Chapter 3: Minerals

Concepts:

1. What is an element? A cation? An anion? How does an atom become an anion?

   • Element: A pure substance consisting of one type of atom, characterized by the number of protons in its nucleus (atomic number). Examples: oxygen (O), hydrogen (H), carbon (C).

   • Cation: A positively charged ion, formed when an atom loses one or more electrons.

   • Anion: A negatively charged ion, formed when an atom gains one or more electrons.

   • How an atom becomes an anion: An atom becomes an anion by gaining one or more electrons, which results in a negative charge because the number of electrons exceeds the number of protons.

2. What is the most abundant element in the Earth?

   • Oxygen (O) is the most abundant element in the Earth’s crust, making up about 46% of its weight. Silicon (Si) is the second most abundant.

3. What is a mineral?

   • A mineral is a naturally occurring, inorganic solid with a specific chemical composition and a crystalline structure. Examples: quartz, feldspar, and calcite.

4. What types of bonds are there? Why are bond types important? What effects do they have on a mineral?

   • Types of bonds:

     • Ionic bond: Electrons are transferred between atoms, creating charged ions that are attracted to each other (e.g., sodium chloride).

     • Covalent bond: Electrons are shared between atoms (e.g., diamonds).

     • Metallic bond: Electrons move freely between metal atoms (e.g., copper).

     • Hydrogen bond: Weak bond between a hydrogen atom and an electronegative atom like oxygen or nitrogen (e.g., water molecules).

   • Importance of bond types: The type of bond affects the mineral's hardness, cleavage, electrical conductivity, and other physical properties.

5. What controls the properties of a mineral, the cation or the anion? Why?

   • The anion controls most of the properties of a mineral. This is because the anion often determines the mineral's overall structure and its chemical composition. For example, in quartz (SiO₂), the silicon-oxygen bonding governs its properties.

6. How do minerals form? How is each process different?

   • Minerals form through several processes:

     • Crystallization from magma: Minerals form as hot magma cools and solidifies, allowing atoms to arrange into crystalline structures.

     • Evaporation: When water evaporates, it can leave behind minerals that had been dissolved in the water (e.g., salt deposits).

     • Metamorphism: Minerals can form when pre-existing minerals are subjected to high pressure and temperature, changing their structure.

     • Precipitation from solutions: When the concentration of certain elements in a solution becomes too high, minerals precipitate out (e.g., calcite in caves).

7. What is the most abundant rock-forming mineral group? What are some examples?

   • The most abundant rock-forming mineral group is the silicates. Examples include:

     • Quartz (SiO₂)

     • Feldspar (KAlSi₃O₈)

     • Mica (muscovite, biotite)

8. What are the physical/chemical properties of minerals? How are they used? What is Mohs Hardness scale? Are all of them equally helpful in mineral identification? Why or why not?

   • Physical properties:

     • Hardness (resistance to scratching)

     • Color

     • Streak (color of the powdered mineral)

     • Luster (how light reflects off the surface)

     • Cleavage (how a mineral breaks along planes of weakness)

     • Fracture (breaks in an irregular pattern)

   • Chemical properties:

     • Reactivity with acids (e.g., calcite reacts with hydrochloric acid).

   • Mohs Hardness Scale: A scale from 1 (talc) to 10 (diamond), used to measure the hardness of a mineral.

   • Are all properties equally helpful? No, not all properties are equally helpful for mineral identification. For example, color can be misleading because different minerals may appear similar in color but have different properties like hardness or streak.

9. What are the different types of mineral classes? How are they defined? Which group is the most abundant on Earth?

   • Mineral classes are defined by their chemical composition. The main classes include:

     • Silicates: Minerals that contain silicon and oxygen (e.g., quartz, feldspar).

     • Oxides: Minerals composed of oxygen and a metal (e.g., hematite, magnetite).

     • Carbonates: Contain the carbonate ion (CO₃) (e.g., calcite).

     • Sulfates: Contain the sulfate ion (SO₄) (e.g., gypsum).

     • Sulfides: Contain sulfur (e.g., pyrite).

     • Halides: Contain halogen elements (e.g., halite, fluorite).

   • The silicates are the most abundant group on Earth.

10. What is a rock?

• A rock is a naturally occurring solid composed of one or more minerals, mineraloids, or organic materials. Rocks are classified based on their formation process, such as igneous, sedimentary, or metamorphic.