, Andisols, Oxisols, Vertisols. Aridisols. Ultisols, Mollisols, Alfisols, Inceptisols and Entisols. The first of the groups are gelisols. Gelisols are soils that have permafrost within two meters of the soil surface. Histosols are soils made up of more than 20% organic matter. Spodosols are acidic forest soils that have an accumulation of metal-humus complexes. Andisols are formed from volcanic ash. Oxisols are found in tropical and subtropical areas. Vertisols are clay soils that have a large capacity to shrink and swell. Aridisols are as they sound. They are found in arid environments and have a subsurface horizon. Ultisols are leached, have subsurface clay and less than 35% base saturation. Mollisols are found in grasslands and have a highly saturated base. Alfisols have more than 35% base saturation, are moderately leached and have subsurface clay. Inceptisols subsurface horizons are weakly developed. The last group are
Entisols. Entisols are generally found near floodplains and dunes and have little to no horizon. They are young soils that make up approximately 18% of the Earth’s soil (
The Twelve Soil Orders
n.d). Lutgens, F. K., Tarbuck, E. J., & Tasa, D. G. (2021).
Foundations of Earth Science
(9th ed.). Pearson Education (US).
https://bookshelf.vitalsource.com/books/9780135851609
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King, H. M. (n.d.-a). Luster
. Geology.com https://geology.com/minerals/luster.shtml#metallic
King, H.M (n.d.-b). Chrysoberyl
. Geology.com. https://geology.com/minerals/chrysoberyl.shtml
King, H. M. (n.d-c). Pyrite . Geology.com. https://geology.com/minerals/pyrite.shtml
King, H. M. (n.d.-d). Slate
. Geology.com. https://geology.com/rocks/slate.shtml
King, H. M. (n.d.-e). Marble
. Geology.com. https://geology.com/rocks/marble.shtml
YouTube. (2007). Brief Soil Intro
. YouTube
. Retrieved from https://www.youtube.com/watch?
v=XNJFksa9sJc
. Basic Soil Properties
. Natural Resources Conservation Service. (n.d.-b). https://www.nrcs.usda.gov/sites/default/files/2023-
03/Soils2023_Day1_BasicSoilProperties.pdf
A soil profile
. Natural Resources Conservation Service. (n.d.). https://www.nrcs.usda.gov/resources/education-and-teaching-materials/a-soil-profile
The Twelve Soil Orders
. Soil Orders | Soil & Water Systems | University of Idaho. (n.d.). https://www.uidaho.edu/cals/soil-orders