Mineralogy Chapters 1-5
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- What are minerals?
- Naturally occurring, solid, regular atomic arrangement, chemical compound, usually formed by inorganic processes
- Why to we study minerals?
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1.) Help understand rocks, sediments, soils.
2.) Anthropogenic reasons
3.) Some minerals thought to be involved in pre-biotic synthesis - How do we study minerals?
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1.) Visual observation with simple equipment to observe physical properties
2.) Optical microscope
3.) X-Ray defraction
4.) Chemical composition - What does mineral formation depend on?
- The initial composition of the melt and the temperature at which it crystallized.
- What is Bowen's Reaction scale?
- (Highest Temp) Olivine, Pyroxene, Amphibole, Biotite, Ca-Rich Plagioclase Feldspar, Na-Rich Plagioclase Feldspar, Quartz, K-spar, muscovite mica (lowest temp)
- What is the Earth's crust composition?
- Approx. 40 weight % Oxygen, 30% Silicon, Aluminum, Iron, Magnesium, Calcium, Potassium, Sodium, Other.
- What is a simple substitution?
- Two elements of similar size and the same charge.
- What is a coupled substitution?
- Ions of different charge and approx. same size substitute for each other, coupled with two other ions of different charge and approx. same size so that there is no change in charge.
- How do you find the molecular (mol) weight?
- Take the mol weight from the periodic table and multiply by # of atoms and add all together.
- How do you find the atom proportion?
- Take the weight percent and divide by the mol weight.
- How do you find the mol proportion?
- Take the weight percent and divide by the mol weight.
- How do you find the atomic proportion?
- Multiply the mol proportion by the number of atoms. EX. For Al2O3, take the mol prop. * 2 because there are 2 AL's.
- How to you find the formula proportion?
- Multiply the atom proportion by the normalization factor.
- How do you find the normalization factor?
- Divide 5 by the total of the atom proportion column.
- What are the characteristics of metallic bonds?
- good conductors of heat and electricity, typically low hardness because have weak bonds, malleable, ductile, sectile, high specific gravity because of high atomic weight, cubic closest packing
- What are the characteristics of Van der Waals bonds?
- These are residual bonds. Ex. graphite, micas, native sulpher. Weak attraction btwn random dipoles in structure (top part of layer has a different charge than the bottom part of the layer), low hardness, good cleavage
- What are the characteristics of Ionic bonds?
- electrostatic bonds between cations and anions (don't have the same charge but must balance) Ex. halite and fluorite. Medium to high hardness, tend to be brittle, not very good conductors b/c no free electron.
- What are the characteristics of Covalent bonds?
- Ex. diamond, has a tendency to share electrons so makes a very strong bond. Electron clouds overlap, very hard minerals, brittle, insulators.
- What are the characteristics of Quartz?
- Hardness of 7, conchoidal fracture, glassy/vitreous, brittle, striations on planes but not pyramid
- What are the characteristics of Feldspars?
- Hardness of 6, 90 degree cleavage, vitreous/glassy, often dull b/c altered, brittle, Plagioclase feldspar has twins perpendicular to B called polysynthetic twins.
- What are Alkali Feldspar twins called?
- Carlsbad twins. They are interlocking/interpenetrating twins.
- What are the formulas for Alkali Feldspars?
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K Al Si3 O8
Na Al Si3 O8 - What are the formulas for Plagioclase feldspars?
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Na Al Si3 O8
Ca Al2 Si2 O8 - Name some types of Alkali Feldspars.
- Orthoclase, Microcline, Sanidine
- What are exsolution lamellae?
- These occur in slowly cooled plutonic alkali feldspars and are a result of a miscibility gap in which the melt cools to below the misc. gap temp and one type crystallizes out as lamellae and the other type crystallizes as the bulk mineral.
- What are the symmetry aspects of Orthoclase and Sanidine?
- They have a two fold axis perpendicular to a mirror plane.
- What are the symmetry aspects of plagioclase and microcline?
- These do not have a two fold axis or a mirror plane.
- What is a prism?
- Three or more parallel planes or faces
- What are pyramid faces?
- Planes that intersect at a point or could if extended.
- What do parenthesis indicate in Miller indices?
- A crystal face
- What do brackets indicate in Miller indices?
- An axis or a line.
- What is a center of inversion?
- Every point is the same distance away from the center of inversion but on opposite sides.
- What is a polymorph?
- A crystal with the same composition but different crystal structure. Ex. graphite and diamond.
- What are the 6 crystal systems?
- Isometric, Tetragonal, Orthorhombic, Monoclinic, Triclinic, and Hexagonal
- What are the characteristics of Isometric minerals?
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3 equal and perpendicular axes.
A1=A2=A3
A1 perp. A2 Perp. A3 - What are the characteristics of Tetragonal minerals?
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4/m, 2/m, 2/m
Three perpendicular axes, 2 of which are equal
C-Axis can be greater or less than the other two
A1=A2 not= A3 - What are the characteristics of Orthorhombic systems?
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2/m, 2/m, 2/m
A is not perp. to B is not perp. to C
A is not = to B is not equal to C - What are the characteristics of Monoclinic crystal systems?
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Ex. i, A2, m
A is perp to B
B is perp to C
The angle btwn A and C is obtuse
A is not = to B is not = to C - What are the characteristics of triclinic systems?
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A is not = to B is not = to C
No axes at 90 deg. or 60 deg. or 120 deg. to each other
A one fold axis - What are the characteristics of the Hexagonal crystal system?
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C is perp. to the plane of a1, a2, a3
a1 = a2 = a3 and does not = C
The angles btwn a1, a2, a3 is 120 degrees - What does a one fold rotoinversion mean?
- A center of inversion
- What does a two fold rotoinversion mean?
- A mirror plane
- What does a three fold rotoinversion mean?
- A three fold axis and a center of inversion
- What does a six fold rotoinversion mean?
- 3/m or a three fold axis perpendicular to a mirror plane
- What symmetry does the triclinic system have?
- None. 3 axes of different lengths and angles do not = 90 degrees. Possible symmetry is a one fold axis and a center of inversion
- What symmetry does the monoclinic system have?
- Must have a 2 fold axis and/or a mirror plane
- What symmetry does the Orthorhombic system have?
- 3 perpendicular axes of different lengths. Each 2 fold axis is perpendicular to a mirror plane
- What symmetry does the tetragonal system have?
- 3 perpendicular axes, 2 of which are equal. The axis that is not equal is C and C is either a 4 fold or a 4 fold rotoinversion axis.
- What symmetry does the Isometric system have?
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3 equal axes at 90 degrees
4/m, bar 3, 2/m - What symmetry does the Hexagonal system have?
- C axis is perpendicular to the plane of a1, a2, a3, where the angle btwn a's is 120 degrees. C axis is a 3 fold or bar 3 or a 6 fold or bar 6
- How do you find the Miller indices?
- Take the intercepts of A, B, C. Then take the reciprocal of those values. Then clear fractions to find the plane.
- What is a pyramid?
- Three or more faces that intersect at a point
- What is a pinacoid?
- Two parallel faces
- What is a pedion?
- One lonely plane
- What is a dome?
- Two non-parallel faces symmetrical with respect to a mirror
- What is a sphenoid?
- Two non-parallel faces symmetrical with respect to a 2 fold axis
- What is a unit cell?
- The smallest unit that has the same overall symmetry