Materials of Solid Earth
Define Mineral
A mineral is naturally occurring, solid, usually inorganic, has a crystalline structure and has a specific chemical composition.
Define Electronegativity and Ionization energy
Define crystallography and describe its key aspects.
Crystallography is the scientific study of crystals and their structures. It involves examining how atoms, ions, or molecules are arranged in a crystalline solid.
Key aspects include:
What happens when thin sections interact with light?
When a thin section (a very thin slice of rock) interacts with light, particularly when viewed under a polarizing microscope, the different minerals within the rock exhibit unique optical properties, causing them to display varying colors and interference patterns depending on their crystal structure and orientation, allowing geologists to identify minerals based on how they interact with polarized light; this phenomenon is primarily due to a property called "birefringence" where light travels at different speeds within the mineral depending on its direction.
Magmatic and metamorphic rocks: how do you recognize them?
Magmatic Rocks – Mineral size, texture
- Intrusive (Plutonic) – rocks cool slowly
- Extrusive (Volcanic) – rocks cool fast
Metamorphic Rocks – Foliation, texture
Describe the different types of atomic bonds.
What are the 5 types of 2-D lattices?
1. Square: All sides equal, angles 90°.
2. Rectangular: Unequal sides, angles 90°.
3. Hexagonal: Equal sides, angles 120°.
4. Rhomboidal (Parallelogram): Equal sides, no 90° angles.
5. Oblique: Unequal sides, no 90° angles.
How are crystal systems and optical properties related?
Crystal systems and optical properties are directly related because the arrangement of atoms within a crystal lattice (its crystal system) determines how light interacts with the material, leading to specific optical behaviors like birefringence, pleochroism, and different refractive indices depending on the direction of light propagation through the crystal; essentially, the symmetry of a crystal system dictates its optical behavior.
Silicates: What are they and why are they common?
Silicates include Si and O. Which are some of the most abundant elements on Earth. Silicates make up 92% of the Earths crust.
How do bonds affect the physical properties of minerals?
Atomic bonds significantly influence a mineral's physical properties like hardness, cleavage, density, and melting point, as the strength of the bonds between atoms determines how easily a mineral can be broken, deformed, or melted, with stronger bonds generally leading to harder, more resistant minerals; the type of bond also affects properties like conductivity and crystal structure.
What are Miller Indices?
Miller indices are a set of three integers (h, k, l) that describe the orientation of a crystal plane within a crystal lattice.
Define the optical mineral properties
1. Refractive Index (RI) - Measures how much light slows down when passing through a mineral. Higher RI = more bending of light.
2. Birefringence - Difference in refractive indices along different crystallographic directions. Results in interface colors under cross-polarized light.
3. Pleochroism - Change in color when the mineral is viewed from different angles under plane-polarized light. Common in anisotropic minerals like biotite and hornblende.
4. Extinction - The mineral goes dark at specific angles as the stage is rotated under cross-polarized light.
5. Interference Colors - Colors produced by the interference of two rays in birefringent minerals. Determined by the mineral's birefringence and thickness.
6. Relief - The degree to which a mineral stands out from its surroundings under the microscope.
7. Cleavage - The tendency to break along specific planes. Visible is straight lines or stepped features in thin sections.
8. Twinning - Intergrowth of two or more crystals with specific symmetrical relationships. Appears as repeating patterns or lamellae under polarized light.
Which elements are common in the crust and the whole Earth?
Describe coordination number and its relevance to ionic radius and charge
Coordination number refers to the number of ions of opposite charge that directly surround a central ion in a crystal lattice, and it is significantly impacted by the ionic radius and charge of the central ion, with larger ions generally having a higher coordination number due to their ability to accommodate more surrounding ions of opposite charge; essentially, the size of an ion determines how many other ions can fit around it in a stable arrangement.
What are the 6 crystal systems and describe their properties.
1. Cubic: All axes are equal in length and all angles are 90 degrees, exhibiting high symmetry.
2. Tetragonal: Two axes are equal in length and perpendicular to a third axis of different length, all angles are 90 degrees.
4. Orthorhombic: All axes are unequal in length and all angles are 90 degrees.
5. Monoclinic: Three unequal axes, with one angle not equal to 90 degrees.
6. Triclinic: All axes are unequal in length and all angles are different from 90 degrees.
What are the basic physics of light and how microscopes work.
A microscope works by using lenses to bend light rays passing through a specimen, creating a magnified image by focusing the light onto the viewer's eye; the basic physics involved are the refraction of light through curved surfaces, where different densities of material cause light to bend, allowing for the magnification of small objects by focusing the light rays into a concentrated image on the eyepiece.
Name the common mineral groups
1. Silicates – contain O and Si
2. Carbonates – contain C and O
3. Oxides – contain O and metallic cations
4. Sulfides – contain S and metallic cations
5. Sulfates – contain SO4 and metallic cations
6. Halides – contain Cl, F, I, or Br
7. Hydroxides – contain OH
8. Native elements – masses of all the same element metallically bonded
9. Tungstates – contain W and O
10. Phosphates – contain P and O
Pauling’s Rules (be able to explain each in detail and problems with them)
1. The Coordination Principle: Basically, this rule says the larger the ionic radii the greater the cation-anion distance (or the lower the radius ratio the lower the coordination number). This is a great predictive tool for understanding the atomic coordination of atoms in minerals.
2. The Electrostatic Valency Principle: The strength of an ionic bond is equal to the ionic charge divided by the coordination number.
3. Sharing of Polyhedral Elements I: Sharing faces or edges between coordinating polyhedral is inherently unstable.
4. Sharing of Polyhedral Elements II: Cations of high valance (charge) and small coordination number tend not to share polyhedral elements with each other.
5. The Principle of Parsimony: The number of essentially different kinds of constituents in a crystal tends to be small. It means nature is simple. Minerals are made up of the fewest number of sites possible. Many different elements can substitute into these sites and the structure is preserved.
Rotations, Mirrors, Rotoinversions: what are they and can you identify symmetry elements on a given 3-D shape or 2-D drawing?
Rotation: Rotating an object around an axis by a certain angle so that it appears unchanged.
Mirror Plane (Reflection): Reflecting an object across a plane to produce a mirror image.
Rotoinversion: A combination of rotation and inversion through a center point.
Describe the difference between uniaxial and biaxial.
In mineralogy, "uniaxial" refers to a crystal with only one optic axis, meaning light travels through the crystal with the same properties in one specific direction, while "biaxial" describes a crystal with two optic axes, where light behaves differently depending on the direction it travels through the crystal; essentially, uniaxial minerals have a single axis of optical symmetry, whereas biaxial minerals have two distinct axes of optical symmetry.