Ch. 3 - Matter and Minerals

Class: GEOL-101

Notes:

3.1 Minerals: Building Blocks of Rocks

List and describe the main characteristics that an Earth material must possess to be considered a mineral.

Geologic Definitions

Presentation content:

Geologic definition of Mineral

• Naturally occurring
• Generally inorganic
• Solid substance
• Orderly crystalline structure
• Definite chemical composition
  • (that allows for some variation)

Definition of a Rock

• A solid mass of aggregated minerals or mineral-like matter that occurs naturally

Notes from the lecture:

• Corals biominerilize a carbonate skeleton, some companies dedicate to this
• Are they minerals?
  • Gold
    • Yes it is a mineral
  • Liquid Water
    • No it is not a mineral (not a crystalline structure)
  • Ice
    • Yes it is a mineral
  • Coal
    • Not a mineral (its organic)
    • Derived from organic matter, heated and pressurized and turned into coal
    • If you continue to heat coal, eventually all that is left is the carbon, which you can turn into graphite, later you can turn it into diamond.
• A rock is a combination of different minerals
  • Example: Granite (rock) consist of 3 different minerals
    • Quartz (mineral)
    • Horrblende (mineral)
    • Feldspar (mineral)

3.2 Atoms: Building Blocks of Minerals

Compare and contrast the three primary particles contained in atoms.

Atoms

Presentation content:

• Smallest particles of matter that cannot be chemically split
• Composed of:
  • Protons: charge of +1
  • Neutrons: charge of 0
  • Surrounded by electrons: charge of –1
• Electrons exist as a cloud of negative charges surrounding the nucleus of protons and neutrons, occurring in regions called principal shells.
• The outermost shell contains valence electrons, which interact with other atoms to form chemical bonds.

Notes from the lecture:

• Protons and Neutrons both have mass and weight, but only protons have positive charge. Electrons are significantly smaller than any proton or neutron.
• The outermost shell that contains electrons is what we call valance electrons

Atomic Numbers and Elements

Presentation content:

• Atomic Number
  • The number of protons in the nucleus of an atom
  • Determines the atom’s chemical nature
• Element
  • A group of the same kind of atoms
  • Approximately 90 natural elements and several synthesized in a laboratory
  • Organized in the periodic table so that those with similar properties line up
  • Most elements join with other elements to form chemical compounds

Notes from the lecture:

• The periodic table is largely organized by its atomic number
• Elements are characterized by atoms that have similar structure
• Synthesized in the laboratory are very unstable elements
• Elements join together to form chemical compounds
• Elements on the left hand side tend to lose electrons
• Elements on the top right hand side tend to receive electrons
• Atoms want to have 8 electrons in the outer shell to be stable

3.3 How Atoms Bond to Form Minerals

Distinguish among ionic bonds, covalent bonds, and metallic bonds and explain how they form minerals.

Chemical Bonding

Presentation content:

• Transferring or sharing electrons allows atoms to attain a full valence shell of electrons
  • Lowers total energy of bonded atoms
  • Makes them more stable
• Octet Rule
  • Atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons
• Most minerals are chemical compounds of composed of atoms of two or more elements.

Notes from the lecture:

• Sodium and Chlorine tend to bond together, they complete each others electrons
• All minerals consist of more than one element
  • There are exceptions: gold, silver copper - natural metals

Ionic bonding and Covalent Bonding

Presentation content:

• Ionic Bonding

  • Atoms gain or lose outermost (valence) electrons to form ions.
  • Driven by the attraction of oppositely charged ions to one another.

  

  • Sodium loses an electron
  • Chlorine gains an electron

• Covalent Bonding

  • Atoms share one or more valence electrons
  • Attraction between oppositely charged particles:
    • Positively charged protons
    • Negatively charged electrons
  • Covalent bonds are the strongest atomic bonds

  

Notes from the lecture:

• Two hydrogen atoms bond together in order to create an H₂ molecule

Metallic and Hybrid Bonds

Presentation content:

• Metallic Bonding

  • Valence electrons are free to migrate among atoms
  • Accounts for the high electrical conductivity of metals

• Hybrid Bonds

  • Many chemical bonds are actually hybrids that exhibit some degree of electron sharing and some degree of electron transfer.
  • Silicate minerals are comprised of hybrid bonds

Notes from the lecture:

• Metallic bond: Elements that are very good electrical conductors
• Hybrid Bond: Some degree of electron transfer

Precipitation of Mineral Matter

Presentation content:

• Ions dissolved in an aqueous solution reach saturation and start forming crystalline solids
  • Drop in temperature or water lost through evaporation brings the solution closer to saturation
  • Once saturation is reached, ions begin to bond, forming crystalline solids
  • Evaporite deposits (salts)
• Minerals can precipitate from slowly moving groundwater filling fractures and voids.
  • Geodes

Notes from the lecture:

• One way is precipitation
  • Supersaturate a fluid with sugar, and some sugar crystals start to actually precipitate
• Geodes are consisted of a mineral called Quartz
  • A fluid is saturate, as it changes its temperature, the fluid is precipitated and forms crystals
  • Using all available ions in that solution
  • Continue to evaporate water = increase concentration

Crystallization and Deposition

Presentation content:

• Crystallization of Molten Rock

  • Similar to water freezing
  • When the magma is hot, the atoms are mobile, when the magma cools, the atoms slow and begin to chemically combine.
  • Generates a mosaic of intergrown crystals

• Deposition as a Result of Biological Processes

  • Marine organisms use calcium or silica from seawater and secrete external skeletons composed of calcium carbonate (CaCO₃) or silica.
    • Corals and mollusks use Ca
    • Diatoms and radiolarians use Si

Notes from the lecture:

• In this case we are actually cooling materials

  • Magma is usually full of Iron, Magnesium, Silica, Oxygen

• As it starts to cool, atoms start locking into place, so they start forming inter-locking crystals

  • You can see it in the form of heterogeneous crystals

• Oysters have a shell

  • Taking nutrients out of the water
  • Using these ions to grow their shell

3.4 Properties of Minerals

List and describe the properties used in mineral identification.

Properties of Minerals

Presentation content:

• Definite crystalline structure and chemical composition of minerals give them unique physical and chemical properties.
• Primary diagnostic properties
  • Determined by observation or performing a simple test
  • Several physical properties are used to identify hand samples of minerals.

Notes from the lecture:

• There are 4000 different minerals
• It is not easy to determine what type of minerals we are in front of
• We use tests to look at their different properties
  • Crystal orientations
  • Crystal habits
  • etc.

Optical Properties

Presentation content:

• Luster - Appearance of a mineral in reflected light
• Two basic categories:
  • Metallic
  • Nonmetallic: Glassy, Dull, Pearly, Silky, Greasy
• Streak
  • Color of a mineral in its powdered form
  • Although a mineral’s color may vary, its streak is usually consistent in color.
  • Determined by rubbing it across a porcelain plate
• Ability to Transmit Light
  • Opaque
  • Translucent
  • Transparent
• Color
  • Often highly variable due to impurities or slight changes in mineral chemistry

Notes from the lecture:

• Powder from streak is a mineral
  • Streak is always the same color, it is very reliable
• Color is not very reliable since some come in a variety of colors

Crystal Shape, or Habit

Presentation content:

• Characteristic shape of a crystal or aggregate of crystals
• Minerals tend to have one common crystal shape, but a few have two or more characteristic shapes.

Notes from the lecture:

• A little bit more reliable
• Minerals tend to follow crystal habits
• Example:
  • Pyrite
    • Specific geometry, right angles, cube-like shape of crystals
• Very valuable indicator of which mineral it is
  • Not always possible, and there are very small crystals

Mineral Strength

Presentation content:

• How easily minerals break or deform under stress
• Hardness
  • Resistance of a mineral to abrasion or scratching
  • All minerals are compared to a standard scale called the Mohs scale of hardness.

• Cleavage
  • Tendency to break (cleave) along planes of weak bonding. Producing smooth, flat surfaces
  • Described by:
    • Number of planes
    • Angles between adjacent planes
    • Resulting geometric shapes

• Fracture

  • Minerals with equally strong bonds have an absence of cleavage
    • Irregular fractures
      • Not easy to find a pattern in their wreckage
    • Conchoidal fractures
      • Patterns that resemble when glass or obsidian breaks
    • Splintery fractures
      • Thin, sharp, and elongated, resembling splinters of wood
    • Fibrous fractures
      • Produces a long, thread-like appearance.

• Tenacity: The mineral’s resistance to breaking or deforming

  • Brittle minerals (ionic bonds) will shatter into small pieces.
  • Malleable minerals (metallic bonds) are easily hammered into different shapes.
  • Sectile minerals, such as gypsum and talc, can be cut into thin shavings.
  • Elastic minerals, such as the micas, will bend and snap back to their original shape.

Notes from the lecture:

• Hardness
  • Need a lab for testing this
  • Simply saying which minerals are harder than which others
  • If it does not scratch, it is probable that it is a diamond
  • Gypsum tends to scratch with your fingernails
• Cleavage
  • Some minerals break apart in certain forms
  • Some break into little cubes
  • In certain minerals it is not a reliable tool
  • Different angles are very valuable in terms of identifying minerals
• Fracture
  • Quartz does not exhibit cleavage
  • It breaks up into a number of different pieces
  • Most minerals do have cleavage
• Tenacity
  • Blending in certain way won't break the mineral

Density and Specific Gravity

Presentation content:

• Density is defined as mass per unit volume
• Specific gravity:
  • The ratio of the weight of a mineral to the weight of an equal volume of water
  • Most have a specific gravity between 2 and 3
  • The specific gravity of galena (PbS) is 7.5 and 24 karat gold is 20!

Notes from the lecture:

• There are lots of minerals with similar density - not a very reliable method
• Specific gravity:
  • Answer how much more heavy is it than 1 cm^3 of water

Other Properties of Minerals

Presentation content:

• Taste - Halite tastes like salt
• Feel - Talc feels soapy, graphite feels greasy
• Stinky streak - Sulfur-bearing minerals have streaks that smell like rotten eggs
• Magnetism - Magnets pick up magnetite, lodestone is a natural magnet
• Double refraction - Transparent calcite
• Effervescence - Carbonates fizz in reaction to dilute hydrochloric acid

Notes from the lecture:

• Double refraction is exclusive to Calcite crystals
• Carbonates react to hydrochloric acid

3.5 Mineral Structures and Compositions

Distinguish between compositional and structural variations in minerals and provide one example of each.

Mineral Structures - Unit cells

Presentation content:

• All mineral samples are crystals or crystalline solids
  • Any natural solid with orderly, repeating internal structures.
• Mineral Structures
  • Atomic arrangement that results in the basic building blocks of a mineral crystal, called unit cells.

• Unit cells combine to form mineral crystals
  • Two minerals can be constructed of geometrically similar building blocks and exhibit different crystal forms.
  • Examples of minerals with cubic unit cells include:
    • Fluorite – crystals are cubes
    • Magnetite – crystals are octahedrons
    • Garnets – crystals are dodecahedrons

Notes from the lecture:

• Halite forms little cubes, this is because of the called unit cells
• Unit cells are mimicking the cleavage of the mineral

Steno's Law

Presentation content:

• Law of Constancy of Interfacial Angles
  • Regardless of crystal size, the angles between equivalent crystal faces of the same mineral are consistent.
  • Observation first made by Nicolas Steno in 1669

Notes from the lecture:

• Take a halite crystal, smash it, it will break into little cubes
• This is because of its structure
• Some tools are subjective, some are limited by the sample, some are reliable
• We can use X-ray reflectometers and Stenos Law, to get an accurate identification of a mineral

3.6 Mineral Groups

Distinguish between compositional and structural variations in minerals and provide one example of each.

Mineral Groups

Presentation content:

• Nearly 4,000 minerals have been named
• Rock-forming minerals
  • Only a few dozen
  • Common minerals that make up most of the rocks of Earth’s crust
  • Composed mainly of the eight elements that make up most of the continental crust
• Economic minerals
  • Less abundant
  • Minerals used extensively in the manufacture of products

The eight elements that make up the vast majority of rock-forming minerals

Classifying Minerals

Presentation content:

• Exhibit similar internal structure and chemical compositions are called mineral species.
• Mineral species can be further divided into mineral varieties
  • For example, varieties of quartz
    • Smoky quartz: contains trace amounts of aluminum
    • Amethyst: contains trace amounts of iron
• Mineral species are assigned to mineral classes
  • Silicates, carbonates, halides, and sulfates are different mineral classes.

Silicate Versus Nonsilicate Minerals

Presentation content:

• Silicate minerals are the most common type of minerals
  • Account for >90% of Earth’s crust
  • Silicon and oxygen make up the basic building blocks of silicate minerals
• Nonsilicate minerals are not as common as the silicates but important economically and include the.
  • Carbonates
  • Sulfates
  • Halides

3.7 The Silicates

Sketch the silicon–oxygen tetrahedron and explain how this fundamental building block joins together to form various silicate structures.

Silicate minerals

Presentation content:

• All silicate minerals contain oxygen and silicon

  • The two most abundant elements in Earth’s crust.

• Silicon–oxygen tetrahedron

  • Fundamental building block
  • Four oxygen ions surrounding a much smaller silicon ion
    • Single tetrahedra are linked together to form various structures.

Silicate minerals with independent tetrahedra

Presentation content:

• One of the simplest silicate structures
• Oxygen ions are bonded with positive ions (such as Mg2+, Fe2+, Ca2+)
  • Olivine (Mg, Fe)₂SiO₄
  • Garnet
• Form hard, dense equidimensional crystals that lack cleavage

Polymerization

Presentation content:
SiO₄ tetrahedra can link in a variety of configurations.

• Called Accounts for the high variety of silicate minerals
• Polymerization is achieved by sharing one, two, three or all four oxygen atoms with adjacent tetrahedra.

Joining Silicate Structures

Presentation content:

• Most silicate structures have a net negative charge (except for quartz).
• Positive metal ions are required to balance the charge.
  • These positive ions bond with unshared oxygen ions in the tetrahedra.
  • Most common ions are Fe²⁺, Mg²⁺, K⁺, Na⁺, Al³⁺+,Ca²⁺
• Covalent silicon–oxygen bonds are typically stronger than the ionic bonds of the silicate structure.
• Controls the cleavage and hardness of minerals

3.8 Common Silicate Minerals

Compare and contrast the light (nonferromagnesian) silicates with the dark (ferromagnesian) silicates and list three common minerals in each group.

Light vs. Dark

Presentation content:

• Most silicates form from molten rock cooling and crystallizing
  • The feldspars are the most common silicate group and make up more than 50% of Earth’s crust.
  • Quartz is the second-most abundant mineral in the continental crust and the only common mineral made completely of silicon and oxygen.
• Silicates are subdivided into light (non-ferromagnesian) and dark (ferromagnesian) groups.

Light (Nonferromagnesian) Silicates

• Generally light in color
• Specific gravity of approximately 2.7
• Contain varying amounts of Al, K, Ca, and Na
• Lack Fe and Mg

Dark (Ferromagnesian) Silicates

• Contain iron and/or magnesium in their structure
• Generally dark in color
• Specific gravity between 3.2 and 3.6

Feldspar Group

• Most common mineral group
• Forms under a wide range of temperatures and pressures
• Exhibit two directions of perfect cleavage at 90º
• Two most common members:
  • Orthoclase (potassium feldspar)
  • Plagioclase (sodium and calcium feldspar)

The Light Silicates

Presentation content:

• Quartz
  • Only common silicate composed entirely of oxygen and silicon
  • Hard and resistant to weathering
  • Conchoidal fracture due to three-dimensional framework
  • Often forms hexagonal crystals
  • Colored by impurities (various ions)
• Muscovite
  • Common member of the mica family
  • Excellent cleavage in one direction
  • Thin sheets are clear (Used as “glass” during the Middle Ages)
  • Produces the “glimmering” brilliance often seen in beach sand
• Dark (Ferromagnesian) Silicates
  • Contain iron and/or magnesium in their structure
  • Generally dark in color
  • Specific gravity between 3.2 and 3.6
• Olivine Group
  • High-temperature silicates
  • Black to green in color
  • Glassy luster and conchoidal fracture
  • Forms small, rounded crystals
  • Common in oceanic crust and through to constitute 50% of the Earth’s mantle

The Dark Silicates

Presentation content:

• Pyroxene group

  • Important components of dark-colored igneous rocks
  • Augite is the most common mineral in the pyroxene group
  • Black in color
  • Two distinctive cleavages at nearly 90º
  • Dominant mineral in basalt

• Amphibole group

  • Hornblende is the most common mineral in this group
  • Usually black to dark green
  • Very similar in appearance to augite
  • Two perfect cleavages exhibiting angles of 120º and 60º

• Biotite

  • Iron-rich member of the mica family
  • Excellent cleavage in one direction (sheet structure)

• Garnet

  • Composed of individual tetrahedra linked by metallic ions
  • Glassy luster, lacks cleavage, and has conchoidal fracture
  • Color varies, most often brown-red
  • Well-developed crystals have 12 diamond-shaped faces

3.9 Important Nonsilicate Minerals

List the common nonsilicate minerals and explain why each is important.

Nonsilicate minerals

Presentation content:

• Divided into groups based on the negatively charged anion.
• Makeup approximately 8% of Earth’s crust
  • Carbonates
  • Halides
  • Oxides
  • Sulfides
  • Sulfates
  • Native elements

Carbonates

Presentation content:

• Composed of the carbonate ion (CO₃²⁻) and a positive ion
• Two most common carbonates are calcite (CaCO₃) and dolomite CaMg(CO₃)₂
• Primary constituents in limestone and dolostone
• Used as road aggregate, building stone, and main ingredient in Portland cement.

Economic value of nonsilicates

Presentation content:

• Many nonsilicate minerals have economic value
  • Examples:
    • Halite (mined for salt)
    • Gypsum (building materials)
    • Hematite and magnetite (mined for iron ore)
    • Sulfides (galena: lead; sphalerite: zinc; chalcopyrite: copper)
    • Native elements (gold, silver, and diamonds)

End of Chapter 3 - Concept Checks

3.1 Minerals: Building Blocks of Rocks

1. List five characteristics of a mineral.
2. Based on the definition of a mineral, which of the following—gold, liquid water, synthetic diamonds, ice, and wood—are not classified as minerals?
3. Define the term rock. How do rocks differ from minerals?

3.2 Atoms: Building Blocks of Minerals

1. Make a simple sketch of an atom and label its three main particles. Explain how these particles differ from one another.
2. What is the significance of valence electrons?

3.3 How Atoms Bond to Form Minerals

1. Explain the difference between an atom and an ion.
2. How does an atom become a positive ion? A negative ion?
3. Briefly distinguish between ionic, covalent, and metallic bonding and discuss the role that electrons play in each.
4. Describe three ways minerals can form.

3.4 Properties of Minerals

1. Why is color not always a useful property in mineral identification?
   Give an example of a mineral that supports your answer.
2. What differentiates cleavage from fracture?
3. What is meant by a mineral’s tenacity? List three terms that describe tenacity.
4. Describe a simple chemical test that is useful in identifying the mineral calcite.

3.5 Mineral Structures and Compositions

1. Explain Steno’s law in your own words.
2. Define polymorph and give an example.

3.6 Mineral Groups

1. Distinguish between rock-forming minerals and economic minerals.
2. List the eight most common elements in Earth’s crust.

3.7 The Silicates

1. Sketch the silicon–oxygen tetrahedron and label its parts.
2. What is the ratio of oxygen to silicon found in single tetrahedral? How about in framework structures? Which has the highest silicon content?

3.8 Common Silicate Minerals

1. List eight common nonsilicate minerals and their economic uses.
2. What is the most common carbonate mineral?

3.9 Important Non-Silicate Minerals

1. What does the orientation of transform faults indicate about plate motion?
2. Based on what you see in Figure 2.33, which three plates appear to exhibit the highest rates of motion?