MINERALOGY BASIC CONCEPTS (CRYSTALLOGRAPHY) Flashcards by Sean Levi Abiera

Long range order or crystal structure of crystalline substances

Crystallography

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What is the basic unit of pattern during crystal growth?

Coordination Polyhedra

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Processes which are responsible for the repetition of these basic units into long range structure

Symmetry operation

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Techniques whicah can aid in examining internal crystal structures

XRD
AFM (Atomic Force Microscopy)

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Smallest unit of pattern repeated to produce a long range pattern characteristic of a crystal

Motif

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What s the motif in minerals?

Coordination Polyhedra

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A point which represent a motif

Node

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Single symmetry Oprations

Translation
Rotation
Reflection
Inversion

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Symmetry operation repeating nodes by linear displacement

Translation

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Product of 1D translation

Row of similar elements

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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

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Result 3D Translation

Space Lattice

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3d array of motifs (Coordination polyhera) and product of translation in crystalline substances

Crystal lattice

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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

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This denotes the number of repetitions

“n”

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A symmetry operation in which a certain pattern is repeated by reflection across a aplane called mirrior plane (m)

Reflection

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What changes during reflection

Handedness. (What right in the original image will be on the left of the mirrior image )

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Symmetry operation which change the handedness of motifs

Enantiomorphic operations

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A symmetry of operations which involves the repetition of a motif by inversion through a center of inversion symmetry (i)

Inversion

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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

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Difference between reflection and inversion

Reflection is repeate across a plane while inversion is repeated across a point of symmetry (i)

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Compound symmetry operations which combines Translation and Reflection across a mirror plane

Glide Reflection (g)

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An operation that combines rotation and inversion about rotoinversion axis

Rotoinversion (?)

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Ten plane point groups

1, 2, 3, 4, 5
1m, 2mm, 3m, 4mm, 5mm, 6mm

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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?

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

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