Chapter 7 Basic Mineralogy
Mineral: a
naturally occurring,
inorganic
substance with a
characteristic
internal structure
and a chemical
composition that is
either fixed or
varies within
certain limits.
http://www.oum.ox.ac.uk/thezone/minerals/in
dex.htm
Ta ble 7-1. Mineral cl asses
Class
Chemical characteristics
Examples
Borates
Vario us elements in co mbination with boron
Borax [Na2 B4 O 7 
10H 2 O]
Carb onates
Metals in co mbination with carb onate
2
( CO 3 )
Calcite [CaCO 3 ]
Cerrusite [Pb CO 3 ]
Halides
Alkali metals or alkaline earths in
co mbination with halogens (F, Cl, Br, I)
Halite [NaCl]
Fluorite [CaF 2]
Hydro xides
Metals in co mbination with hyd ro xyls (OH -)
Brucite [Mg(OH) 2]
Native elements
Pure co mpound of a metallic or non metallic
element
Gold [Au]
Graphite [C]
O xid es
Metals in co mbination with o xygen
Hematite [Fe 3O 4 ]
Phosphates, arsenates,
vanadates, chro mates,
tungstates & molybdates
Vario us elements in co mbination with the
ZO 4 radical where Z = P, As, V, Cr, W , M o
Apatite [Ca5 (PO 4 )3 (F,Cl,OH)]
Carnotite [K 2(UO 2 (VO 4) 2 
3H 2 O]
Scheelite [CaWO 4 ]
Silicates
Metals in co mbination with silica tetrahedra
4
( SiO4 ) for ming three d imensional
networks, sheets, chains and isolated
tetrahedra
Quartz [SiO 2 ]
Forsterite [MgSiO 4]
Orthoclase [KAlSi 3O 8 ]
Sulfates
Alkaline earths or metals in co mbinatio n with
2
sulfate ( SO 4 )
Barite [BaSO 4 ]
Epso mite [MgSO 4 
7 H 2O]
Sulfides
One or more metals in co mbination with
Pyrite [FeS2 ]
reduced sulfur or chemically similar elements Galena [PbS]
(As, Se, Te)
Skutterudite [CoAs3 ]
Ionization potential: a measure of the energy required to
remove an electron from an atom and place it at an infinite
distance from the nucleus.
Electronegativity: a measure of the ability of an atom to
attract electrons. (The smaller the electronegativity, the less
likely the atom will attract electrons—it will most likely donate
them instead.)
A Measure of electronegativity of elements as seen
in the periodic table.
Ta ble 7-2 . Electroneg ati vities
Ion
Electronegativity
Z
Ion
Electronegativity
1
H+
2.2 0
33
As5 +
2.18
3
+
Li
0.9 8
34
Se
4
Be2+
1.5 7
35
Br -
5
B
3+
C
4+
7
N
5+
3.0 4
8
O2 -
3.4 4
9
-
Z
6
11
F
2.0 4
2.5 5
3.9 8
+
Na
2+
12
Mg
13
Al 3+
14
4+
15
16
Si
P
5+
S
2-
0.9 3
3.1 6
0.8 2
Sc
1.0 0
1.3 6
41
42
Nb
Mo
46
Pd
Ag
48
Cd
2+
49
In 3 +
47
50
51
Sn
2+
Sb
5+
2-
1.5 4
52
Te
V3 +
1.6 3
53
I-
25
Mn
26
Fe2+
27
28
29
Co
Ni
2+
2+
Cu
+
1.6 6
55
58
3+
30
Zn
1.6 5
31
Ga 3+
1.8 1
32
4+
2.0 1
60
Ce
Pr
3+
Nd
3+
69
70
1.25
3+
---
Tm
Yb
1.24
3+
71
Lu
3+
1.0
72
Hf 4+
1.3
73
5+
1.5
6+
1.7
7+
1.9
74
Ta
W
2.10
75
Re
2.2
76
Os 6 +
2.2
77
6+
2.2
2.28
2.20
1.93
78
79
Ir
4+
2.2
Au
+
2.4
2+
1.9
Pt
1.69
80
Hg
1.78
81
Tl 3 +
1.8
82
2+
1.8
3+
1.9
4+
2.0
2.2
1.96
2.05
83
Pb
Bi
2.1
84
Po
2.66
85
At 5+
1.10
La 3+
1.9 0
2.16
0.89
Ba
57
59
1.6
2+
56
1.9 1
0.95
Cs
1.8 3
1.8 8
0.82
+
1.5 5
2+
Ge
2+
+
Ti
2+
6+
2+
Rh
23
Cr
1.23
Er3 +
1.33
22
24
Ho
68
1.22
4+
3+
67
2.96
Y
45
Cl
2.55
Zr 4+
2+
K+
1.22
3+
40
Ru 2 +
1.9 0
Dy 3+
39
5+
Electronegativity
Ion
65
3+
Tc
19
21
Sr
44
2.5 8
3+
2+
43
17
Ca
Rb
1.6 1
-
20
38
+
1.3 1
2.1 9
2+
37
2-
Z
0.79
1.12
1.13
1.14
87
+
Fr
0.7
88
Ra
2+
0.9
89
Ac3+
1.1
90
4+
1.3
4+
1.5
91
92
Th
Pa
U
6+
62
3+
3+
Sm
1.17
93
Np
64
Gd 3 +
1.20
94
Pu 4+
1.7
1.3
1.3
Ta ble 7-3. Percent ionic character of a single chemical bon d
Difference in
electronegativity
Ionic
character, %
Difference in
electronegativity
Io nic
character, %
0.1
0.5
1.7
51
0.2
1
1.8
55
0.3
2
1.9
59
0.4
4
2.0
63
0.5
6
2.1
67
0.6
9
2.2
70
0.7
12
2.3
74
0.8
15
2.4
76
0.9
19
2.5
79
1.0
22
2.6
82
1.1
26
2.7
84
1.2
30
2.8
86
1.3
34
2.9
88
1.4
39
3.0
89
1.5
43
3.1
91
1.6
47
3.2
92
http://skywalker.cochise.edu/wellerr/mineral/fluorite/fluoriteL.htm
Example 7-1
The mineral fluorite has the chemical composition CaF2.
Calculate the ionic character of the bond between Ca-F.
From Table 7-2, the difference in electronegativity
= 3.98 (F-) -1.00(Ca2+) = 2.98
From table 7-3, the bond is ~89% ionic.
http://web.arc.losrios.edu/~borougt/MineralogyDiagrams.htm
Coordination number: the number of
anions that surround a cation in an
ionic crystal.
Radius ratio: the radius of the cation
divided by the radius of the anion.
So, we seem to think that silica (SiO44-) has a coordination
number of 4. Let’s test this.
From appendix III, the ionic radius of Si4+ = 0.48 & O2- = 1.32.
Then Rc/Ra = 0.48/1.32 = 0.36. If we were to check the
corresponding radius ratios from figure 7-2, we would see that it
fits nicely in the tetrahedral arrangement with a coordination
number of 4. Of course, we already knew that one!
Forsterite: Mg2SiO4
http://www.minerals.net/Image/5/97/Olivine.aspx
The Unit cell is the basic building block for a crystal. In order to
understand this concept, think of the unit cell as being like a
brick in a wall (if the wall is built by stacking bricks directly
upon one another).
X-ray Crystallography: the science of determining the
arrangement of atoms within a crystal from the manner in which
a beam of X-rays is scattered from the electrons within the
crystal. The method produces a three-dimensional picture of the
density of electrons within the crystal, from which the mean
atomic positions, their chemical bonds, their disorder and sundry
other information can be derived.
Bragg’s Law describes
the relationship between
the angle of the incident
monochromatic x-ray
beam and the diffracted
ray as a result of the
crystalline structure and
interplanar spacing.
nl = 2dsinq
A-C is the interplanar
spacing and is equal to d.
l is the wavelength of the
x-ray and q is the angle of
incidence and diffraction.
X-ray Diffraction Pattern for Forsterite Mg2SiO4.
http://www.mindat.org/min-1584.html
& Fluorite CaF2
http://www.ccp14.ac.uk/poster-talks/phase-id-1999/html/phaseid.htm
Silica
(SiO4)
O
Si
O
O
O
olivine
Examples of silicate minerals
epidote
augite
beryl
hornblende
muscovite
quartz
Mineral pictures from: mindat.org
Quartz Varieties
Pink (Rose) : due to traces of iron, manganese or titanium.
Amethyst : Maybe be manganese but some believe it could be
organic, iron or even aluminum.
Citrine : iron
Aventurine : inclusion of green mica (fushite)
Tiger's eye : inclusion of fiber of silicified crocidolite (variety of
asbestos)
Prasiolite : Iron or copper
Milk quartz : gas and liquid inclusions
Smoky : Radioactivity on quartz containing aluminium
Blue : pressure.
Chalcedony is a variety of quartz with micro-crystals. Agate is a
multicolor variety of chalcedony and onyx is a variety of agate with
parallel strips of various nuances of black.
Ionic Substitutions
When minerals crystallize, certain minor or trace elements that
are present in the environment can enter the structure of
the crystallizing mineral. There are four rules that predict,
with many exceptions, the uptake of trace elements by
crystallizing minerals.
1. Ions of one element can substitute for those of another in a crystal
structure if their radii differ by less than ~15%.
2. Ions that differ by one charge unit substitute readily for each other as
long as charge neutrality is maintained.
3. When two ions occupy the same site in a crystal structure, the ion with
the higher ionic potential preferentially enters the site.
4. Even if the size and charge of the minor and major ion are similar,
substitution may be limited for the minor ion if it has a very different
electronegativity and forms a bond of very different character from that
of the major ion.
Clay Minerals and Surface Ion Exchange
Clay mineral – fine-grained hydrous silicate composed of layers of
tetrahedrally and octahedrally coordinated cations
Figure 7-5. Structure of the octahedral and tetrahedral layer.
Mg2+ in the octahedral layer = brucite. Al3+ in the octahedral
layer = gibbsite. Al3+ can substitute for Si4+ in the tetrahedral
layer.
Clays – any particle less than 2 microns in size. May or may not be clay mineral
General clay types
Kaolinite, illites, smectites, vermiculite
Kaolinite – 1 tetrahedral and 1 octachedral layer (1:1)
-Limited subsitution of Al in the basic formula (Al2Si2O5(OH)4)
-net surface charge minimal, negligible CEC
Illite – 2 tetrahedral and 1 octachedral layer (2:1) ….the octahedral sandwich
-Al substitution for Si in tetrahedral layer
-marginal net surface charge minimal, low CEC
Smectites – also a 2:1 clay
-lots of Fe and Mg substitutions for Al in octahedral layer
-lots of Al substitution for Si in the tetrahedral layer
-swelling clay
-significant net surface charge, high CEC
Vermiculites – also 2:1 clay
-higher net surface charge
-high CEC
1:1 Clays: consist of tetrahedral layer and an octahedral layer;
substitutions are limited and the net charge is minimal (have a
low CEC.)
kaolinite
2:1 clays: consists of two tetrahedral layers with an intervening
octahedral layer. The octahedral layer can be either di- or trioctahedral and a large variety of substitutions are possible. 2:1
clays have a greater variation with net charge possibilities and
generally have a greater C.E.C.
montmorillonite
The octahedral and tetrahedral layers are arranged in different ways with
different amounts of elemental substitutions to produce different clay minerals.
T a ble 7 - 5 . S u m m a ry o f t h e pr inc i pa l c ha r a ct er is tics o f t he la y e re d cla y m ine ra l g ro u ps*
Ka olinites
Illites
S mectites
Ve rmiculites
Structure
T etrahed ra l:
Octa hedral
1:1
2:1
2:1
2:1
Octa hedral layer
Di-octahe dra l
M ostly diocta hedral
Di- or triocta hedral
M ostly triocta hedral
Inte rlayer c ations
Nil
K
Ca , Na
Mg
Inte rlayer water
Only in ha lloysite
So me in
hydro muscovite
Ca , two la yers
Na, o ne to many
layers
Ca , two la yers
K, one la yer to nil
Basal spacing
7.1 
10 
Va ria ble
most ~ 15 
Va ria ble
14.4  whe n fully
hydrated
Ethylene glycol
Only taken up by
halloysite
No effect
T wo glyc ol laye rs,
17 
One glycol layer,
14 
Ca tion e xchange
ca pacity (CE C) in
meq/100 g c lay
Nil
3 - 15
Low
10 - 40
High
80 - 150
High
100 - 150
Formula
Al 2Si 2 O 5(OH) 2,
little variation
K 0 .5-0.7 5Al 2(Si,A l)2
O 10 (OH) 2
M +0 .7( Y3+ , Y2+ ) 4-6
(Si,Al) 8O 2 0(OH) 4 
n
H2 O
M 2+ 0.66 (Y 2+ , Y3+ ) 6
(Si,Al) 8O 2 0(OH) 4 
8
H2 O
Dilute ac ids
Scarce ly soluble
Re adily a ttacke d
Attac ked
Re adily a ttacke d
E xcept halloysite,
uncha nged
No ma rke d c hange
Colla pse to
appro xi mate ly 10

E xfolia tion,
shrinka ge of layer
spacing
Ka olinite, dickite ,
nac rite , ha lloysite
Illite , hydrous
micas , phengite ,
bra mmallite,
glauc onite,
ce ladonite
M ontmo rillonite ,
beide llite,
nontronite,
hec torite , saponite,
sauconite
Ve rmiculite
Hea ting 200
E xa mples
o
C
*M odified fro m Dee r et al. (1992)
Clays will have negative net surface charge caused by:
1) Subsitutions ….Al3+ for Si4+ in tetrahedral layer, Mg2+ for Al3+ in octahedral layer
2) Imperfections in crystal structure (e.g. missing cations)
3) Broken bonds at edges of crystals (exposing O2- or OH- ions)
For the 2:1 clays surface charge arises mostly from substitutions and imperfections
For 1:1 clays surface charge arises mostly from broken bonds at crystal edges
Ta ble 7-7. P er man en t n egati ve s ur face ch arge of 2:1 c lay min er als11
M ineral group
1
2
Charge ( mol sites kg -1) 2
Kaolinite
0.02 - 0.2
Illites
0.1 - 0.9
S mectites
0.7 - 1.7
Vermiculites
1.6 - 2.5
Data fro m Sposito (1989), Lang muir (1997)
Charge in moles of monovalent sites per kg of clay
What is Cation Exchange Capacity (CEC) and why is it important?
http://www.finerminds.com/health-fitness/vitaminwater-not-healthy/
http://www.finesttreeserviceaz.com/
http://fernroadfarm.blogspot.com/
Cation Exchange Capacity
The net negative surface charge will attract (adsorb) ambient dissolved cations
If other cations are introduced, these adsorbed cations will be replaced by the
new cations to varying degrees ….cation exchange
The cation exchange capacity (CEC) will vary from clay to clay depending on
clay structure, amount and type of substitution, pH, and particle surface area
CEC – specifically defined as the uptake or release of ammonium (NH4+) ions
when the clay is exposed to a 1 M ammonium acetate solution at pH 7.0
Units for CEC = meq / 100g
CEC(meq/100g) = NSM(mole sites/g)x105
If surface has a net positive charge then the AEC (anion exchange capacity) is
measured
Surface area effects
-3
Ta ble 7-8. S u rface ar ea pe r u n it mas s of illite w ith a de ns ity of 2600 k g m-3
Nu mber of cubes
Surface area of cube ( m2)
Su rface area (m2 g -1)
1
6
2.3 x 10 -6
1 x 10 -2 (cm)
1 x 10 6
6 x 10 -4
2.3 x 10 -4
1 x 10 -6 (1 µ m)
1 x 10 1 8
6 x 10 -12
2.31
1 x 10 -7 (0.1 µ m)
1 x 10 2 1
6 x 10 -14
2 3.1
1 x 10 -8 (0.01 µ m)
1 x 10 2 4
6 x 10 -16
231
Length of side ( m)
1
clay particles have
a large surface to
mass ratio
The number of negative surface sites per area (NSA) is related to the surface area
(SA),and the mole sites per unit mass (NSM)
NSA = NSM / (1.66 E-6) (SA)
And the NSM is used to calc CEC
CEC = NSM (1.0 E5)
units
NSA – sites nm-2
NSM – mole sites g-1
SA – m2g-1
CEC – meq 100g-1
Example 7-6: Given a smectite with a negative surface charge of 0.8 mole sites kg-1,
what is the CEC?
CEC= (0.8 mole sites kg-1 ) (.001 kg g-1) (1 E5) = 80meq 100g-1
Determining ion-exchange properties
Batch method
Start with solution of known cation conc., ionic strength, and pH
Add clay
Compare cation conc. before and after addition of clay
Repeat at different pHs, ionic strengths, cation concentrations
Use data to construct adsorption isotherms
Adsorption Isotherms
Represent partitioning of a particular species between an aqueous phase
and solid particles (sorbate)
Kd is the tangent to the isotherm found
at the origin
At high concentrations, precipitation
keeps the aqueous concentration
constant
Figure 7-8. Representation of a typical adsorption isotherm showing the distribution of a
species between an aqueous phase and a solid (sorbent). At very low concentrations, the
distribution behaves ideally and can be represented by a unique value, Kd. At higher
concentrations, the partitioning deviates from ideality. If precipitation occurs, the
concentration of the species in solution will remain constant; i.e., the solution is saturated
with respect to the particular species.
Column Test Method
In this case, the sorbent is packed into a column and a volume of
solution is passed through the column. The concentration of the
ion of interest in the original solution is compared to that in the
eluent and the Kd is calculated using the following formula.
Kd = ((Ci – Cf)/Cf))(V/M)
http://www.cresp.org/cresp-projects/waste-processing-special-nuclearmaterials/leaching-assessment-for-alternative-waste-forms/
Example 7-7
Ten grams of montmorillonite are placed in a column and 100ml
of solution are passed through the column. The initial solution
has a zinc concentration of 20 mg L-1 and the eluent has a zinc
concentration of 14.1 mg L-1. Calculate the Kd for zinc between
the solution and the montmorillonite.
Kd = ((20 – 14.1)/14.1))(100 cm3/10g) = 4.18 cm3 g-1
Zeolites: a crystalline structure characterized by a framework
of linked tetrahedra, each consisting of four O atoms
surrounded by a cation. This framework open cavities in the
form of channels and cages. These channels are usually
occupied by H2O, but large enough to allow the passage of
guest species. Zeolites have relatively large CEC and are
useful for a variety of environmental remediation processes.
Asbestos minerals: a group of silicate minerals that occur as
long, thin fibers. They have high tensile strength, flexibility, and
heat and chemical resistance. Asbestos minerals can be
described by two different structures: chrysotile and amphibole.
Chrysotile structure: consists
of a layer of silica tetrahedra
bonded to a layer of
octahedrally coordinated Mg
ions. Each Mg2+ is surrounded
by four hydroxyl molecules and
two oxygens. The distance
between the oxygens in the
octahedral layer is slightly
greater than the distance
between the oxygens in the
tetrahedral layer. This results in
the octahedral layer curling
around the tetrahedral layer
forming a scrolled tube.
Amphibole structure: consists of a
strip of octahedrally coordinated
cations sandwiched between two
double silica chains. The chains
extend for an infinite distance. The
cations can be Na, Li, Ca, Mn, Fe,
Mg, Al, and Ti.
Health Effects of Asbestos Exposure
Asbestosis: a lung disease caused by asbestos particles
deposited in the lungs through inhalation. Over time, the lung
encapsulates these fibers and hardens leading to a decrease
in the efficiency of the O2/CO2 exchange.
Mesothelioma: a rare, diffuse malignant cancer of the lining of
the lung and stomach. It has a long latency period of 35 to 40
years.
Lung cancer: usually linked to smoking, however, some cases
have been attributed to radon, second-hand smoke, or
exposure to asbestos.
Crystalline and Amorphous Silica
There are six polymorphs (same chemical composition, but
different crystalline structure) of silica composition with a
chemical formula of SiO2.
Amorphous silica (opal, SiO2·nH2O) is found in siliceous
oozes in the seafloor sediments and on land as preserved
deposits of marine sediments or precipitated from geyer fluids
that contain high amounts of dissolved silica.
Dissolution of Silica Minerals
SiO2(s) + 2H2O  H4SiO4(aq)
For quartz:
logKsp = 1.8814 – 2.028 x 10-3T – 1560.46 / T
For amorphous silica:
logKsp = 0.338037 – 7.8896 x 10-4T – 840.075 / T
Where T is the temperature in Kelvin.
When figuring the solubility in ppm, remember to multiply the
Ksp (in units of moles/L) by the gram-molecular weight of silica
(SiO2) regardless if you are calculating quartz or amorphous
silica.
Example 7-8
Calculate the Ksp for quartz and amorphous silica at a pH of 5.5 and
T = 25⁰C. Which form of silica is more soluble?
For Quartz:
Log Ksp = 1.8814 – (2.028 x 10-3)(298.15) – 1560.46/298.15
= -3.96 Ksp = 10-3.96
For Amorphous silica:
Log Ksp = 0.338037 – (7.8896 x 10-4)(298.15) – (840.075/298.15)
= -2.71 Ksp = 10-2.71
Amorphous silica has the larger Ksp and is the more soluble form of
solid silica.
Chapter 7 Problem set due November 26:
#s: 1, 9, 10, 14, 36, 49, 55, 57
http://agwired.com/2010/11/12/the-cost-of-thanksgiving-dinner/