3 ELS_MT_LESSON3_ROCKS AND MINERALS.docx.pdf

FEU High School Earth and Life Science Module 3| AY 24-25 LESSON 3: MINERALS AND ROCKS SUBJECT MATTER If you remember from our previous lesson on the solar system, our planet is a terrestrial planet. This means that our home is a ball of rock. T...

FEU High School Earth and Life Science Module 3| AY 24-25 LESSON 3: MINERALS AND ROCKS SUBJECT MATTER If you remember from our previous lesson on the solar system, our planet is a terrestrial planet. This means that our home is a ball of rock. The chemical elements comprising our planet are unequal in abundance and unevenly distributed. These elements may combine and form compounds that make up a wide array of geological materials such as minerals and rocks. Today, we will focus on how rocks are formed and how they shape our planet. Minerals Are minerals similar to a rock? Minerals are the building blocks of rocks and have been used for both functional and decorative designs for thousands of years. What is a mineral? To meet the definition of mineral used by most geologists, a substance must have the following characteristics: 1. Naturally occurring – It is made by natural processes. Any material that is created, formed, or produced in laboratories or artificial conditions is not considered a mineral. 2. Inorganic – The process of creating, forming, or producing a mineral by natural means is extended further by making sure that no organic material or the substance is not made by an organism. This means that any hard parts of an organism such as bones and teeth or produced by an organism such as pearls are not minerals. 3. Solid – The substance is neither liquid nor gas at standard room temperature and pressure. 4. Definite chemical composition – A mineral must also possess uniformity in its chemical composition. This means, a mineral must have a definite chemical constituent. 5. Ordered internal/crystalline structure – The atoms in a mineral are arranged in a systematic and repeating pattern. Knowing what characteristics, a substance or material should possess to be considered as a mineral, in your own understanding or in your own words, can you define what a mineral is? FEU High School Earth and Life Science Module 3| AY 24-25 Mineraloids Any material which possesses most of the characteristics mentioned above is considered as mineraloid. Most of the time, mineraloids are naturally occurring, inorganic, solid, have definite chemical compositions but do not possess ordered internal/crystalline structure. Examples of mineraloids would be volcanic glass and opal. Properties of Minerals Imagine you have material that possesses all the characteristics we discussed earlier. You have identified that the material you have is a mineral. You now want to identify this mineral. In this section, we will discuss the different properties of minerals that will help you identify them. 1. Color – It is the perceived wavelength of light that bounces off from the material and is detected by our eyes. Most of the time, the composition dictates what color/hue the mineral will take. But for some, the crystalline structure will also play a role. There are instances where color becomes a diagnostic property of a mineral. This means that the mineral will only exhibit a single color regardless of where it came from. It should be FEU High School Earth and Life Science Module 3| AY 24-25 noted that most minerals show a wide range of colors depending on the impurities that are present in them. 2. Streak - it is the color of a mineral in powdered form. Minerals show color differently when ground into fine powder. This is because the presence of smooth surfaces of compact crystals sometimes reflects light differently compared to a powdered mass. In most cases, minerals will show streak color equivalent to its normal massive color. But in rare cases, streak color will differ from its compact form. 3. Luster – It is the quality and intensity of reflected light exhibited by the mineral. In describing luster, minerals are characterized as being metallic or non-metallic. Minerals having metallic luster reflect light like a polished metal, but this does not necessarily mean that a mineral has metallic elements in its composition. On the other hand, materials that closely resemble the luster of a non-metallic mineral will suffice for description purposes. There are many descriptive terms to describe non-metallic luster such as: a. Pearly – looks like the surface of a pearl. b. Waxy – like a surface of a candle c. Vitreous – like clear or stained glass d. Adamantine – possesses a brilliant, superlative luster. Adamantine minerals are transparent or translucent. FEU High School Earth and Life Science Module 3| AY 24-25 e. Silky – like silk cloth (shiny, fibrous body appearance) f. Resinous – it has an appearance of resin, chewing gum or smooth-surfaced plastic g. Dull – it has a non-reflective appearance h. Earthy – it looks like dirt, or dried mud, while others may be rough and porous in texture. It may also look like unglazed pottery or has a granular texture with a freshly broken appearance. 4. Hardness – It is the resistance of a mineral to scratching. It should be noted that scratching is different from breaking. In determining hardness, the mineral is tested by scratching the surface with a measurable amount of force. The minimum force applied on the surface before showing evidence of scratching will be the hardness of the mineral. We use the Moh’s Hardness Scale to determine the hardness of a mineral. Using different minerals with set FEU High School Earth and Life Science Module 3| AY 24-25 hardness, the unknown mineral should be scratched by a harder mineral. 5. Cleavage – A mineral tends to break in certain directions. This breakage happens along zones of weakness within the crystal structure of the mineral. When force is applied to a mineral, it tends to separate into regions where bonding is weaker. The presence of cleavage in a mineral is independent of its hardness. Even diamonds exhibit cleavage. Cleavage can be described as perfect, good, fair, or poor. This is dependent on how sharp or defined the planes where the mineral splits. In cases where there is no observable planar cleavage, the mineral is said to have fracture. FEU High School Earth and Life Science Module 3| AY 24-25 6. Specific Gravity refers to the ratio of mineral density and water density. This parameter indicates how many times more the mineral weighs compared to an equal amount of water. 7. Other Properties a. Magnetism – the tendency of a mineral to be attracted to a magnet. Any mineral that shows attraction to a standard magnet is considered magnetic. b. Fluorescence – Some minerals, when exposed to certain wavelengths of light, will glow, or appear to release a certain light. This phenomenon is known as fluorescence. FEU High School Earth and Life Science Module 3| AY 24-25 c. Reaction to Chemicals – Minerals, because of their definite chemical compositions, will react at certain conditions to different chemicals. The most common test is called the acid test, wherein dilute hydrochloric acid (HCl) is allowed to react with a mineral. Because HCl is a strong acid, minerals composed of basic components such as carbonates (CO3-2) will readily react with the acid to form neutral salts. d. Taste – Some minerals will exhibit taste like salty, sweet, or bitter. It should be noted however that a large portion of minerals are not safe to eat (hence, taste is often not used for identification of minerals). There are few minerals that are identifiable because of their taste. e. Odor – Certain minerals give off a distinct smell like some spices or industrial materials. It should be noted however that some minerals may cause harmful effects once they get into our bodies (from inhaling or tasting). Mineral Groups A few minerals make up most of the rocks on the Earth’s crust. They are referred to as rock-forming minerals. Minerals can be categorized according to their chemical composition. FEU High School Earth and Life Science Module 3| AY 24-25 1. Silicates – These are minerals containing silicon and oxygen. When linked together, these two elements form orthosilicate or silicon-oxygen tetrahedron (SiO4), which is the fundamental building block of silicate minerals and over 90% of rock-forming minerals belong to this group. FEU High School Earth and Life Science Module 3| AY 24-25 2. Oxides – Minerals composed of oxygen anion (O2-) combined with one or more metal ions. 3. Sulfates – Minerals containing sulfur and oxygen in the form of (SO4)- anion. 4. Sulfides – Minerals containing sulfur and a metal. FEU High School Earth and Life Science Module 3| AY 24-25 5. Carbonates – These are minerals containing the carbonate anion (CO3)-2 combined with other elements. 6. Halides – Minerals that contain halogens combined with one or more metals. 7. Native Elements – Minerals that form from individual elements. a. Metals and Intermetals – minerals with high thermal and electrical conductivity, typically with metallic luster, and low hardness. b. Semi-metals – minerals that are more fragile than metals and have lower conductivity. c. Non-metals – non-conductive elements. FEU High School Earth and Life Science Module 3| AY 24-25 Rocks Rocks are an aggregate of minerals. It can be composed of a single mineral, or more commonly, as an aggregate of two or more minerals. A mineral name can be used as a rock name. We have discussed earlier what minerals are and the properties used to identify them. Rocks are classified into three main groups based on how they were formed. A rock can be classified either as igneous, metamorphic, or sedimentary. Types of Rocks Igneous rocks are formed when molten rock material (magma or lava) cools and hardens. Molten rock material can solidify below the surface of the Earth (intrusive igneous or plutonic igneous rocks) or at the surface of the Earth (extrusive igneous or volcanic igneous rocks). Note FEU High School Earth and Life Science Module 3| AY 24-25 that the rate of cooling is one of the most important factors that control crystal size and the texture of the rock in general. Igneous rocks may be characterized by their texture and composition. Texture describes the overall appearance of the rock based on the size, shape, and arrangement of their interlocking crystals. The rate of cooling strongly influences crystal size. Slow cooling of magma results in the formation of large crystals (intrusive igneous or plutonic igneous rock). On the other hand, rapid cooling results in the formation of small crystals (extrusive igneous or volcanic igneous rock). a. Coarse-grained – the grains (crystals) can be seen with the naked eye b. Medium-grained – the grains (crystals) can only be seen through a hand lens c. Fine-grained – the grains (crystals) can only be seen through the microscope A mineral’s composition is based on the chemical makeup of magma. Rocks may be divided according to their coloration: a. Light-colored – such as granite and rhyolite b. Medium-colored – such as diorite and andesite c. Dark-colored – such as gabbro and basalt FEU High School Earth and Life Science Module 3| AY 24-25 The table below shows the classification of common igneous rocks based on their texture and color. Texture Color Light Medium Dark Coarse-grained Granite Diorite Gabbro (Intrusive) Fine-grained Rhyolite Andesite Basalt (Extrusive) Sedimentary rocks are formed from previously existing rocks that have been broken down into smaller particles or have been dissolved in solutions. These particles are transported by moving water and are deposited as sediments. These sediments accumulate and pile on top of one another. The weight of each deposited layer of sediments increases the pressure on the lower layers, squeezing water out and packing the particles tighter in a process known as compaction. Chemical deposits then fill the spaces between the particles, precipitate, and hold the particles together. This process is known as cementation. There are three basic types of sedimentary rocks. FEU High School Earth and Life Science Module 3| AY 24-25 1. Clastic sedimentary rock - such as breccia, conglomerate, sandstone, siltstone, and shale are formed from mechanical weathering debris. 2. Chemical sedimentary rocks - such as rock salt, iron ore, chert, flint, some dolomites, and some limestones, form when dissolved materials precipitate from solution. 3. Organic sedimentary rocks – such as coal, some dolomites, and some limestones, form from the accumulation of plant or animal debris. Sedimentary rocks are important to the Earth’s history. As layers of sediments are accumulated, they carry with them the records of the environment's nature at the time the sediments were deposited. These layers are called strata. Fossils are only found in sedimentary rocks. Metamorphic rocks are rocks that form from the transformation of the pre-existing rocks (igneous, sedimentary, or metamorphic rocks) through the process of metamorphism. Metamorphism can involve changes in the physical and chemical properties of the rocks in response to heat, pressure (stress), and chemical agents. It takes place when the physical and chemical environment of the parent rock is changed. The following conditions induce metamorphism of rocks: a. Heat – it is the major factor that triggers metamorphism. It causes a chemical reaction that results in recrystallization of minerals present in rocks, so new minerals are formed. Heat energy may be caused by the intrusion of magma that rises from the mantle. FEU High School Earth and Life Science Module 3| AY 24-25 b. Pressure (stress) – increases with depth. Buried rocks are subjected to enormous pressure that causes the spaces between mineral grains to close resulting in a more compact and denser rock. It also results to recrystallization and formation of new minerals. c. Chemical agent – water, some volatile substances, and carbon dioxide act as catalysts in the recrystallization of minerals. In contact metamorphism, heat acts as the main factor. It occurs when a parent or pre-existing rocks get in contact with a heat source such as magma. It occurs on a small scale, near intruding magma and creates non-foliated metamorphic rocks. In regional metamorphism, pressure acts as the main factor. It occurs in areas that have undergone deformation during an orogenic event resulting in mountain belts. It usually occurs on a large scale and creates foliated metamorphic rocks. FEU High School Earth and Life Science Module 3| AY 24-25 The Rock Cycle Rocks undergo processes that transform them from one type to another (igneous, sedimentary, and metamorphic). The processes that these rocks undergo would dictate the type they will transform to and is a factor of the environment where the rocks are located. The rock cycle illustrates and describes how geologic processes occurring both at the surface and underneath the Earth’s surface can continuously transform or change a rock from one type to another (Figure 2.33) The melting of rocks occurs within the Earth’s crust and the upper mantle because of extreme heat. Magma rises to the surface because it is less dense than the surrounding rocks. Volcanic activities expose the magma to the surface as lava. Eventually, lava cools and solidifies through a process called crystallization or solidification. Molten rocks can either solidify beneath the surface or on the surface during a volcanic eruption. The solidified molten rock becomes igneous rocks. Through uplifting, an igneous rock is exposed to the surface. Due to the influence of the atmosphere, this rock disintegrates or undergoes weathering. The rocks become loose soil that can easily move downslope due FEU High School Earth and Life Science Module 3| AY 24-25 to gravity and other agents of erosion such as water, wind, waves, or glaciers. The particles are transformed into dissolved materials called sediments. Sediments are deposited in oceans, rivers, and other bodies of water. They undergo lithification through compaction and cementation and transform into sedimentary rocks. Sedimentary rocks may be deeply buried and subjected to intense pressure (stress) and heat. Due to the change in temperature and pressure, this type of rock may undergo physical or chemical changes and be transformed into metamorphic rocks. If a metamorphic rock is exposed to extreme heat and pressure deep down the Earth’s mantle, it may melt, form magma, and the cycle begins again. However, it takes time for the changes to happen. Rocks do not necessarily change according to the cycle. Igneous, sedimentary, and metamorphic rocks turn into sedimentary rock when exposed to weathering and erosion. The same is true when they remain buried underground and are subjected to intense heat and pressure, they change to metamorphic rocks. Likewise, if all three types of rocks go to the mantle, they melt and turn into igneous rocks when cooled. FEU High School Earth and Life Science Module 3| AY 24-25 REFERENCES BOOKS Religioso, T. F., Vengco, L. G. (2018). You and the Natural World: Earth and Life Science. Phoenix Publishing House, Inc. Guzman-Genuino, R. M., Refran, J. C., Tolentino, P. L. M. (2016). Earth and Life Science. Vibal Group Inc. Briones, J. A., et. al (2016). Earth and Life Science: Knowing and Understanding Nature. Abiva Publishing House, Inc. Duyanen, J. P., Ortiz-Andaya, M. (2016). Earth and Life Sciences for Senior High School. C & E Publishing, Inc. WEBSITES Rock Cycle Interactive. https://www.learner.org/series/interactive-rock-cycle/ What are Minerals? https://geology.com/minerals/what-is-a-mineral.shtml How do Rocks Undergo Change? http://www.classzone.com/books/earth_science/terc/content/investigations/es0602/es0602page01. cfm?chapter_no=06 The Rock Cycle. http://www.phschool.com/atschool/phsciexp/active_art/rock_cycle/ Eifert, T. L. (n.d.). Mineral Lusters. http://www.geologyfortoday.com/mineral-lusters.html VIDEOS Pop, Homeschool. (2020, February 26). Rocks for Kids. [Video file]. Retrieved from https://youtu.be/ty2Za-O9h6w Bieler, M. (2018, February 26). Mineral Identification.... Cleavage vs. Fracture. [Video file]. Retrieved from https://youtu.be/1SGC3VBQZY0 Sammartano, M. (2015, February 8). Rocks and Minerals. [Video file]. Retrieved from https://www.youtube.com/watch?v=ZkHp_nnU9DY&feature=youtu.be Sammartano, M. (2015, January 27). Identifying Minerals. [Video file]. Retrieved from https://youtu.be/32NG9aeZ7_c Sammartano, M. (2013, February 3). Rock Cycle. [Video file]. Retrieved from https://www.youtube.com/watch?v=BgJ74KKZyD4&feature=youtu.be Sammartano, M. (2013, January 24). What is a Metamorphic Rock? [Video file]. Retrieved from https://youtu.be/1oQ1J0w3x0o Heeke, S. (2013, January 22). Mineral Hardness Test. [Video file]. Retrieved from https://youtu.be/R-bw7_u3gSQ Sammartano, M. (2013, January 20). What is a Sedimentary Rock? {Video file]. Retrieved from https://youtu.be/Etu9BWbuDlY Sammartano, M. (2013, January 15). What is an Igneous Rock? [Video file]. Retrieved from https://youtu.be/aCnAF1Opt8M Sammartano, M. (2011, January 11). A Brief Introduction to Minerals. [Video file]. Retrieved from https://www.youtube.com/watch?v=8a7p1NFn64s&feature=youtu.be FEU High School Earth and Life Science Module 3| AY 24-25