Mineralogy GEOL-3121

Fall 2009

Review for 1^st Lecture Test

Introduction (Chapter 1)

1) What is the definition of mineralogy? List the subfields that are included in this study.

2) What is the definition of mineral? Explain why the definition no longer includes the term ‘inorganic’? List the 8 most abundant elements found in the earth’s crust. Which mineral group is the most abundant?

3) What are mineraloids? Give examples and explain how they differ from minerals.

4) What criteria must be met for a new mineral to be named? What is the basis for most mineral names?

Crystallography (Chapter 2)

1) What is the definition of crystallography? Describe how early crystallography studies led to the theory of the atom and atomic structure.

2) Describe the two major ways in which crystal structures are described (translation and point symmetry). What is the unit cell? What types of structures are described using translation?

3) Name the six crystal systems and describe the axial lengths and angles that define each of these. How do these relate to Bravais Lattices? Name examples of at least 2 minerals for each crystal system. What is the easiest way to determine the crystal system of a mineral?

4) Name and describe the three symmetry operations used to define point groups. What are the 32 crystal classes and how are they defined? What are Herman-Mauguin Symbols? Describe how you can determine the crystal class of a mineral sample.

5) How are the most detailed crystal structures defined (the 230 space groups)?

6) What is Steno’s Law and how does it relate to describing crystal form? How are crystal faces measured and described?

7) What is the relationship between crystal form and the unit cell? What units of measurement are used to define the unit cell of a mineral? How is this unit cell described? What are formula units (Z)?

8) What are Miller Indices and how are they used? Be able to describe the orientation of crystal faces or cleavage directions using these indices such as (1 1 1), (0 0 1) and (112).

9) How are stereographic projections used to describe crystal form and internal features? Which type of stereographic projection is most commonly used in mineral studies, equal area or equal angle? Explain why one is more appropriate.

10) Describe the relationship between crystal faces and the unit cell. Why do minerals only display a limited range of crystal forms? Define the following terms: euhedral, subhedral and anhedral.

11) Compare and contrast crystal form and habit. Give several examples of crystal habits.

Optical Mineralogy (Chapter 7)

1) Compare and contrast the particle-like and wave-like theories of light. List some of the supporting evidence for both theories. Which theory best explains how light interacts with minerals?

2) What is electromagnetic radiation? What is the relationship between wave length and energy? Define the following wave components: wavelength, amplitude, wave front, wave normal, and light ray.

3) Compare and contrast frequency and velocity. Describe the factors that control these measurements. How can frequency changes in electromagnetic radiation be easily recognized? Describe how frequency remains constant even when light velocity changes as it goes through minerals and materials.

4) Describe wave interference and retardation. How does this retardation result in result in some wavelengths (colors) being transmitted and others being blocked?

5) What is refraction and why does it occur? What is Snell’s Law and how does it describe refraction? Be able to write Snell’s Law. What are the major factors that control the index of refraction in minerals? What is dispersion and why does it occur?

6) What is the Critical Angle? How does it control the appearance of a mineral? Name an example of a mineral with a high critical angle that display a brilliant luster because of this property.

7) Define polarization and describe three ways in which polarized light can be produced. Describe how polarized light used in petrographic microscopes to study minerals.

8) What is the Index of Refraction? Why is relief considered a qualitative measure of the index of refraction? How are quantitative measurements of the refractive index of a mineral determined? Describe how the Becke Line Technique is used to obtain precise measurements of the refractive index of a mineral.

9) Name and describe isotropic materials. Why do isometric minerals display isotropic behavior? How are isotropic materials easily recognized using the petrographic microscope? Which other properties are used to distinguish different isotropic minerals and materials?

10) Which crystal systems are anisotropic? Why do anisotropic minerals display double refraction? Compare and contrast the slow and fast rays with the ordinary and extraordinary rays in anisotropic materials. What is the relationship between the ordinary ray and symmetry within anisotropic minerals?

11) What is an optic axis? Compare and contrast uniaxial and biaxial minerals by describing differences in crystal structure and symmetry. List the crystal systems that belong in each group.

12) Define and describe birefringence and the resulting interference colors. What are the factors that control birefringence? How is birefringence measured in minerals? What is difference between pleochroism and birefringence?

13) What is extinction and when and why does it occur in anisotropic minerals when viewed under cross-polarized light? Name and describe the three types of extinction. What are extinction angles and how are they measured?

14) What are interference figures and how do they form? Which components of the petrographic microscope are used to obtain these figures? Define the following components of interference figures: isochromes, melatope, and isogyres.

15) What is the indicatrix and how is it used? How does a uniaxial indicatrix differ from a biaxial indicatrix? Compare and contrast biaxial negative and positive indicatrices.

16) Describe how the orientation of a mineral controls its birefringence. Be able to describe which crystallographic positions produce the highest and lowest birefringence.

17) Compare and contrast the following uniaxial interference figures: centered optic axis, off-center optic axis, and optic normal. Be able to describe the components and crystal orientation that produces each of these figures.

18) Compare and contrast the following biaxial interference figures: acute bisectrix, centered optic axis, obtuse bisectrix and optic normal. Be able to describe the components and crystal orientation that produces each of these figures.

19) Describe how the optic sign, birefringence and indices of refraction are measure for uniaxial minerals. Describe how the 2V, optic sign, birefringence and indices of refraction are measured for biaxial minerals.