Geos 250 Mineralogy – Final Exam Study Guide
Winter 2012
I. Concepts to review for vocabulary, definitions and correct useage as well as for
essay topics.
A. Chapters in Klein & Dutrow covered: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14 & 19,
especially Ch 5 onwards.
B. Topics:
1. Rock forming minerals: names, some formulae, some substitutions,
structural groups and occurrence.
2. Weight percent oxide or element analyses versus stoichiometry. Be able to
recognize and distinguish major rock forming mineral types, given their
chemical formulae or compositions. For instance, given orthopyroxene you
should think/recall (Mg,Fe)SiO3 or given Al2SiO5 you should think
aluminosilicates Relationship between stoichiometry and chemical formulae
for ionic charges, sizes and substitution.
3. From Ch-5, what are the 3 kinds of substitutions for solid solutions in
minerals and provide an example of each type of substitution and a mineral
(pair or group) it occurs in? What 4 factors govern or control the degree of
solid solution in minerals and explain how this works (I.R., charge, P/T
conditions and availability or bulk composition of the surroundings). What
are omission and interstitial solid solution?
4. Crystallography, internal order and symmetry (graphical symbols of
symmetry elements, stereo-projections and Hermann-Mauguin notation), 32
bravais lattices and point groups, 6 (7) crystal systems. Miller indices and
common crystal forms versus symmetry by system: hkl triclinic etc. Special
closed crystal form names versus crystal system: isometric-cube,
dodecahedron, gyroid; Hexagonal (Trigonal)-rhombohedron etc.
5. Among the possible symmetry elements in the Hexagonal system is the
Crystal Class 32 while in the Cubic system is 23. Why are these unique and
different from one another? What are the other possible symmetries in the
Hexagonal and Cublic systems? Why is 6mm different than 622 and name or
draw and label a possible crystal form for each of these? Do this also for 23
and 2/m 3 in the Cubic system. What system do 422 and 4mm belong to?
What system has 3 unequal unit cell edges but all are 90° apart? What
crystal system has 3 unequal cell edges and only 1 non-right angle? See Ch-6
p126-129 for thumbnails, shorthand notation and help on these concepts.
6. How is the stoichiometry related to the unit cell in minerals? Is one unit cell
comprised of 1 formula unit, why or why not?
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7. Crystal growth and what controls (form, zoning, twinning, colour,
magnetism). What are some common twin types in rock forming minerals
and their useage or application.
8. Polymorphs and phase transitions. What are they and give 2-3 examples and
explain how do they form or change as a function of envrionment. What are
2 different types of phase transitions for a single component system (e.g. SiO 2
or CaCO3 ) what phases (minerals) are they between and when/how do they
occur?
9. Relational concepts and terminology covering (structural groups, solid
solution, coordination polyhedra, ionic charge, lattice energy, defects, causes
of colour and particular physical properties). If you come up with a concrete
mineral example for each term, it will help ground you and stop you from
being too vague on an essay question.
10. Basic optical properties. Photons and electrons, reflection versus
transmission, speed of light, refraction, refractive index, Snell’s Law, critical
angle, relief, polarized light, opaque, isotropic, uniaxial and biaxial minerals.
Epsilon, omega, alpha, beta gamma, delta, birefringence, 2V and how they
vary by crystal class or symmetry.
11. Analytical methods for mineral structure, symmetry and composition. The
generation of X-rays in minerals and metals. Characteristic emission
lines/wavelengths. Bragg’s Law and d spacing of lattice planes. Theta, 2theta,
d values, nλ =2dsinӨ . How do high energy electrons and x-ray photons help
to characterize the composition of minerals in the electron beam instruments.
What are SEM, STEM, TEM and EMPA techniques their capabilities and
instrumentation? Be able to describe what these can do and what they tell us
about minerals.
12. Know how common rock forming silicates relate to the basic structural types
and degree of polymerization based on the silica tetrahedral. E.g. quartz,
feldspar are tectosilicates, beryl and cordierite are cyclosilicates for all 6
silicate types: neso- through phyllo-. This relates to the chemical formulae
given either the relation of Si to O or Si to other metals. E.g. Nesosilicates
have SiO4 or SiO5 groups and abundant other cations to balance the charges
or other polyhedral to complete the framework. Are there other elements
that coordinate with oxygen to make polymers and polyhedral to form
minerals? If so what are some examples of each (element, polyhedral
structures).
13. How does the radius ratio of the cation to anion influence the packing
geometry in minerals? Are all +4 cations (Si, Mn, Ti, Mo etc.) in tetrahedral
coordination, why or why not?
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C. Short Calculations
1. Conversion of mass to moles or vice versa, give weight percent mineral
analyses or stoichiometries and atomic weights. If I gave you an Iron Oxide
analysis could you tell me if it was hematite or magnetite?
2. Calculation of optic sign and birefringence or delta given principle refractive
indices nε and nω or nα and nγ ?
3. How is the refractive index n related to the speed of light c and why do these
quantities both tend to vary between minerals or with composition in a single
mineral? What is it about the minerals that makes these quantities vary?
Can we use this in any informative way?
4. Refractive index and critical angle calculation from Snell’s Law: sin(i) ni =
sin(r) nr .
5. Be able to recognize from a list of minerals which ones would likely be:
isotropic, uniaxial, birefringent (low, high) and pleochroic. What is it that
enables some minerals to be dichroic or pleochroic in plane polarized light?
How does pleochroism (play of colours) relate to lattice orientation and the
presence of transition metals either inherently or as small impurities. Why
are biotite, hornblende and staurolite all pleochroic and what colours do they
tend to show in PPL in thin section?
6. Bragg’s Law and d spacing from X ray wavelength and 2theta or theta for a
diffraction peak position. How could you tell a simpler cubic or hexagonal
mineral from a monoclinic or triclinic one just by a quick glance at their xray diffraction scans? (hint: what does a cubic lattice have lots of that
triclinic ones lack?)
C. Essays: synthesis questions involving concepts or drawings from part A.
1. Draw the indicatrix and relate the refractive indices to the crystallographic
symmetry for a given isotropic, hexagonal; tetragonal, orthorhombic,
monoclinic or triclinic mineral.
2. Be able to match common minerals by name or formula to their typical
crystal form or at least be able to tell them. E.g. If I give you an octahedron,
a rhombohedron, a right prism and a combined hexagonal prism+pyramid
and 4 mineral names like fluorite, dolomite, enstatite and quartz could you
do the where’s Waldo thing and match them correctly and show me their
principal symmetry elements on my drawing?
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3. Given a graphic display of how some physical or optical properties vary
across a solid solution series for 2 end member compositions, be able to
discuss how composition or the structural changes are responsible for the
property variation.
4. Be able to write me a “stellar quality” essay comparing and contrasting 2
common minerals from a list of paired minerals including their structural
and symmetry differences, likely geological environments of formation,
economic value and weird but wonderful curiosities that characterize and
distinguish them. E.g. Wollastonite versus Augite, Graphite versus
Molybdenite.
5. What are the most common mineral structures for the whole of the Earth
and how do these few mineral forms dominate the internal layers inside the
planet?
D. Be able to read and interpret an example mineral table of composition,
stoichiometry, crystallography or descriptive data with focused questions to see how
well you understand and can use data from mineral descriptions.
E. Given a drawing of a crystal form could you find and label the common
symmetry elements and suggest which minerals from a given list of names or
formulae might form this way?
F. Given the name of a particular group of minerals (sulfides, carbonates,
phosphates, silicates, oxides, hydroxides, sulfates, borates, native elements etc.) be
able to recognize a listing of mineral manes that pertain to this group and match
them with the group name. For example: match Hydroxides with: (brucite, gibbsite,
limonite) or Carbonates with: (anglesite, aragonite, azurite, magnesite,
rhodochrosite).
G. What makes a mineral a precious or a semi-precious gem and provide examples
of each type including how they are formed and what types of geological
environments they are found in?
H. We mine the earth and reduce or break down mineral compounds to obtain the
metals and many of the non-metals we use. Why don’t we obtain Oxygen or
Hydrogen from minerals and rocks here on Earth? Go through the periodic table
and pick the mineral that is the most common or has the highest concentration of
that element. Be able to match a list of mineral names to the element they are mined
for. For example: Spodumene – Li, Beryl – Be, Trona – Boron, Fluorite – F, Halite –
Na and Cl, Magnesite – Mg, Boehmite or Gibbsite – Al, Quartz – Si, Apatite – P,
Pyrite or native S – S, Sylvite – K, Calcite – Ca. What about the transition metals?
Be sure you can do this for: Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ag, Pt, Au,
Ag, Pb, Ce, Th & U. Why don’t we use gypsum or anorthite for Ca, or Biotite for
Fe? What determines whether a mineral is useful as an ore for a particular element?
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I. What environmental issues are related to particular minerals in ore deposits or
mineral mining? Be able to provide 2-3 examples including the mineral name, its
composition and the issue associated with its mining, milling or ultimate useage.
J. Example multiple questions for true-false, multiple choice, mix and match or fill
in the blank:
1. Crystal forms which include pyramids or di-pyramids all have 3 or more
faces which are __________.
A. triangles
B. squares
C. rhombs
D. rectangles
E. trapezoids
2. ________ is a common, rock-forming, sulphide mineral that crystallizes with
striated square or pentagonal faces.
A. Pyrite
B. Halite
C. Garnet
D. Epidote
E. Torumaline
3. Common twin laws in both Plagioclase and Alkali feldspars include the
___________ twin laws.
A. Albite, Carlsbad, Pericline
B. Japan Dauphine and Brazil
C. Rhomb diagonal and Swallowtail
D. Cruciform and Cyclic
4. Magnetic moment in minerals results from ___________.
A. un-paired and aligned electron spins in d- or f-block elements
B. the Earth’s magnetic field orienting silica tetrahedral
C. special mystical properties
D. diamagnetism from paired electrons in ions with complete outer shells
E. crystallized solid oxygen
5. Which of the following minerals represent important structures for the most
abundant rock formers in the interior of the solid earth?
A. Feldspar, Olivine, Spinel, Perovskite and Wustite
B. Beryl, Cordierite and Papagoite
C. Gypsum, Kaolinite and Zeolites
D. Gold, Frankincence and Myhrr
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