Class notes Flashcards
Mineral
An element or a compound which is crystalline and which forms by geological processes
crystalline
a highly ordered atomic arrangement of atoms or ions arranged in a geometric pattern
What is the one exception to the rule that minerals must be solid?
Mercury
mineraloid
Between a glass and a mineral
crystalline materials
Elements or compounds with a definite chemical composition
May be fixed-ex quartz SiO2, or may have a composition between certain limits ex-dolomite CaMg(CO3)2
Geological processes
Implies that it is naturally occurring.
synthetic
Implies something was created in a lab, but is otherwise a mineral in all aspects ex-synthetic quartz
Biogenic
biologically produced rather than geologically produced.
Is coal a mineral?
No, it was formed biogenically.
What defines a mineral?
Crystal structure, chemical composition.
crystals
planar faces
crystal form vs crystal habit
crystal form-geometric shape of a crystal. Shows symmetry (octahedron, cube, tetrahedron)
crystal habit-a general term has to do with crystal growth.
Specific gravity vs density
density is mass/volume. has units.
specific gravity-unitless density/density of water at 4 degrees celcius.
What happens when you place calcite over a dot on paper?
You see two points. This has to do with light moving through it.
The 2 major types of crystals
Molecular Crystals Nonmoleculuar crystals (Metallic, covalent, ionic)
Molecular crystals
Crystals that are made up of molecules bonded covalently within a group. Molecules are bonded together by Van Der Wall forces. (nonmetals, diatomic elements, compounds)
Van Der Walls Forces
A very weak bond.
What type of band causes crystals to become very soft?
Van Der Walls
Physical properties of minerals with Van Der Walls bonds
soft, weakly bonded between molecules, low melting point.
Induced Van Der Walls bonding
An atom will orient itself to match the other
Metallic crystals
A type of nonmolecular crystal. Made up of cations that are nearly equal in electronegativity with metal bonds.
Closest packed
Atoms cannot get any closer together. This is usually the case with metal bonds.
Metal bonds
Loosely held valenece electrons are shared between neighbors to form a bonding pair. If a cation has 12 neighbors the valence electron is shared equally so that each valence electron spends 1/12 of the time with each of the 12 neighbors.
*Orbitals become extremely close-makes transfer among orbitals easy.
Characteristics of metallic crystals due to metal bonds
bonds are non directional. This is why metals are malleable.
Types of closest packing
Cubic-ABCABCABC…
Hexagonal-ABABABAB
Physical properties resulting from closest packing
high densities, good conductors, malleable
Covalent crystals
A bond that forms so that an incompletely filled valence orbital of one atoms overlays another incompletely filled outer orbital. Produces a stable inner configuration.
Are covalent bonds directional?
Yes
What is the only crystal we know of that is completely covalent
Diamond
polymorphism
The ability of the substance to crystallize as more than 1 strucute. (ex-diamond and graphite)
Electronegativity
the abililty of an atom in a crystal structure to attract e- to it’s outer shell. This has an influence on it’s position in the periodic table.
define radius ratio
rcation/ranion
CN 12 makes what type of shape
closest packing
CN 8 makes what type of shape
cubic coordination
CN 6 makes what type of shape
octahedral
CN 4 makes what type of shape
tetrahedral
CN 3 makes what type of shape
planar triangular
CN 2 makes what type of shape
linear
Ionic radii
Bond length is the center to center distance between 2 atoms.
variations in ionic radii depend on
The percentage of ionic covalent and metallic bonds, and the number of nearest neighbors (the CN)
Goldschmidt’s rule
A cation can not rattle around in it’s coordination until without the anions.
Pauling’s first rule
A coordination polyhedron of anions is formed about each cation.
Pauling’s second rule
An ionic structure will be stable to the extent that the sum of the strengths of the electrostatic bonds that reach an anion form adjacent cations equals the charge on that anion.
Electrostatic bond strength=
valence charge/CN
Pauling bond strength=
charge/CN
2 things we can look at that indicate bond strength according to Pauling’s rules
Bond distance, charge neutrality
Pauling’s thrid rule
The sharing of edges, particularly of faces by 2 anion polyhedra decreases the stability of an ionic structure
Pauling’s 4th rule
In a crystal structure containing different cations thos of high valency and small C.N. tend not to share polyhedral elements with eachother
Pauling’s 5th rule
The number of essentially different kinds of constituents in a crystal tends to be small.
Why is Pauling’s 5th rule?
There are not many different types of strucutres so that they fit together easily.
Isostructuralism
2 or more compounds whose atoms are arranged in the same type of crystal structure.
The 2 types of structural imperfections
Mosaic crystals-A single crystal that consists of a mosaic of slightly misoriented blocks.
Lineage structure-Has a nucleus of long arms. These arms branch and twist slightly and are misoriented.
Point defects
Schottky-an accidental vacancy
Frenekl-an atom mislocation
Line defects (dislocations)
Edge dislocation-a plan feature of atoms that end of terminate in the structure.
screw dislocation-a block of atoms with a screw axis that aids in crystal growth. Blocks of atoms adhere to edges much better than to a single surface.
Edge dislocation
a planar feature of atoms that end or terminate in the structure
screw dislocation
A block of atoms with a screw axis that sids in crystal growth. Blocks of atoms adhere to edges much better than to a single surface.
solid solutions
Specific atom sites are occupiedin variable proportions by 2 or more defecit elements.
How do atom or ionic sizes control solid solutions?
size difference
End members of olivine
Fosterite: Mg2SiO4
Fayalite: Fe2SiO4
An example of a substitutional solid solution
Olivine
Substitutional solid solution
Represents a 1:1 replacement. Implies that there are 2 independent sites each accepting either ion on a random basis.
A coupled solution
2 ions work together to substitute for charge neutrality.
An example of coupled substitution, and the end members.
Feldspar-plagioclase
Albite- NaAlSi3o
Anortherite: CaAl2Si2O8
Intersital solid solution
Open spaces for interstital cations or molecules.
-Open Chanels
ex-Beryl
Omissional solid solutions
occurs when a highly charged cation replaces 2 or more cation for charge balance.
ex-microline
___ plus Pb^2plus goes to 2Kplus
How can you tell the difference between a wet chemical analysis and microprobe?
If it can tell the difference between Fe2plus and Fe3plus.
How does a microprobe work?
Take a mineral grind and polish the top of a mineral, put it in an electron gun, bombard the surface of plate with electrons, electrons go in and x-rays come out. Look at the energy of the x-rays, and then you can figure out what element you have.
