EONS LEARNING

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      • Periodic Table
      • Common Ion Sheet
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    • Unit 1: Beginning Chemistry >
      • Lesson 1: The Atom >
        • What is an Atom?
        • The Structure of Atoms
        • The Periodic Table
        • Modeling Atoms
      • Lesson 2: Chemical Bonding >
        • Why Do Atoms Form Bonds?
        • Ionic Bonding
        • Covalent Bonding
        • Intermolecular Attraction
      • Lesson 3: Chemical Nomenclature >
        • Octet Rule
        • Ionic Compounds
        • Covalent Molecules
      • Lesson 4: Molecular Molecules >
        • Modeling Ionic Compounds
        • Modeling Covalent Molecules
      • Lesson 5: States of Matter >
        • States of Matter
        • Phase Changes
      • Lesson 6: Density >
        • What is Density?
        • Calculating Density
      • Lesson 7: Thermodynamics >
        • Temperature
        • Heat
        • Gas Laws
      • Lesson 8: Solution Chemistry >
        • Diffusion
        • Solutions and Molarity
        • Semi-Permeable Membranes
      • Lesson 9: Thermal Expansion >
        • Thermal Expansion
    • Unit 2: Earth Science >
      • Lesson 10: Earth at a Glance >
        • Perspective
        • Maps
      • Lesson 11: Layers of the Earth >
        • Layers of the Earth
      • Lesson 12: Plate Tectonics >
        • Plate Tectonics
      • Lesson 13: Rocks and Minerals >
        • Rocks and Minerals
      • Lesson 14: Particle Sorting >
        • Differentiation
        • Deposition of Sediment
      • Lesson 15: The Atmosphere >
        • Composition of the Atmosphere
        • Layers of the Atmosphere
        • Change Over Time
        • Atmospheric Disruption
    • Unit 3: The Cell >
      • Lesson 16: Life >
        • What is Life?
        • Structural Hierarchy of Living Things
      • Lesson 17: Biochemistry >
        • Intro to Biochemistry
        • Water
        • Micromolecules
        • Energy, Carbohydrates, Lipids
        • Protein and Nucleic Acid
      • Lesson 18: Cells >
        • What are Cells?
        • Microscopy
        • Plant and Animal Cells
      • Lesson 19: Membrane Transport >
        • A Special Environment
        • The Structure of Membranes
        • Membrane Transport
      • Lesson 20: Energy and Cell Respiration >
        • Energy in Biology
        • Energy Diagrams
        • Glycolysis and Anaerobic Respiration
        • Aerobic Cellular Respiration
      • Lesson 21: Photosynthesis >
        • Plants Get Energy From The Sun
        • Photosynthesis Process
        • Energy, Ecosystems, and the Environment
    • Unit 4: Anatomy and Physiology >
      • Lesson 22: The Human Body >
        • What Are Bodies Made Of?
        • What Do Bodies Do?
      • Lesson 23: The Nervous System >
        • The Nervous System
        • Neuronal Communication
        • The Central Nervous System
      • Lesson 24: The Endocrine System >
        • The Endocrine System
        • Hormones
        • Hormones, Puberty, and Reproduction
      • Lesson 25: The Integumentary System >
        • The Integumentary System
      • Lesson 26: The Musculoskeletal System >
        • The Skeletal System
        • The Muscular System
        • Anatomy Of The Musculoskeletal System
      • Lesson 27: The Cardiovascular System >
        • Blood and Blood Vessels
        • The Heart
      • Lesson 28: The Respiratory System >
        • The Respiratory System
      • Lesson 29: The Digestive System >
        • The Digestive System
        • Nutrition
      • Lesson 30: The Excretory System >
        • The Excretory System
      • Lesson 31: The Immune System >
        • Disease and Infection
        • Immunity
    • Units 5-6 Coming Soon
  • Workbench
    • Unit 1 >
      • EIS >
        • Lesson 1: Atoms
        • Lesson 2: Chemical Bonding
        • Lesson 3: Chemical Nomenclature
        • Lesson 4: Molecular Models
        • Lesson 5: States of Matter
        • Lesson 6: Density
        • Lesson 7: Thermodynamics
        • Lesson 8: Solution Chemistry
        • Lesson 9: Thermal Expansion
      • Unit 1: Project
      • Unit 1: Exam Review
      • Unit 1: Exam
    • Unit 2 >
      • EIS >
        • Lesson 10: Earth at a Glance
        • Lesson 11: Layers of the Earth
        • Lesson 12: Plate Tectonics
        • Lesson 13: Rocks and Minerals
        • Lesson 14: Particle Sorting
        • Lesson 15: The Atmosphere
      • Unit 2: Project
      • Unit 2: Exam Review
      • Unit 2: Exam
    • Unit 3 >
      • EIS >
        • Lesson 16: Life
        • Lesson 17: Biochemsitry
        • Lesson 18: Cells
        • Lesson 19: Membrane Transport
        • Lesson 20: Energy and Cell Respiration
        • Lesson 21: Photosynthesis
      • Unit 3: Project
      • Unit 3: Exam Review
      • Unit 3: Exam
    • Unit 4 >
      • EIS >
        • 22: The Human Body
        • 23: The Nervous System
        • 24: The Endocrine System
        • 25: The Integumentary System
        • 26: The Musculoskeletal System
        • 27: The Cardiovascular System
        • 28: The Respiratory System
        • 29: The Digestive System
        • 30: The Excretory System
        • 31: The Immune System
      • Unit 4 Project
      • Unit 4 Exam Review
      • Unit 4 Exam
    • Units 5-6 Coming Soon
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  • Home
  • About Us
  • Classroom
    • Resources >
      • Study Skills
      • Periodic Table
      • Common Ion Sheet
      • The Scientific Method
      • Doing Background Research
    • Introduction and Course Philosophy
    • Unit 1: Beginning Chemistry >
      • Lesson 1: The Atom >
        • What is an Atom?
        • The Structure of Atoms
        • The Periodic Table
        • Modeling Atoms
      • Lesson 2: Chemical Bonding >
        • Why Do Atoms Form Bonds?
        • Ionic Bonding
        • Covalent Bonding
        • Intermolecular Attraction
      • Lesson 3: Chemical Nomenclature >
        • Octet Rule
        • Ionic Compounds
        • Covalent Molecules
      • Lesson 4: Molecular Molecules >
        • Modeling Ionic Compounds
        • Modeling Covalent Molecules
      • Lesson 5: States of Matter >
        • States of Matter
        • Phase Changes
      • Lesson 6: Density >
        • What is Density?
        • Calculating Density
      • Lesson 7: Thermodynamics >
        • Temperature
        • Heat
        • Gas Laws
      • Lesson 8: Solution Chemistry >
        • Diffusion
        • Solutions and Molarity
        • Semi-Permeable Membranes
      • Lesson 9: Thermal Expansion >
        • Thermal Expansion
    • Unit 2: Earth Science >
      • Lesson 10: Earth at a Glance >
        • Perspective
        • Maps
      • Lesson 11: Layers of the Earth >
        • Layers of the Earth
      • Lesson 12: Plate Tectonics >
        • Plate Tectonics
      • Lesson 13: Rocks and Minerals >
        • Rocks and Minerals
      • Lesson 14: Particle Sorting >
        • Differentiation
        • Deposition of Sediment
      • Lesson 15: The Atmosphere >
        • Composition of the Atmosphere
        • Layers of the Atmosphere
        • Change Over Time
        • Atmospheric Disruption
    • Unit 3: The Cell >
      • Lesson 16: Life >
        • What is Life?
        • Structural Hierarchy of Living Things
      • Lesson 17: Biochemistry >
        • Intro to Biochemistry
        • Water
        • Micromolecules
        • Energy, Carbohydrates, Lipids
        • Protein and Nucleic Acid
      • Lesson 18: Cells >
        • What are Cells?
        • Microscopy
        • Plant and Animal Cells
      • Lesson 19: Membrane Transport >
        • A Special Environment
        • The Structure of Membranes
        • Membrane Transport
      • Lesson 20: Energy and Cell Respiration >
        • Energy in Biology
        • Energy Diagrams
        • Glycolysis and Anaerobic Respiration
        • Aerobic Cellular Respiration
      • Lesson 21: Photosynthesis >
        • Plants Get Energy From The Sun
        • Photosynthesis Process
        • Energy, Ecosystems, and the Environment
    • Unit 4: Anatomy and Physiology >
      • Lesson 22: The Human Body >
        • What Are Bodies Made Of?
        • What Do Bodies Do?
      • Lesson 23: The Nervous System >
        • The Nervous System
        • Neuronal Communication
        • The Central Nervous System
      • Lesson 24: The Endocrine System >
        • The Endocrine System
        • Hormones
        • Hormones, Puberty, and Reproduction
      • Lesson 25: The Integumentary System >
        • The Integumentary System
      • Lesson 26: The Musculoskeletal System >
        • The Skeletal System
        • The Muscular System
        • Anatomy Of The Musculoskeletal System
      • Lesson 27: The Cardiovascular System >
        • Blood and Blood Vessels
        • The Heart
      • Lesson 28: The Respiratory System >
        • The Respiratory System
      • Lesson 29: The Digestive System >
        • The Digestive System
        • Nutrition
      • Lesson 30: The Excretory System >
        • The Excretory System
      • Lesson 31: The Immune System >
        • Disease and Infection
        • Immunity
    • Units 5-6 Coming Soon
  • Workbench
    • Unit 1 >
      • EIS >
        • Lesson 1: Atoms
        • Lesson 2: Chemical Bonding
        • Lesson 3: Chemical Nomenclature
        • Lesson 4: Molecular Models
        • Lesson 5: States of Matter
        • Lesson 6: Density
        • Lesson 7: Thermodynamics
        • Lesson 8: Solution Chemistry
        • Lesson 9: Thermal Expansion
      • Unit 1: Project
      • Unit 1: Exam Review
      • Unit 1: Exam
    • Unit 2 >
      • EIS >
        • Lesson 10: Earth at a Glance
        • Lesson 11: Layers of the Earth
        • Lesson 12: Plate Tectonics
        • Lesson 13: Rocks and Minerals
        • Lesson 14: Particle Sorting
        • Lesson 15: The Atmosphere
      • Unit 2: Project
      • Unit 2: Exam Review
      • Unit 2: Exam
    • Unit 3 >
      • EIS >
        • Lesson 16: Life
        • Lesson 17: Biochemsitry
        • Lesson 18: Cells
        • Lesson 19: Membrane Transport
        • Lesson 20: Energy and Cell Respiration
        • Lesson 21: Photosynthesis
      • Unit 3: Project
      • Unit 3: Exam Review
      • Unit 3: Exam
    • Unit 4 >
      • EIS >
        • 22: The Human Body
        • 23: The Nervous System
        • 24: The Endocrine System
        • 25: The Integumentary System
        • 26: The Musculoskeletal System
        • 27: The Cardiovascular System
        • 28: The Respiratory System
        • 29: The Digestive System
        • 30: The Excretory System
        • 31: The Immune System
      • Unit 4 Project
      • Unit 4 Exam Review
      • Unit 4 Exam
    • Units 5-6 Coming Soon
  • Donate

Rocks and Minerals

Rocks. They’re everywhere. They’re gorgeous. And they are the subject of this lesson. Before we get into the details, just enjoy this beautiful ode to the majesty of rocks:
#GetOutInNature

Rocks and minerals are found all around us, in the land beneath our feet, the countertops in our kitchen, and even in the hardware of our electronics. They have a significant influence on our lives, but how much do we really know about them?

What are Minerals?

Let’s begin by clarifying something: Rocks and minerals are not the same thing. Minerals are naturally occurring crystalline structures of inorganic compounds. Each of these crystals is made up of a single, pure substance—often ionic compounds, and sometimes covalent molecules—and therefore have distinct physical and chemical properties depending on the exact compound or molecule that makes them up.

One example of a common mineral is halite, which is just the crystalline structure of NaCl—table salt.
Picture
The Salt Flats in Utah are made up mainly of halite:
Picture
Another common mineral is quartz, which is the crystalline structure of silicon dioxide (SiO₂):
Picture
Picture

What Are Rocks?

Rocks, on the other hand, are formed from combinations of minerals and organic compounds. Although there are certain classifications of rock that tend to contain similar substances, the exact composition of the rock and the proportions of the various substances that it contains will vary based on where and how that rock formed.

Granite, for instance, contains between 10 and 50 percent quartz and can sometimes include mica and hornblende.
Picture
Granite, which is often used in countertops, contains different amounts of minerals depending on where it formed.
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El Capitan-- one of nature's largest granite monolith's at about 3,000 feet tall is both beautiful and a popular objective for rock climbers.

How do We Classify Rocks?

Since we can’t define the chemical nature of a rock exactly, like we can describe minerals by their chemical structures, scientists have turned to classification to make understanding the composition of rocks easier. There are 3 main classes of rocks, which are defined by how they’re formed: igneous, sedimentary, and metamorphic. We can also put rocks into more specific categories like “granite,” which is more closely related to the composition of the rock, but we won’t worry about getting that detailed in this class.

Igneous rocks form from magma bubbled up from the mantle below Earth’s crust, and then cooled. Rapid cooling results in many small crystals that cannot be seen with the naked eye, so the rock looks and feels smooth. Obsidian
, shown below, is a good example of an igneous rock.
Picture
Black obsidian, an igneous rock
Gas bubbles can also be trapped in magma during cooling (remember that carbon dioxide is formed from the recycling of old, organic crust). Pumice, another type of igneous rock, gets its porous appearance from these gas bubbles. Because of its structure, pumice is less dense than water and floats in the liquid. 
Picture
Pumice, an igneous rock with trapped gas bubbles.

​Sedimentary rocks form from, as the name suggests, sediments. Sediment is basically a fancy word for dirt: A mixture of ground up old rock and decaying organic material. Sedimentary  rocks can be further classified based on their composition. Clastic sedimentary rocks are formed from the mechanical weathering debris while chemical sedimentary rocks are formed from precipitates of dissolved materials. These rocks are often easy to spot because of their “chunkiness,” meaning that you can actually see the broken up old chunks of rocks and minerals, as in granite (shown above) or hematite:
Picture
Hematite, a sedimentary rock rich in iron

​Sometimes, sedimentary rocks are made up of smaller sediment particles that appear deceptively smooth, making these sedimentary rocks more difficult to spot. One example is shale:
Picture
Shale forms from silt, clay, and mud, so it has a smooth appearance, unlike many other sedimentary rocks.

​Metamorphic rocks are rocks that have been changed (hence, metamorphic, like how a caterpillar changes into a butterfly by metamorphosis) by intense heat and pressure. These conditions are often found deep underground. Rocks can also be changed by chemical processes. Any rock can become a metamorphic rock given enough heat and pressure, including sedimentary, igneous, and other, older, metamorphic rocks.
Picture
Metamorphic rocks can typically be recognized because of their banding pattern, which forms as a result of different layers of rock being forced together under pressure:
Picture
These are good classifications to understand. But, they aren’t fixed. Just like any rock can become metamorphic under enough heat and pressure, rocks can become sediment if they are crushed enough and, eventually, igneous as Earth’s crust becomes recycled due to plate tectonics. This cheesy video will explain more:
​

​Cool, right? Which brings us back to a couple of important ideas that we’ve brought up before: First, that categories aren’t always perfect, and the real world is often more complex than our simple categories account for. Second, even things that seem fixed, like rocks, or the surface of the earth, are constantly changing. They’re just doing it slowly.

Density of Rocks and Minerals

The density of various rocks and minerals is dependent on their composition and formation. It can be hard to predict the density of a rock even if you know what type it is. This is because different amounts of minerals can go into it depending on where it was formed, and each of these minerals has different densities. Also, like with pumice, gas bubbles can get trapped in the rock, giving them very low density. For this reason, the most reliable way to determine the density of a specific rock is to measure it. Just like we did in chemistry, we can measure the volume of the rock by fluid displacement (sinking it in water and seeing how much the volume changes) and the mass of the rock using a scale. We can then calculate density with the equation d = m/V.

In the case of minerals, specific gravity is a useful feature for identification, as each mineral has a fairly consistent density. The specific gravity of something is just the density of one thing relative to the density of another thing (a ratio). Commonly, we use the specific gravity relative to water, which has a density of 1 g/mL. In this case, specific gravity is the exact same as density (because we’re just dividing by 1). Saying that specific gravity is helpful for identifying minerals is very similar to saying that density is helpful for identifying unknown metals, like we practiced in the Chemistry unit. This video demonstrates the usefulness of specific gravity for identifying minerals well:
​

​Metallic minerals generally have higher specific gravities than non-metallic minerals, as they contain heavier metal elements and are held together by stronger intermolecular attractions: ionic bonds. Non-metallic minerals are held together by the relatively weaker coordinate covalent bonds, which are still strong, but not quite as strong. So, molecules are pulled tighter together in metallic minerals, making them more dense.

It’s harder to come up with a general trend for the density of rocks, because there are a lot of exceptions. But, in general, sedimentary rocks tend to be the least dense, because they are basically loosely packed dirt, igneous rocks are of a medium density, and metamorphic rocks are of the highest density because the contents have been pushed together under pressure. This should make sense based on what you have learned about how different rocks are formed. You should also recognize that there are many exceptions, such as pumice being a very lightweight rock due to the trapped gases.

Summary

You should understand:
  • The difference between rocks and minerals.
  • The difference between igneous, sedimentary, and metamorphic rocks in terms of their general appearance and how they are formed.
  • How to calculate density of a rock or mineral.
  • How to identify an unknown mineral from its specific gravity and a chart of known specific gravities.
  • The general trends in density of rocks and minerals:
    • Metallic minerals are generally more dense than nonmetallic minerals.
    • With many exceptions, metamorphic rocks are generally more dense than igneous rocks, which are generally more dense than sedimentary rocks.

Learning Activity

Picture
Lesson 14: Particle Sorting
Lesson 13: rocks and minerals eis

Content contributors: Suzanne Xu, Emma Moulton
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