ERTH 2001: Classification

1
ERTH 2001 Classification

• Classification of Minerals by Chemical
  Composition
• Dana's System of Mineralogy (and its derivatives)
• ca. 15 major groups of minerals with a few
  important subgroups
• - we will see about 10 of these in the lab
• named according to dominant anion or anionic
  group
• basis for organisation of your textbook (Ch.
  12-20) and field guide
• by far the most important group is the
  silicates
• - 6 subgroups based on crystal structure
• before tackling this system, you need to know
  the basics of
• Crystal Chemistry (Nesse, Ch. 3)
• Crystal Structure (Nesse, Ch. 4)
• crystallography (Nesse, Ch. 2) will be
  dealt with a little later

2
ERTH 2001 Crystal Chemistry (Nesse, Ch. 3)

• Nature of Chemical Elements (p.39-45)
• Abundance of Elements (p.45-46)
• Chemical Bonding (p.46-52)
• Sizes of Atoms and Ions (p.53-55)

some knowledge of basic chemistry will be
assumed focus here is on aspects relevant to
minerals for help, see www.chemtutor.com (or
similar site)
3
ERTH 2001 Crystal Chemistry
Nature of Chemical Elements (Nesse, Ch. 3,
p.39-45) basic atomic structure distinctions
between atoms, ions, isotopes introduction to
the Periodic Table (...this should all be
review!)
4
ERTH 2001 Crystal Chemistry
Atomic structure
nucleus protons (1) neutrons (0)
(numerous subatomic particles not relevant here)
contains most of the mass of the atom atomic
number (Z) number of protons (constant) mass
number (A) number of protons neutrons
(varies) electron cloud electrons (-1)
arranged in shells (energy levels) and orbitals
occupies most of the space of the atom
controls chemical behaviour of atom for a
chemically neutral atom, electrons protons
Nesse, Table 3.1
5
ERTH 2001 Crystal Chemistry
Atomic structure
note that electrons do not actually follow
defined "orbits", but occupy shells (specific
energy levels ) and orbitals (probability
distributions within shells)
6
ERTH 2001 Crystal Chemistry
Geometry of some orbitals in electron subshells
(Nesse Fig. 3.1)
s
p
d
these geometries affect the orientations/types of
bonds formed
7
ERTH 2001 Crystal Chemistry
Shells, subshells, and quantum numbers (Nesse,
Table 3.2)
8 electrons filled outer shell (chemically
inert) "Octet Rule"
8
ERTH 2001 Crystal Chemistry
lt---- groups ----gt
(Nesse, inside back cover)
lt---- periods ----gt
9
ERTH 2001 Crystal Chemistry
Valence of electrons needed to fill outer
shell (8-n) all elements except noble gases have
one or more valence electrons that can be shared,
donated, or augmented so that outer shell 8
(Octet Rule) e.g., 11Na 2 8 1 20Ca 2 8
8 2 8O 2 6 17Cl 2 8 7
10
ERTH 2001 Crystal Chemistry
Valence of electrons needed to fill outer
shell (8-n) all elements except noble gases have
one or more valence electrons that can be shared,
donated, or augmented so that outer shell 8
(Octet Rule) e.g., 11Na 2 8 1 20Ca 2 8
8 2 8O 2 6 17Cl 2 8 7
1 2 -2 -1
11
ERTH 2001 Crystal Chemistry
Valence of electrons needed to fill outer
shell (8-n) all elements except noble gases have
one or more valence electrons that can be shared,
donated, or augmented so that outer shell 8
(Octet Rule) e.g., 11Na 2 8 1 20Ca 2 8
8 2 8O 2 6 17Cl 2 8 7
1 2 -2 -1 Ions electrons ? protons,
hence net ve or -ve charge anion -
electrons gt protons (-ve) accepts electrons
cation - electrons lt protons (ve) donates
electrons
12
ERTH 2001 Crystal Chemistry
Valence of electrons needed to fill outer
shell (8-n) all elements except noble gases have
one or more valence electrons that can be shared,
donated, or augmented so that outer shell 8
(Octet Rule) e.g., 11Na 2 8 1 20Ca 2 8
8 2 8O 2 6 17Cl 2 8 7
1 2 -2 -1 Ions electrons ? protons,
hence net ve or -ve charge anion -
electrons gt protons (-ve) accepts electrons
cation - electrons lt protons (ve) donates
electrons Isotopes atoms of element with
variable neutrons, hence variable mass
number (A) for given atomic number (Z)
can be stable (16O, 18O) or radioactive (235U,
238U) chemically identical to other
isotopes of same element
13
ERTH 2001 Crystal Chemistry
lt---- groups ----gt
8 electrons in outer shell
1 electron in outer shell
partially filled inner shells
lt---- periods ----gt
12 Mg 24.305
Z A
2 8 2
14
ERTH 2001 Crystal Chemistry
Electronegativity measures propensity for
an element to gain or lose
electrons Pauling scale (arbitrary)
Li 1.0 C 2.5 F 4.0
Nesse Table 3.4
15
ERTH 2001 Crystal Chemistry
Crustal Abundance of Elements
major elements (gt 1 wt) minor elements (0.1 - 1
wt) trace elements (lt0.1 wt)
everything else
16
ERTH 2001 Crystal Chemistry
Crustal Abundance of Elements
Nesse Table 3.5
17
ERTH 2001 Crystal Chemistry
Crustal Abundance of Elements
Nesse Table 3.6
8 major elements (gt1 by weight) O gtgt Si gtgt Al gt
Fe gt Ca gt Na K Mg
18
ERTH 2001 Crystal Chemistry
Valence of electrons needed to fill outer
shell (8-n) all elements except noble gases have
one or more valence electrons that can be shared,
donated, or augmented so that outer shell 8
(Octet Rule) e.g., 11Na 2 8 1 20Ca 2 8
8 2 8O 2 6 17Cl 2 8 7
1 2 -2 -1 Ions electrons ? protons,
hence net ve or -ve charge anion -
electrons gt protons (-ve) accepts electrons
cation - electrons lt protons (ve) donates
electrons Chemical Bonds electrons
transferred/shared between atoms to form a
stable (polyatomic) molecule, compound, or
crystal bonds involving valence electrons
(stronger) ionic, covalent, metallic other
bonds (weaker) hydrogen, van der Waals
19
ERTH 2001 Crystal Chemistry
Chemical bonds Ionic electrons transferred
from one atom to another donated (cation, e.g.,
Na) or accepted (anion, e.g., Cl-)
-


NaCl (halite)
-
note that resulting anion is much larger than the
cation
20
ERTH 2001 Crystal Chemistry
Chemical bonds Covalent electrons shared
between atoms (e.g., F2)
covalent bonds are relatively strong result is a
molecule many different types not considered in
detail here
21
ERTH 2001 Crystal Chemistry
Chemical bonds Covalent electrons shared
between atoms (e.g., F2)
Lewis structure
CH3OH (methanol) electron density map
CH4 (methane) models of bonding
22
ERTH 2001 Crystal Chemistry
Chemical bonds Metallic electrons delocalised
(e.g. Cu)
delocalised electrons
band theory electrons delocalised (mobile)
within outer conduction band
23
ERTH 2001 Crystal Chemistry
Chemical bonds Ionic electrons transferred
from one atom to another donated (cation, e.g.,
Na) or accepted (anion, e.g., Cl-) Covalent
electrons shared between atoms (e.g.,
F2) Metallic electrons delocalised (e.g.
Cu) Other bonds related to polarity of
molecules hydrogen
H2O strongly polar
resulting hydrogen bond
24
ERTH 2001 Crystal Chemistry
Chemical bonds Ionic electrons transferred
from one atom to another donated (cation, e.g.,
Na) or accepted (anion, e.g., Cl-) Covalent
electrons shared between atoms (e.g.,
F2) Metallic electrons delocalised (e.g.
Cu) Other bonds related to polarity of molecules
or structures hydrogen results from polarity of
H2O and similar molecules van der Waals
structure of graphite (C) sheets of covalently
bonded carbon atoms (strong) linked by
electrostatic forces (weak)
Nesse Fig. 3.12
25
ERTH 2001 Crystal Chemistry (Nesse, Ch. 3)

• Nature of Chemical Elements (p.39-45)
• Abundance of Elements (p.45-46)
• Chemical Bonding (p.46-52)
• Sizes of Atoms and Ions (p.53-55)

some knowledge of basic chemistry will be
assumed focus here is on aspects relevant to
minerals for help, see www.chemtutor.com (or
similar site)
26
ERTH 2001 Crystal Chemistry
Chemical bonds Ionic electrons transferred
from one atom to another donated (cation, e.g.,
Na) or accepted (anion, e.g., Cl-) Covalent
electrons shared between atoms (e.g.,
F2) Metallic electrons delocalised (e.g.
Cu) Other bonds related to polarity of molecules
or structures hydrogen results from polarity of
H2O and similar molecules van der Waals result
from weak electrostatic charges
27
ERTH 2001 Crystal Chemistry
Bonding in Minerals
most minerals have bonds intermediate
between covalent ionic or covalent
metallic
ionic character - function of electronegativity
difference between anion and cation (? a - ?
c) most cation-anion bonds in minerals involve
oxygen (? 3.5) Si-O bonds 50 ionic K-O
bonds 80 ionic 2 main types of covalent
bonds s - orbitals overlap end-to-end -
electrons localised high degree of symmetry p -
orbitals overlap side-to-side - electrons
can migrate relatively freely combinations also
possible (hybrid bonds)
28
ERTH 2001 Crystal Chemistry
purely ionic
Electronegativity
ionic character reflects electronegativity
difference between anion and cation (? a - ? c)
purely covalent
Nesse Fig 3.10
Nesse Table 3.4
29
ERTH 2001 Crystal Chemistry
Bonding in Minerals
most minerals have bonds intermediate
between covalent ionic or covalent
metallic
metallic bonding is favoured by - weakly held
valence electrons - large number of valence
electrons - availability of vacant energy levels
type of bonding is expressed in some important
physical properties e.g., hardness, ductility,
conductivity geometry of bonding is reflected in
crystal structures and symmetry e.g.,
tetrahedral C in diamond (covalent s bonds)
30
ERTH 2001 Crystal Chemistry
Bonding in Minerals halite
(NaCl) ionic compound, cubic
structure
attractive force (FA)
Na
Cl-
Na
Cl-
repulsive force (FR)
stable distance between Na and Cl- where net
(F) 0 2.8 ?
Nesse Fig. 3.4
31
ERTH 2001 Crystal Chemistry
Bonding in Minerals various forms
(polymorphs) of C properties depend on
types of bonds
Nesse Fig. 3.5
s covalent bonds diamond (H 10)
32
ERTH 2001 Crystal Chemistry
Bonding in Minerals various forms
(polymorphs) of C properties depend on
types of bonds
Nesse Fig. 3.5
s covalent bonds diamond (H 10)
graphite (H 1) s p covalent bonds (strong)
within plane sheets van der Waals bonds (weak)
between planes flakes
Nesse Fig. 3.6
33
ERTH 2001 Crystal Chemistry
Bonding in Minerals
most minerals have bonds intermediate
between covalent ionic or covalent metallic
halite
corundum
silicates - oxides - halides
olivine
sphalerite
galena
sulphides - sulphosalts
diamond
copper
molybdenite
Nesse Fig. 3.9
34
ERTH 2001 Crystal Chemistry
Stoichiometry stable compounds (e.g.,minerals)
are chemically neutral ve charges -ve
charges e.g., NaCl SiO2 KAlSi3O8
35
ERTH 2001 Crystal Chemistry
Stoichiometry stable compounds (e.g.,minerals)
are chemically neutral ve charges -ve
charges e.g., NaCl SiO2 KAlSi3O8
1 -1 4
2(-2) 1 3 3(4) 8(-2) balanced
reactions among compounds (/- ions) also
maintain overall charge balance KAl3Si3O10(OH)2
SiO2 KAlSi3O8 Al2SiO5 H2O
36
ERTH 2001 Crystal Chemistry
Stoichiometry stable compounds (e.g.,minerals)
are chemically neutral ve charges -ve
charges e.g., NaCl SiO2 KAlSi3O8
1 -1 4
2(-2) 1 3 3(4) 8(-2) balanced
reactions among compounds (/- ions) also
maintain overall charge balance KAl3Si3O10(OH)2
SiO2 KAlSi3O8 Al2SiO5 H2O you must become
familiar with valance (nominal atomic charge or
oxidation state) of geochemically abundant
elements
37
ERTH 2001 Crystal Chemistry
Crustal Abundance of Elements
Nesse Table 3.6
8 major elements (gt1 by weight) O gtgt Si gtgt Al gt
Fe gt Ca gt Na K Mg
38
ERTH 2001 Crystal Chemistry
Stoichiometry complete the following
chemical formulas by adding the appropriate
subscripts after the chemical symbols
quartz Si
O K-feldspar K Al Si
O Ca-plagioclase Ca Al Si O Mg-olivine
Mg Si O muscovite K Al
Si O (OH) corundum Al O
hematite Fe O magnetite
Fe O
39
ERTH 2001 Crystal Chemistry
Stoichiometry complete the following
chemical formulas by adding the appropriate
subscripts after the chemical symbols
quartz Si
O2 K-feldspar K Al Si
O8 Ca-plagioclase Ca Al Si O8 Mg-olivine
Mg Si O4 muscovite K Al
Si O10(OH)2 corundum Al
O3 hematite Fe
O3 magnetite Fe O4
40
ERTH 2001 Crystal Chemistry
Stoichiometry complete the following
chemical formulas by adding the appropriate
subscripts after the chemical symbols
quartz
SiO2 K-feldspar K AlSi3O8 Ca-plagiocl
ase CaAl2Si2O8 Mg-olivine
Mg2SiO4 muscovite K
Al3Si3O10(OH)2 corundum
Al2O3 hematite
Fe2O3 magnetite Fe3O4
41
ERTH 2001 Crystal Chemistry
Sizes of Atoms and Ions atomic radius
(measured in ?) reflects of
electron shells - high Z gtgt low Z
electronegativity - low ? gt high ?
chemical environment - bond length
oxidation state - anions gtgt cations
co-ordination number (CN) - high CN gtgt low CN
42
ERTH 2001 Crystal Chemistry
Sizes of Atoms and Ions atomic radius
(measured in ?) reflects of electron shells
- high Z gtgt low Z electronegativity - low ? gt
high ?
within groups
low ?
high ?
high Z
low Z
43
ERTH 2001 Crystal Chemistry
Sizes of Atoms and Ions atomic radius
(measured in ?) reflects
chemical environment - bond length
44
ERTH 2001 Crystal Chemistry
Sizes of Atoms and Ions atomic radius
(measured in ?) reflects oxidation
state - anions gtgt cations co-ordination
number (CN) - high CN gtgt low CN
high CN
anions
cations
low CN
45
ERTH 2001 Crystal Chemistry
Sizes of Atoms and Ions atomic radius
(measured in ?) reflects oxidation
state - anions gtgt cations co-ordination
number (CN) - high CN gtgt low CN
high CN
anions
what is CN?? see Nesse Ch. 4
cations
low CN
46
ERTH 2001 Crystal Chemistry
Ionic Potential charge / radius (z/r) -
important in mineral chemistry and structure -
influences the type of cation bonding with
oxygen - influences substitutions in the crystal
lattice - determines many geochemical properties
of elements e.g., ionic potential lt 2 (low
field strength) - elements tend to be
geochemically mobile ionic potential gt
2 (high field strength) - elements tend to be
geochemically immobile
47
ERTH 2001 Lab 2 Preparation
Plotting mineral compositions in triangular
diagrams (the first of 3 exercises)
Y
a) plot the compositions of the following
(hypothetical) minerals X X2Y XYZ2
b) what is the weight X in each? (at wt X
40 Y 20 Z 30)
Z
X
48
ERTH 2001 Lab 2 Preparation
Plotting mineral compositions in triangular
diagrams (the first of 3 exercises)
Y
a) plot the compositions of the following
(hypothetical) minerals X X2Y XYZ2
b) what is the weight X in each? (at wt X
40 Y 20 Z 30)
work out total atoms each
atom plot in diagram
Y
lines of constant X
X
lines of constant Z
lines of constant Y
Z
X
Z
49
ERTH 2001 Lab 2 Preparation
Plotting mineral compositions in triangular
diagrams (the first of 3 exercises)
Y
a) plot the compositions of the following
(hypothetical) minerals X X2Y XYZ2
b) what is the weight X in each? (at wt X
40 Y 20 Z 30)
work out total atoms each
atom plot in diagram
Y
X
X 100 X X2Y 67 X, 33 Y XYZ2 25 X, 25
Y, 50 Z atomic !!!!
Z
X
Z
50
ERTH 2001 Lab 2 Preparation
Plotting mineral compositions in triangular
diagrams (the first of 3 exercises)
Y
a) plot the compositions of the following
(hypothetical) minerals X X2Y XYZ2
b) what is the weight X in each? (at wt X
40 Y 20 Z 30)
work out total atoms each
atom plot in diagram
Y
X
X 100 X X2Y 67 X, 33 Y XYZ2 25 X, 25
Y, 50 Z atomic !!!!
Z
X
Z
51
ERTH 2001 Lab 2 Preparation
Plotting mineral compositions in triangular
diagrams (the first of 3 exercises)
Y
a) plot the compositions of the following
(hypothetical) minerals X X2Y XYZ2
b) what is the weight X in each? (at wt X
40 Y 20 Z 30)
work out total atoms each
atom plot in diagram
Y
X
X 100 X X2Y 67 X, 33 Y XYZ2 25 X, 25
Y, 50 Z atomic !!!!
Z
X
Z
52
ERTH 2001 Lab 2 Preparation
Plotting mineral compositions in triangular
diagrams (the first of 3 exercises)
Y
a) plot the compositions of the following
(hypothetical) minerals X X2Y XYZ2
b) what is the weight X in each? (at wt X
40 Y 20 Z 30)
work out total atoms each
atom plot in diagram
Y
X
X 100 X X2Y 67 X, 33 Y XYZ2 25 X, 25
Y, 50 Z
Z
X
Z
53
ERTH 2001 Lab 2 Preparation
Plotting mineral compositions in triangular
diagrams (the first of 3 exercises)
Y
a) plot the compositions of the following
(hypothetical) minerals X X2Y XYZ2
b) what is the weight X in each? (at wt X
40 Y 20 Z 30)
work out total atoms each
atom plot in diagram
Y
work out molecular wt wt X
X
X 100 X X2Y 67 X, 33 Y XYZ2 25 X, 25
Y, 50 Z
X 100 X X2Y 80 X XYZ2 33 X weight !!!!
Z
X
Z