MIDTERM Flashcards
Xeral Definition
Naturally ocurring crystalline solid.
no human made, found a sample in natural enviro, usually inorganic
Liquid mercury NOT. Glass (amorphous) NOT Xtalline: atoms/ions are arraned and chemically bonded w/ a regular and repating long range order.
Physical Properties
- Appearance (form and habit)
- Interaction w light (luster, color, streak mineral powder, luminescence)
- Mechanical properties (hardness, cleavagem fracture and parting)
- Mass (density & spec. grav)
- Miscellaneous (magnetism, taste, odor, acid reaction)
Fundamentally controlled by structure and chemical composition
Appearance
Form:
* Prismatic
* Rhombohedral
* Cubic
* Octahedral
* Dodecahedral
Quality of form:
* euhadral, subhedral, anhedral
pg 23
Crystal Habit
- Granular
- Equant
- Blocky
- Lamellar/Foliated/Mica
- Bladed
- Fibrous
- Acicular
- Radiating
- Globular
- Dendritic
- Botryoidal
- Oolitic
- Banded
- Concentric
- Drusy
- Geode
pg. 25
HOW IT FORMS, either individual xtals or aggregates
Physical Prop.
Luster
- Metallic/Submetallic
- Vitreous: glassy, not always transparent (high diaphaneity)
- Resinous
- Greasy: biotite
- Silky: composed of fine fibers (selenite variety of CaSO4)
- Adamantine: bright, brilliant (diamond)
- Pearly: iridescent, TALC.
- Dull: does not reflect
Luminescence
Temporary absorption of specific light wavelengths and releasement as a different wavelength
Hardness
- Talc
- Gypsum
-FINGERNAIL- - Calcite
-COIN- - Fluorite
- Apatite
-KNIFE/GLASS- - Feldspar
-STEEL- - Quartz
- Topaz
- Corundum
- Diamond
Cleavage Definition
Tendency for xeral to break as smooth planar surfaces. Way it breaks does not follow face angle (facies is the way it grew overtime chemically). Halite has 3 degrees at 90 (x,y,z) so it forms a cube
Cleavages
- Biotite/muscovites
- Orthoclase/Plags 2 good directions at 90. Hornblende/Amphibole has it at 124
- CUBIC if at 90 (halite, galena). Calcite at 105 and 75
- Octahedral cleavage (fluorite)
Fracture Types
- Even: breaks in smooth planar surface (halite)
- Uneven/Irregular: breaking to produce rough and irregular surfaces
- Hackly: jagged, surfaces, sharp edges
- Splintery: sharp splinters
- Fibrous: forms fibrous material
- Conchoidal: curved surfaces (quartz)
Symmetry
- Unit cell is minimum # of ions you can use to infinit. repeat form. The smallest divisible unit of a xeral w symmetry and properties of the xeral
- Cubic unit cell does not mean cubic external form
- Cube, dodecahedron, octahedron, tetrahedron all subic unit cells
Point groups defined by the external symm of a xeral - Rotation Axes
- Mirror Planes
- Inversion about central point
- Roto+Inversion
Translational Symm
Pattern can be moved and still look the same. Movement of a motif in 1-3 dimensions
* Directional: pattern must be moved in specific direction and distance
* RepetitiveL pattern repeats itself at regular intervals
* No Fixed Point
In a 2D lattice, u can produce a plane lattice with nodes connected by xtal lines. Creates the unit cell. Square, rectangle, diamond, hexagon, or oblique
pg. 67
Point Symmetry
How pattern can be repeated about a point.
* Central point: moved around central point
* Rotational movement: pattern is ROTATED NOT TRANSLATED
* Angles: shape looks the same after rotation by specific angles
* Mirror symmetry on your face
3D Translation Symmetry
Stacking plane lattices (square, rectangle, diamond, hexa, oblique) in 3D creates a space lattice. Voume outlined by lattice nodes is unit cell with edges parallel to xtal axes (a, b, c).
Bravais Lattices are the 14 space lattices that can be produced
Bravais Lattices
6 groups
1. triclinic
2. monoclinic
3. orthorhombic
4. hexagonal
5. tetragonal
6. isometric
Xtal Systems (Bravais)
- Triclinic: a≠b≠c. NO 90. No symm, may have i
- Monoclinic: a≠b≠c. a90, b>90, y90. 1A2 or 2bar
- Hexagonal: a1,2,3 ≠ c. a90, b120, y60. 1A6 or 6bar. Trigonal: 1A3 or 3bar
- Orthorhombic: a≠b≠c. ALL90. 3A2, rarely A2 2bar.
- Tetragonal: a=b≠c (stretched cube). ALL90. 1A4 or 4bar
- Isometric: a=b=c. ALL90. 4A3 or 3bar
Rotational Axes
An or n= # of rotations that can be repeated by a certain angle
* A2: from 0-360 you get the same motif 2x
* A3: motif repeats 3x (triangle)
* A4
* A6
Mirror Planes
Cube: 9m
Butterfly: 1m
Circle: infinit
Inversion Center
Any line drawn through center will fall onto an qual and opposite face, edge, or corner (i)
Rotoinversion
1bar: rotate 360 and invert
2bar: rotate 180 and invert
3bar: 120 and invert
4bar: 90 and invert
6bar
RotoInv & Symm Relationships
2bar: mirror plane perpendic. to A2
3bar: A3 + i
4bar: unique
6bar: A3 w mirror plane perpendic. to rotation axis
Hermann Symbols
4, 4/m, 4bar, 2, 2/m
Cubic system with A4 perpendicular to mirror plane, rotoinversion axis of 4 (90 rot), A2 perpendicular to mirror plane
Law of Bavrais
Faces most likely to form on a xtal are parallel to lattice planes that have a high density of lattice points
Steno’s Law
Angles between equivalent faces of xtals of the same susbtance, measured at the same temperature, are constant
Weiss Intercepts
Indexing faces: mark if/where the projection of a face will intersect axis.
* infinites are 0
* 2 congruent but diff sized faces intersect axis at different points (problem) –> fixed with MILLER
WEISS-MILLER
1. change to reciprocal (1/x)
2. Find common denominator and multiply through
3. Reduce fraction
4. Bar over negative numbers
5.
WEISS: 3a2b0c= 1/3:1/2:1/0. x6 = 6/3:6/2:6/0 = (230)
[Zones]
Group of faces that are parallel to a common line. 1 face can belong to more than 1 zone.
Forms
Collection of faces related by symmetry.
1. Open: do not completely enclose a space. A pyramdal prism. Open space between two parallel faces.
2. Closed: completely enclose. A dipyramidal prism. Closed space betweeen 6 opposing faces of a cube
List of forms in pg 172
Chem Basics
- Oxygen and Si are 74% of crust
- Al, K, Fe, Ca, Na, Mg are 24%
- O and Si are 67% of mantle
- Mg is 23%
- Only 83/118 elements avail to make xerals
- Isotopes: variable neutrons in atom
Pauli Exclusion Principle
No two electrons in an atom can have the same quantum state
Quantum State:
* n=position of orbit,
* l=total angular momentum: distinguishes subshells w/ different shapes (n-1) (spdf),
* ml=magnetic momentum (2l+1),
* ms=spin each orbital can contain 2 electrons that are distinguished by their spin
Ions
Atoms with more PROtons (cations) give electrons to atoms with more electrons (anions: groups 16-18).
Ionization
- Potential to lose a valence. The higher, the easier it is to lose an e. Na=high, Cl=low
- Energy necessary to remove a specific valence
- Electronegativity measures the ability of an atom in a xtal structure to attract electrons to its outer shell
Bonds
- Ionic donation of e- (NaCl, Fe3O4, Fe2O3)
- ^ moderate to high melting point
- Soluble in water/acid
- low to moderate hardness
- Brittle, perfect cleavage
- High Symm
- Transluscent
- Covalent sharing when orbitals of 2 atoms overlap (diamonds
- ^ very strong bonds
- High melting point
- high hardness
- brittle, variable cleavage
- poor solubility
- low symmetry
- translucent to opaque
- Metallic many atoms share the same electrons, as such e can move freely throughout structure
- ^high electrical and thermal conductivity
- variable melting points
- low-moderate hardness
- high symm
- sectile, ductile, malleable
- opaque
-
VanderWaals and Hydrogen Bonds weak, electrostatic. The OH in a lattice that makes it cleave
*
Ionic Radii
Fr is the largest.
* radii only constant if bond type constant
* Ionic size varies depending on CN
* Some ions become polarized (elongated) in one direction and no longer act as spehres
Radii Ratio
Ideal close-packing of sphere for given CN can only be achieved for a specific ionic raidus ratio (RR) between cat and an ions
RR=Cation Radius/Anion Radius
Polymorphism
When RR is on a CN boundary, PT conditions you can create different xtals from same formula.
Xerals that have identical compositions but different arrangements of atoms and bonds
* Can be used as geobarometers or geothermometers bc of their PT dependance
* Reconstructive: bonds are broken during the transformation. if PT conditions change, new structure will NOT revert back to original. METASTABLE condition. QUENCHABLE: the reaction is stopped, cannot go backwards. Energy needs to be supplied
* Displacive bonds are BENT
* Order-Dissorder distribution of cat and an in lattice affects structure. T plays the most important role
* Polytypism: the stacking pattern of lattice sheets changes
Closest Packing
Hexagonal: ABAB.
Cubic: ABCABC
* Best describes metals, sulfides, halides, some oxides
Pauling’s Rules
- Coordination Principle: Cat-An ion distances are equal to the sum of their effective ionic radii, cation CN determined by ratio of cation:anion
* RR<0.15: CN:2, .15-.22: 3, .22-.41: 4, .41-.73: 6, .73-1: 8. - Electrostatic Valence (ev) Principle: Strength of ionic (electrostatic) bond between ions is = ionic charge/CN
* Isodesmic Xtal: all bonds have same strength. High symm, simple chemical compounds (oxides, fluorides, chlorides
* Anisodemic Xtal: ev> ionic charge. Anion will be more strongly bound to central coordinating cation that it can be bonded to other structures. Lower symm, complex chemical compounds (sulphates, carbonates, phosphates)
* Mesodesmic: ev = 1/2 the charge on anions (silicates) the O in SiO2 can be equally bonded to central Si and other Si ions - Sharing of edges/faces by coordinating polyhedra is inherently unstable
- Cations of high valence and small CN tend to not share anions w other cations. Silicate minerals, do not contain SiO4 polyhedra sharing edges/faces bc then Si cations too close together.
- Parsimony: number of different components in a xtal tends to be small
1-4 Maximize the ion attractions and minimize the an-an and cat-cat repulsion
Electrostatic Neutrality
Mineral formula cancels out (no charge)
Solid Solution
Occurs in isostructural xerals where different elements (cations) sub for each other.
Mechanisms
1. Substitution
* one ion replaces another in a particlar size. Ions need to be similar sizes (+-0.15) and charges need to be equal
* (Na,Al)Al1-2SI2-3O8
2. Omission
* in some cases, leaves sites vacant in lattice.
3. Interstital
* Ions substituted into spaces that are usually vacant
Xtal Growth
- Availability, and continued avail. of elements. Incompatible elements stay in solution
- Stability of the growing mineral (ice melts at room T = unstable)
- Energy of formation must be appropriate (heat and work)
Thermodynamics
- Open and Closed and Isolated Systems
- System: Basalt, Parts: Phases (uniform, homogenous, physically distinct: XERALS) and Components (Smallest building blocks: ELEMENTS)
Gibb’s Phase Rules
Number of components in a system is constrained by the number of phases.
phases + freedom degrees = component + 2 (PT).
f = 2 means that both P and T can vary and we will remain liquid
f = 1 means only P or T can vary to be in eq
f = 0 fixed point. nothing can change
Gibbs Free Energy
Driving force of chemical rxn
G = SUM[u(chemical potential of phase) ][n(moles of phase)]
The Free Energy can be used to predict direction of rxn
deltaG = G (products) - G (reactants)
if 0 = equilibrium
if < 0 = rxn goes to right
if > 0 = rxn goes to the left
G(olivine) = n1u(Mg2SiO4) + n2u(Fe2SiO4)
Thermo
Chemical Potential
Potential for substance to undergo rxn. Total Pot. = u(products) - u (reactants)
