MINERALOGY BASIC CONCEPTS (CRYSTALLOGRAPHY) Flashcards
Long range order or crystal structure of crystalline substances
Crystallography
What is the basic unit of pattern during crystal growth?
Coordination Polyhedra
Processes which are responsible for the repetition of these basic units into long range structure
Symmetry operation
Techniques whicah can aid in examining internal crystal structures
XRD
AFM (Atomic Force Microscopy)
Smallest unit of pattern repeated to produce a long range pattern characteristic of a crystal
Motif
What s the motif in minerals?
Coordination Polyhedra
A point which represent a motif
Node
Single symmetry Oprations
Translation
Rotation
Reflection
Inversion
Symmetry operation repeating nodes by linear displacement
Translation
Product of 1D translation
Row of similar elements
Product of 2D translation which is an array of motif or nodes in which every node has an environment similar to every other noe in the array
Plane Mesh or Plane lattice
Result 3D Translation
Space Lattice
3d array of motifs (Coordination polyhera) and product of translation in crystalline substances
Crystal lattice
Symmetry operations which repeats a motif by rotation of a pattern about an axis in which every component of the pattern is perfectly repeated one or more times during a complete 360 rotation
Rotation
This denotes the number of repetitions
“n”
A symmetry operation in which a certain pattern is repeated by reflection across a aplane called mirrior plane (m)
Reflection
What changes during reflection
Handedness. (What right in the original image will be on the left of the mirrior image )
Symmetry operation which change the handedness of motifs
Enantiomorphic operations
A symmetry of operations which involves the repetition of a motif by inversion through a center of inversion symmetry (i)
Inversion
What’s the test for inversion?
All patterns are repeated along lines that pass through a common center and are repeated at equal distance from the center
Difference between reflection and inversion
Reflection is repeate across a plane while inversion is repeated across a point of symmetry (i)
Compound symmetry operations which combines Translation and Reflection across a mirror plane
Glide Reflection (g)
An operation that combines rotation and inversion about rotoinversion axis
Rotoinversion (?)
Ten plane point groups
1, 2, 3, 4, 5
1m, 2mm, 3m, 4mm, 5mm, 6mm
Five Unit meshes created by translation
square (p, a=b, ab=90
primitive rectangle p, a/=b, ab=90
Diamond or Centered Rectangle
c, a/=b, ab = cosa/2b
Hexagonal
c, a=b, ab=120
Oblique
p, a/=b, ab/=90
How are unit mesh classisifed
Length of Vetors
Angle between 2 translation verctors
Positions of Nodes (P or C)
If the nodes of a unit mesh are all on the corners it is
Primitive
If the a node exist at the center of a unit mesh
centered
When five unit meshs is combines with 10 point groups this much plane lattice group forms
17 lattice groups
3D equivalent of 10 plane point groups which are the products of non translational symmetry operations
Space Point groups
3D equivalent of plane nets
Splace Lattices
Fundamental units of space lattices
Unit cells
Consist of 3D set of one or more crystal faces that possess similar relationships to the crystallographic axees
Crystal Forms
have the potential to completely enclose a mineral specimen and therefore to exist alone in perfectly formed euhedral crystals
Closed Crystal Forms
Crystal systems of closed crystal forms
Isometric
Tetragonal
Hexagonal
orthorhombic rhombohedral
a typical closed crystal form of pyrite
Pyritohedron
Do not have the potential to completely enclose a mineral specimen and so must occur in combination with other open or closed crystal forms
Open Crystal Forms
Consist of only a singe face
Pedians monohedron
Consist of pair of parallel face
Penacoids parallelohedron
three of more faces that paralle to an axis
Prisms
Three or more faces that intesect to an axis
Pyramid
A pair of faces symmetrical about a mirror plane (changes handedness)
Domes
A pair of faces symmetrical about an axis of rotation (donot change handedness)
Sphenoid
How to calculate axial ratios?
a/b: b/b: c/b whre b/b is always 1
Unit of axial lengths
Angstroms (A)
Planar features that are characteristic of a mineral
1) Crystal lattice planes that reflects xray
2) Cleavage surfaces that develop during breakage
3) Crystal face that foms during growth
Euclidean Principle
Planes must at least intersect one axis and be parallel to the other 2
What does miller indices do?
Identify and describe crystallographic planes
Any face or plane that intersects all three axes at distances from the center corresponding to the axial ratio of the mineral
Unit Face or Unit Plane
Any face of plane that intersect all three crystallographic axes at different lengths relative to their axial ratio
General Face
How to get Weiss parameter?
Just divide the actual length of the face or place intercept to the axial lengths or ratio
A method for describing the relationships between sets of crystal faces or planes and the crystallographic axes using rational numbers (Fraction)
Weiss Parameters
Weiss parameter of unit planes or faces
1:1:1
IN weiss parameter, how are planes that intercept to the negative crytallographic axes denoted?
By placing a bar over their weiss parameter
Weiss parameter of a face that intersects c and is parallel to a and b axes
(Infinity, Inifinity, 1)
If a face is parallel to a crystallographic axes the weiss parameter on that specific axes for such face is
Infinity
if the weiss parameter is 1 at a specific axis it denotes that
the plane intersect such axis at unit length
Whats the relationship of the Miller Indices to Weiss Parameter?
Reciprocal (Miller tend to be a whole number)
Thus what is the miller index of a plane parallel to an axes?
0
the larger the Miller index
the smaller is the actual length of interception
A miller indices of (123) are read
planes intersect a-axis at unity
plane intersect b-axis at 1/2 unity
plane intersect c axis at 1/3 unity
How is an intersection between the negative crystallographic axes and the plane denoted in miller index?
a bar above the index
If the faces or planes has the same general relationship to the crystallographic axes and therefore have the same miller index, what can be the shortcut?
Form Indices
Whats the preference for the Form Face whenever the indices has a common form
1) Top Face
2) Top right
3) Top right front
Form indices of octahedral minerals
{111}
Form indices for cube
{001}
Form indices for dodecahedron
{011}
Chalcopyrite is has what crystal form?
Tetragonal Disphenoid
Vesuvianite and wulfenite has one crystal form?
Basal Pinacoid, tetragonal-pyramidal
Why is there twinning?
Because there are shared lattice points between two crystals
The mirror plane that caused reflection of twins
Twin Plane
Axis of rotation in twin crystals
Twin Axis
Twins that formed by inversion through a point have
Twin Center
The symmetry operation that relates twin in twinned crystals
Twin Law
Surfaces along which twins are joined
Composition Surfaces/Planes
Twins joined along composition planes
Contact twins
A contact twin in orthoclase with {021} as twin plane
Braveno Law
Twins joined along irregular composition surfaces defined either by twin center or twin axis
Penetration twins
Twin axis of Carlsbad Law a type of penetration twin
[001]
Irregular composition surfaces that are repeated but are not Parallel
Cyclical Twins
Mineral with cyclical Twins
Chyrosberyl
Crystals that contain only two twins
Simple twins
More than two twins
Multiple Twins
Multiple twins repeated across multiple parallel composition
Polysynthetic Twins
Polysynthetic twinning with {010} Twin Plane
Albite Twin Law
Twins that form durig crystal growth
Growth Twins
Twining occurs when a preexisting crystal undergoes a transformation due to acchange in pressure or temperature producing symmetry
Transforamtion twins
Example of Transformation twins
Tartan Twinning in Microcline
Brazil and Dauphine Twinning in Qtz
A mechanical twinning that forms during deformation when atoms are pushed out of place and produce a symmetrical arrangement
Deformation Twins/Mechanical Twins
Mineral that exhibit Deformation Twins
Calcite (102)
Twinning in Gypsum
Swallow tail
Twinning in Plagioclase
Polysynthetic Albite
Twinning in Galena, Pyrite and Staurolite
Penetration twins
Twinning in Orthoclase
Carlsbad
Small scale impurities or imperfection or local scale inhomogenities that cause mienral composition and/or structure to vary from the ideal
Crystal Defects
Formed when ions in question move to an interstitial site leaving unoccopied structural sites or vacanies behind. Does not cause charge imbalance but only lattice distortions
Frenkel Defect (VACANCY)
A point defect wherein ions migrate oustide the lattice or were never there at all thus creating charge imbalance which can be balanced by creating a second vacancy or inducing ions that will balance the charge
Schottky Defect (CHARGE IMBALANCE)
Example of Mineral that normally exhibits Schottky Defect
Pyrrhotite
Defects on atomic scale and thus don’t have longer range extent and is considered to be ZERO DIMENSIONal
Point Defects
Point Defects
1) Substitution
2) Interstitial
3) Omission (Vacancy)
Line defects which commonly result from SHEARING STRESSES produced in crystals during deformation causing atomic planes to shift position thus producing distortion in the lattice
Permits rocks to deform withut fracturing
Dislocations
Dislocation in which the slip plane is normal to the dislocation
Addition of half a plane
Edge
Dislocation in which the slip plane is parallel to the dislocation (Rotated)
Screw
2D Crystals defects and where crystal srtucture changes across a distinct planar boundary
Planar Defects
Diffusion wherein vacancies and ions move towards the region of low stress which tends to lengthen the crystal in that direction which is the grain boundaries
Coble Creep
Diffusion wherein vacaneis and ions move towards the region of highest stress which tend to shorten the crystal
Herring-Nabarro Creep
Low Temp, Low Strain
Dissolution Creep (Pressure solution) and Mechanical Twinning
Low Temp, High Strain
Cataclasis
Mod Temp, Low Strain
Cobble Creep
High Temp Low strain
Herring-Nabarro Creep
High Temp, High Strain
Dislocation Creep
Grains tend to migrate to the region of
Minimum Stress
Vacancies tend to migrate to the region of
Max Stress
