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1. q 2003 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org.
Geology; September 2003; v. 31; no. 9; p. 737–740; 1 figure; Data Repository item 2003109. 737
An earth scientist’s periodic table of the elements and their ions
L. Bruce Railsback*
Department of Geology, University of Georgia, Athens, Georgia 30602-2501, USA
ABSTRACT
A new Earth Scientist’s Periodic Table of the Elements and Their Ions presents the
naturally occurring charged species commonly encountered by geoscientists, as well as
elemental forms, and it is organized by charge. The new table therefore shows many
elements multiple times, unlike the conventional table. As a result, trends, patterns, and
interrelationships in mineralogy, soil and sediment geochemistry, igneous petrology, aque-
ous geochemistry, isotope geochemistry, and nutrient chemistry become apparent in this
new table. The new table thus provides a more effective framework for understanding
geochemistry than the conventional, and purely elemental, periodic table.
Keywords: geochemistry, mantle, minerals, nutrients, seawater, weathering.
INTRODUCTION
The Periodic Table of the Elements formulated by de Chancour-
tois, Meyer, and Mendeleev (Farber, 1969; Courtney, 1999) has clearly
been of great utility in explaining and predicting relationships in chem-
istry. It has been of less utility, however, in the earth sciences. For
example, it does not arrange lithophile, siderophile, and chalcophile
elements into distinct groups, and it does not group elements into nat-
urally occurring sets (e.g., elements concentrated in the mantle, in sea-
water, or in soil). Elements critical for biological processes are likewise
not grouped in useful ways by the conventional periodic table. In these
respects, the conventional periodic table has not provided a good
framework for understanding the chemistry of Earth and its life.
Application of the conventional periodic table of the elements to
the earth sciences has been disadvantaged because most matter at or
near Earth’s surface is not in elemental form. Instead, most atoms of
the matter encountered by earth scientists carry charge. Si is a very
good example: every earth scientist has encountered Si as Si41
, where-
as few earth scientists are even aware that a very small amount of
natural elemental Si is known to exist (Gaines et al., 1997). The use-
fulness of any document summarizing chemistry for the earth sciences
would clearly be enhanced by inclusion of charged matter in addition
to elemental forms.
With that view in mind, this paper presents an Earth Scientist’s
Periodic Table of the Elements and Their Ions1. In this table, natural
groupings and trends in geochemistry, marine chemistry, and nutrient
chemistry become apparent, allowing a more general synthesis of the
chemistry of the earth sciences. The result is an integrated view of
geochemistry applicable from the mantle to soil to seawater. One fun-
damental concept in rationalizing these geochemical patterns is the dif-
ference in bonding exhibited by hard and soft cations, which favor O22
and S22
, respectively. The other is the extent to which charge of cations
is sufficiently focused (i.e., ionic potential is sufficiently high) to pro-
vide strong bonds to O22
without causing repulsion between those
cations. Thus bonding and coordination with oxygen, Earth’s most
abundant element in the mantle and crust (McDonough and Sun, 1995),
dictate many of the trends discussed in the following sections.
*E-mail: rlsbk@gly.uga.edu.
1GSA Data Repository item 2003109, sources of information used in con-
structing table, and explanatory notes, is available online at www.geosociety.org/
pubs/ft2003.htm, or on request from editing@geosociety.org or Documents Secre-
tary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA.
DESCRIPTION OF THE TABLE
Chemical entities are arranged according to charge in the Earth
Scientist’s Periodic Table of the Elements and Their Ions (Fig. 1)2.
Thus, B, C, and N, which are conventionally on the right side of the
periodic table, appear on the left in the left-to-right horizontal sequence
Li1
, Be21
, B31
, C41
, and N51
. Al, Si, P, and S similarly appear on the
left and within the left-to-right horizontal sequence Na1
, Mg21
, Al31
,
Si41
, P51
, and S61
. A more striking result of organizing the table ac-
cording to charge is that many elements appear multiple times, because
different natural conditions cause those elements to assume different
charges. Many elements (e.g., P and U) thus appear twice, a few appear
three times (e.g., V, Fe, C, and N), and a few appear four times (most
notably S, as S22
, S0, S41
, and S61
).
The table is broken from left to right to separate noble gases, hard
or type A cations (those with no outer-shell electrons), intermediate to
soft or type B cations (those with at least some outer-shell cations),
elemental (uncharged) forms, anions, and the noble gases again (Fig.
1). The significance of the division of cations is that hard cations bond
strongly to F2
and O22
but not to S22
, whereas the soft cations bond
strongly to S22
and the larger halides, Br2
and I2
(Stumm and Morgan,
1996) (Fig. 1, Inset 8). These patterns are exemplified in nature by the
absence of sulfide minerals of Ca21
and of the other hard cations, but
the existence of oxides and sulfates of those cations (Fig. 1). The nat-
ural occurrence of sulfides, but not oxides, of the platinum group ions
provides a converse example (Fig. 1). The differences between hard
and soft cations are further illustrated by insets 3 and 6, which show
that melting temperatures of oxides of cations of intermediate ionic
potential decrease from hard to intermediate to soft cations. Inset 8
likewise shows that the relative solubility of halide compounds can be
predicted from the division of hard and soft cations, in that solubility
of halides of hard cations increases from F2
to I2
, whereas solubility
of halides of soft cations increases from I2
to F2
. In igneous geochem-
istry, the failure of Cu1
to bond with O22
and substitute for Na1
in
plagioclase (Ringwood, 1955) provides an example of the different
behavior of soft and hard cations, respectively. The failure of Tl1
to
substitute for K1
, despite the similar size and charge of those two
cations, is another example.
Another difference between the new table and its conventional
predecessors is that the new table includes the naturally occurring ac-
2Loose insert: Figure 1. An Earth Scientist’s Periodic Table of the Ele-
ments and Their Ions. Sources of information used in constructing table and
related notes are available in Appendix DR1 in GSA Data Repository (see text
footnote one).

2. S 16
3233 34 36
r=1.84
m=32.066
Sulfur as sulfide
2– Cl 17
m=35.453
35 37
r=1.81
Chlorine
as choride
–
O 8
m=15.999
16 17 18
r=1.40
2–
Oxygen as oxide
N 7
m=14.007
14 15
r=1.71
Reduced nitrogen
3–
F 9
m=18.998
19
r=1.36
Fluorine
as fluoride
–
C 6
m=12.011
12 13 14
r=2.60
Reduced carbon
4–
78 80 82
Se
m=78.96
74 76 77
r=1.98
Selenium
34
2–
as selenide
15
m=30.974
r=2.12
Phosphorus
3–
as phosphide
P
51
r=2.45
121 123
Sb
m=121.760
Antimony
3–
as antimonide
Fe
Zr
Li
Lu
10 most abundant elements in Earth's crust
11th to 20th most abundant elements in Earth's crust
21st to 40th most abundant elements in Earth's crust
41st to 92nd most abundant elements in Earth's crust
Noble Gases
Anions
with
which
hard
cations
preferentially
coordinate
Anions
(No ionization)
Anions
with
which
soft
cations
preferentially
coordinate
Intermediate
Br 35
m=79.904
79 81 (82)
r=1.95
(7+ r=0.39)
Bromine
–
as bromide
Anions that commonly coordinate with H+
(e.g., as CH4, NH3, H2S, H2O, etc.)
z r
/
= 1
z
r
/
=
1
2
At 85
215 218 219
Astatine
Rn 86
(222)
220 222
218 219
Radon
z
r
/
=
2
Si 14
m=28.086
r=2.71
Silicon as silicide
4–
The only known natural occurrences of
phosphides and silicides are in meteorites
and cosmic dust.
As 33
m=74.922
75
r=2.22
Arsenic as arsenide
3–
Most natural occurrences of carbides and
nitrides are in meteorites or mantle phases.
He 2
3 4
Helium
m=4.0026
r=1.2
Ne 10
20 21 22
Neon
m=20.180
r=1.5
Ar 18
36 38 40
Argon
m=39.948
r=1.8
Kr 36
78 80 82
83 84 86
Krypton
m=83.80
r=1.9
Xe 54
129 130 131
132 134 136
124 126 128
Xenon
m=131.29
r=2.1
Cations that
coordinate with H2O
(or CO3
2– or SO4
2–)
in solution
Cations that coordinate with
O2– in solution (e.g., as
NO3
–, PO4
3–, SO4
2–, etc.)
Noble Gases
(No ionization)
z
/
r = 1
Rn 86
(222)
219 220 222
Radon
z
/r = 4
z/r = 2
"Hard" or "Type A" Cations
(All electrons removed from outer shell)
(Thus a noble-gas-like configuration
of the outer shell)
Coordinate F>O>N=Cl>Br>I>S
Where Fe2+
and Fe3+ would
fall if they were
hard cations
He 2
m=4.0026
3 4
Helium
r=1.2
Ne 10
m=20.180
20 21 22
Neon
r=1.5
Ar 18
m=39.948
36 38 40
Argon
r=1.8
Kr 36
m=83.80
78 80 82
83 84 86
Krypton
r=1.9
Xe 54
m=131.29
129 130 131
132 134 136
124 126 128
Xenon
r=2.1
ionic charge ÷
ionic radius
= 32 =
z
r
Cs 55
m=132.905
133
r=1.69
Cesium ion
+
Fr 87
(223)
223
r=1.76
Francium ion
(<30 g in crust)
very rare
+
137 138
Ba 56
m=137.327
130 132
r=1.35
134 135 136
Barium ion
2+
Ra 88
(226)
223 224
r=1.40
226 228
Radium ion
2+
Cations that
coordinate with OH–
or O2– in solution
z
/
r
=
1
6
?
Y 39
m=88.906
89
Yttrium ion
r=0.93
3+
Ac 89
m=227.03
r=1.18
227 228
?
Actinium ion
3+
Zr 40
m=91.224
90 91
r=0.80
92 94 96 ?
Zirconium ion
4+
Pu 94
Plutonium
Very limited
natural
on Earth
occurrence
239
Np 93
Neptunium
237 ?
Very limited
natural
on Earth
occurrence
92
234 235 238
Uranium, e.g.
*
r=0.7
m=238.029
U
as uranyl (UO2
2+)
6+
Th 90
m=232.038
227 228 230
r=0.95
(+3 r=1.14)
231 234
Thorium ion
232*
4+
Pa 91
(231)
(+4 r=0.98)
231 234
Protactinium ion
5+
Cations that
coordinate
with OH– (or
H2O) in
solution
+
Li 3
m=6.941
6 7
r=0.60
Lithium ion
Na 11
m=22.990
23
Sodium ion
r=0.95
+
K 19
m=39.098
39 40 41
r=1.33
Potassium ion
+
Rb 37
m=85.468
85 87
r=1.48
Rubidium ion
+
Be 4
m=9.012
9
r=0.31
Beryllium ion
2+
Sr 38
m=87.62
87 88
84 86
r=1.13
Strontium ion
2+
B 5
m=10.811
10 11
r=0.20
Boron
as borate (B(OH)3
3+
or B(OH)4
–)
C 6
12 13 14
m=12.011
Carbon, as CO2,
2-
& carbonate (CO3 )
4+
bicarbonate (HCO3)
-
15
r=0.
N 7
m=14.007
14 15
r=0.11
Nitrogen
as nitrate (NO3
–)
5+
P
m=30.974
31
r=0.34
Phosphorus as
5
1
phosphate (PO4
3–
5+
and HPO4
2–)
S 16
m=32.066
32 33 34 36
r=0.29
Sulfur as
sulfate (SO4
2–)
6+
Cr 24
m=51.996
50 52 53 54
r=0.52
Chromium, e.g. as
chromate (CrO4
2–)
6+
Nb 41
m=92.906
r=0.70
Niobium (or
Columbium) ion
(96)
93
5+
V 23
m=50.942
50 51
r=0.59
Vanadium ion
e.g., as vanadate
5+
96 98 100
Mo 42
m=95.94
92 94 95 97
r=0.62
Molybdenum
e.g., as molybdate
6+
Re 75
m=186.207
r=0.56
185 187
Rhenium ion
7+
Hf 72
m=178.49
174 176 177
r=0.81
178 179 180
Hafnium ion
4+
Ta 73
m=180.948
180 181
r=0.73
Tantalum ion
5+
e.g., as tantalate
r=0.68
W 74
180 182 183
184 186
m=183.84
Tungsten (Wolfram)
e.g., as tungstate
6+
Tc 43
(100)
Technetium
Very limited
natural
on Earth
occurrence
99
Elements 95 and beyond do not occur naturally:
95: Americium
96: Curium
97:Berkelium
98 Californium
99: Einsteinium
100: Fermium
101: Mendelevium
102: Nobelium
103: Lawrencium
104: Rutherfordium
105: Hahnium
"Soft" ("Type B") Cations
(Many electrons remain in outer shell)
Coordinate I>Br>S>Cl=N>O>F
z r
/
= 4
Intermediate Cations
(Some electrons remain in outer shell)
Coordination with S or O likely
z/r = 16
Po
210 211 212
216 218
214 215
84
Polonium
z
r
/ = 8
coordinate with O2– (± OH–) in solution
Cations that
3+ r= 0.64
Mn 25
4+ r=0.53
Manganese ion
3,4+
Fe 26
r=0.64
Ferric iron
3+
Co 27
r=0.63
Cobaltic cobalt
3+ Sn 50
r=0.71
Stannic tin
4+
Sn 50
m=118.710
112 114 115 116
r=1.12
120 122 124
117 118 119
Stannous tin
2+
102 104
Ru 44
m=101.07
96 98 99
3+ r=0.69
4+ r=0.67
100 101
Ruthenium ion
3,4+ Rh 45
m=102.906
r=0.86
103
Rhodium ion
2+
Pd 46
m=106.42
102 104 105
106 108 110
r=0.86
Palladium ion
2+
92
Uranium ion
r=0.97
U
4+
74
m=183.84
180 182 183
r=0.64
184 186
W
Tungsten (Wolfram)
ion
4+
Re 75
m=186.207
185 187
r=0.65
Rhenium ion
4+
190 192
Os 76
m=190.23
184 186
r=0.69
187 188 189
Osmium ion
4+
Ir 77
m=192.217
r=0.66
191 193
Iridium ion
4+ Pt 78
m=195.078
190 192 193
r=0.96
196 198
194 195
?
Platinum ion
2+
212 214
Pb 82
m=207.2
204 206 207
r=1.20
208 210 211
Plumbous lead
2+
Pb 82
r=0.84
Plumbic lead
4+
Bi 83
m=208.980
r=1.20
212 214 215
209 210 211
Bismuth ion
3+
Bi 83
r=0.74
Bismuth ion
5+
97 98 100
42
m=95.94
92 94 95 96
r=0.68
Mo
Molybdenum ion
4+
r=0.61
V 23
Vanadium ion
4+
z
/
r
=
8
As 33
r=0.47
arsenate (AsO4
3–)
5+
As 33
m=74.922
75
Arsenic
r=0.69
e.g., as arsenite
3+
r=0.62
Sb 51
e.g., as antimonate
5+
Sb 51
m=121.760
r=0.90
121 123
Antimony ion,
3+
as in antimonites
S 16
r=0.37
4+
as sulfite (SO3
2–)
Sulfur Se 34
r=0.42
as selenate (SeO4
2–)
6+
78 80 82
Se 34
m=78.96
74 76 77
r=0.50
Selenium
4+
e.g., as selenite
52
r=0.56
Te
e.g., as tellurate
6+
128 130
52
m=127.60
120 122 123
r=0.89
124 125 126
Te
Tellurium ion,
4+
as in tellurites
53
r=0.44
Iodine
I
5+
as iodate (IO3 )
–
m=126.904
4 most abundant constituents
in atmosphere
5th to 8th most abundant
*For the sake of simplicity,
232Th-208Pb series are omitted.
the 235U-207Pb and
Rare earth elements (REEs)
(effectively "Hard" or "Type A" cations in their 3+ state)
176Hf
?
No natural
occurrence
on Earth
Pm 61
(150)
?
Promethium
z/r = 2
=
i
o
n
i
c
c
h
a
r
g
e
÷
i
o
n
i
c
r
a
d
i
u
s
138Ba
Lantha-
nides:
z
/
r =
4
z
/
r
=
2
z
/
r
=
1
La 57
m=138.906
r=1.15
138 139
Lanthanum ion
3+
142
Ce 58
m=140.116
136 138 140
r=1.11
Cerium ion
3+
148 150
Nd 60
m=144.24
142 143 144
r=1.08
146 145
?
Neodymium ion
3+
Eu 63
m=151.964
151 153
r=1.03
Europium ion
3+
Gd 64
m=157.25
152 154 155
r=1.02
158 160
156 157
Gadolinium ion
3+
Tb 65
m=158.925
r=1.00
159
Terbium ion
3+ Dy 66
m=162.50
156 158
r=0.99
163 164
160 161 162
Dysprosium ion
3+
Ho 67
m=164.930
165
r=0.97
Holmium ion
3+ Er 68
m=167.26
162 164 166
r=0.96
167 168 170
Erbium ion
3+
Tm 69
m=168.934
169
r=0.95
Thulium ion
3+ Yb 70
m=173.04
168 170 171
r=0.94
(2+ r= 1.13)
174 176
172 173
Ytterbium ion
3+
Lu 71
m=174.967
175 176
r=0.93
Lutetium ion
3+
Pr 59
m=140.908
141
r=1.09
(4+ r=0.92)
Praseodymium ion
3+
r=1.01
Ce 58
Cerium ion
4+
152 154
Sm 62
m=150.36
144 147 148
r=1.04
149 150
Samarium ion
3+
Eu 63
r=1.12
Europium ion
Substitutes for Ca2+
2+
C
6
Diamond
r=0.77
& graphite
S
16
Sulfur
Si
14
r=1.34
Silicon
Se
34
Selenium
r=1.6
Cd
48
Cadmium
r=1.56
In
49
Indium
r=1.66
52
Te
Tellurium
r=1.7
Re
75
Rhenium
r=1.37
Ta
73
Tantalum
r=1.46
Gases
Non-
metals
Metals
2
N
7
nitrogen
r=0.71
Molecular
O
8
2
oxygen
Molecular
Bi
83
Bismuth
r=1.82
Pb
82
Lead
r=1.75
Cr
24
Chromium
r=1.27
Co
27
Cobalt
r=1.25
Ni
28
Nickel
r=1.24
Fe
26
Iron
r=1.26
Pd
46
Palladium
r=1.37
Rh
45
Rhodium
r=1.34
Ru
44
Ruthenium
r=1.34
Os
76
Osmium
r=1.35
Ir
77
Iridium
r=1.35
Zn
30
Zinc
r=1.39
Al
13
Aluminum
r=1.43
As
33
Arsenic
r=1.48
Sb
51
Antimony
r=1.61
Sn
50
Tin
r=1.58
Au
79
Gold
r=1.44
Ag
47
Silver
r=1.44
Pt
78
Platinum
r=1.38
Cu
29
Copper
r=1.28
Hg
80
Mercury
r=1.60
Tl
81
Thallium
r=1.71
Elemental Forms
other than noble gases
(uncharged)
Principal elements in iron
meteorites (Fe>>Ni>>Co) and,
with S or O, presumably domi-
nant elements in Earth's core
and isotopic
are omitted to
conserve space)
(Atomic masses
information
Elements that occur as native minerals, recognized in antiquity
( recognized from Middle Ages to 1862;
recognized after 1963.)
Elements that are thought to make up most of the
Earth's core (Fe>Ni>Co), along with possibly S or O
Elements that make natural mineral alloys with Fe
Elements that make natural mineral alloys with Cu
Elements that make natural mineral alloys with Os
Elements that make natural mineral alloys with Pt
Elements that make natural mineral alloys with Au
I 53
r=2.16
(7+ r=0.50)
(124) 127
(128) (130)
Iodine as iodide
m=126.904
–
Bi 83
m=208.980
Bismuth as
2–
bismuthide
The only bismuthide
minerals are of
Pd, Ag, Pt, Au, and Pb
52
m=127.60
120 122 123
r=2.21
128 130
124 125 126
Te
Tellurium
2–
as telluride
Anions that form minerals with Au+
Anions that form minerals with Ag+
Anions that form minerals with K+ and Na+
Anions that form minerals with Al3+, Ti4+, and Zr4+
Anions that form minerals with Si4+
Anions that form minerals with Mg2+
An Earth Scientist's Periodic Table of the Elements and Their Ions
See also Insets 1 to 6.
Inset 7: Conceptual model of the behavior of
oxides of hard (and intermediate) cations
1Å
Li N
Cations
Rb O2–
Low z/r
High z/r
Weak cation-
oxygen bonds
Strong cation-
oxygen bonds
cation-cation
Strong
bonds, but
repulsion
H+
Intermediate
z/r
Si 14
m=28.086
28 29 30
r=0.41
as silicate (SiO4
4–)
4+
or Si(OH)4
0
49 50
Ti 22
m=47.867
46 47 48
r=0.68
Titanic titanium
4+
Ca 20
m=40.078
40 42 43
44 46 48
Calcium ion
2+
r=
0.99
V 23
m=50.942
50 51
r=0.74
vanadium
3+
Vanadous
Cr 24
m=51.996
50 52 53 54
r=0.69
chromium
3+
Chromic
La & 57-
REEs 71
170Yb
See below
3+
3
0
0
0
La 3+
Ba2+
Hf 4+
Ta5+
Cs
+
W6+
Y 3+
Sr 2+
Zr 4+
Nb5+
Rb
+
Mo6+
Sc3+
Ca2+ Ti 4+
V5+
K
+
Cr 6+
Al
Mg2+
Si 4+
P5+
Na
+
S6+
B 3+
Be2+
C4+
N5+
Li
+
Th5+
1700
1193
2681 723 216
3125
1996 855 290
3200
2103 943
F
Fe
2+
-----
Fe
3+
Cr
3+
-----
-----
673 2938 3123 1785 1074
2286 2580
2
5
0
0
3173 2058 1745
3493
2
5
0
0
2
0
0
0
1000
500
3
0
0
0
2
0
0
0
1
5
0
0
1
5
0
0
En
Ti
Ab
Fo
Di
Ksp
An
Q
Il
Cr
Ab
2345
3+
An
Chromite
Forsterite
Anorthite
Augite
Enstatite
Hornblende
Ilmenite
Magnetite
Apatite
Titanite (sphene)
Zircon
Biotite
K-feldspars
Albite
Quartz
Minerals in order of typical
temperature of formation*:
Melting T (K) of simple
oxides of hard cations
Ti 4+
2103
Cation
(outlined for
intermediate
cations)
Melting T (K)
of oxides of
hard cations
Mg-Al-Fe-Ca-
Ti-rich
minerals
Si-Na-K-
rich
minerals
Minerals are shown with size
of circles representing
proportions of cations.
Inset 3: High-temperature behavior of hard cations
Bi
*Order of crystallization in
any one magma depends on
bulk composition, pressure,
and fluid composition.
54 56 57 58
Fe 26
m=55.845
r=0.76
Ferrous iron
2+
8 most abundant solutes dissolved in seawater
9th to 16th most abundant 17th to 22nd most abundant
Ions concentrated in deep-sea ferromanganese nodules
Ions that enter early-forming phases in igneous rocks
Ions that enter later phases in igneous rocks because of
their large size (mostly "large-ion lithophiles")
2nd to 8th most abundant solutes in average river water
Most abundant solute in average river water (HCO3
–)
Ions commonly concentrated in residual soils and residual
sediments. Small symbol ( ) indicates less certainty.
Solutes that can be limiting nutrients in the oceans
Macronutrient solutes on land Micronutrient solutes on land
Ions essential to the nutrition of at least some vertebrates
("essential minerals")
Ions least depleted from mantle in formation of crust
MgAlBO4
(Sinhalite)
NaNO3
(Soda Niter)
Me2+CO3
KNO3
(Nitre)
Na2SO4
(Thenardite)
CaSO4
(Anhydrite)
Al2SiO5 (K-S-A)
ZrSiO4 (Zircon)
KAl2Si3O8 (Kspar)
AlPO4
(Berlinite)
Na3PO4
(Olympite)
(e.g.,
Calcite)
Si 4+
P5+
S6+
B 3+
C4+
N5+
Inset 5: Typical simple oxysalt minerals
(__MOn minerals without OH or H2O)
Minerals with
1+ cations only
Minerals with
1+ to 4+ cations
Minerals
with
1+ & 2+
cations
Minerals
with
1+ to 3+
cations
Periclase
La 3+
Hf 4+
Ta5+
W6+
Y 3+
Sr2+
Zr 4+
Nb5+
Mo6+
Ca2+
Ti 4+
V 5+
K
+
Cr6+
Al
Mg2+
Si 4+
P5+
Na
+
S6+
B 3+
Be2+
C4+
N5+
Li
+
Th5+
3+
9
5.5-6
7.5-8 9 7
3-3.5
5.5
Perovskite
3.5
3-4
7
6
Spinel
Corundum
Bromellite
Lime
Quartz
Shcherbinaite
Molybdite
Tantite
Thorianite
Baddeleyite
6.5
Srilankite
>9
(Ru=6-6.5)
Chrysoberyl
8.5
*A non-rutile synthetic TiO2
is the hardest known oxide
Inset 2: Hardness of oxide minerals of hard cations
7
Quartz
Mineral of
one cation:
5.5
Perovskite
Mineral of
two cations
H
=
4
H
=
4
H
=
6
H
=
8
H
=
6
Hardness
(Mohs
scale)
Periclase
La 3+
Hf 4+
Ta5+
W6+
Y 3+
Sr2+
Zr 4+
Nb5+
Mo6+
Ca2+
Ti 4+
V5+
K
+
Cr6+
Al
Mg
2+
Si 4+
P5+
Na
+
S6+
B 3+
Be2+
C4+
N5+
Li
+
Th5+
3+
Corundum
Lime
Quartz
Shcherbinaite
Molybdite
Tantite
Baddeleyite
Inset 4: Solubility of oxide minerals of hard cations
4.4
Bromellite
–7.4 2.77
9.9
–2.4 –8.1 –3.9 –1.37
14.0
1.4
Sc3+
–9.7 –7.6
Rb
+
28.9
4.3
Ba2+
6.7
Log of activity of cation species
in distilled water at 25 °C
–9.7
Mineral
Thorianite
Rutile
See also Inset 7.
Cr
Mn
2+
Fe
3+
Fe
2+
Co
2+
Ni
2+
Cu+
Zn
2+
Sn
4+
Pb
2+
Bi
3+
2603
2054 1652
1838
2078 2228 1509
2242
1903
1098
1170
Bismite
Massicot
Cassiterite
Bunsenite
Cuprite
Zincite
Hematite
Manga-
nosite
Sb
928
As
547
Cd
2+
>1773
Cu
2+
1719
Tenorite
Ga
3+
2079
Ge
4+
1388
Ag
~473(d)
+
Tl
852
+
Tl
3+
1107
Sn
2+
1353(d)
Hg
2+
773(d)
Montroydite
Valentinite
Au
no stable
oxide
+
2400
2000
1600
1
2
0
0
8
0
0
Inset 6: Melting and decomposition (d) temperatures
(K) of oxides of intermediate and soft cations
Co
3+
1168 (d)
V
4+
2240
Mn
3+
1353(d)
La 3+
Ba2+
Hf 4+
Cs
+
Y 3+
Sr 2+
Zr 4+
Nb5+
Rb
+
Ca2+
Ti 4+
V5+
K
+
Al
Mg2+
Si 4+
P5+
Na
+
B 3+
Be2+
C4+
Li
+
3+
251
Bromellite
Chrysoberyl
240
Periclase
160
254
Corundum
198
Spinel
38
Quartz
210
Perovskite
216
Rutile
115
Lime
87
71
3
145
152*
175
Tausonite
38
Quartz
Mineral of
one cation:
71
Nonmineral:
210
Perovskite
Mineral of
two cations:
200
150
1
0
0
50
Inset 1: Bulk modulus (Ks in GPa)
of oxide minerals of hard cations
*Baddeleyite has
at ambient condi-
Ks = 95 GPa but
stable ZrO2 phase
is for the latter.
is not the most
tions; value shown
F–
Cl–
Br–
I–
Anion:
Na+( )-, and Mg2+( )-bearing halides (mol/L)
HgI2
Villiaumite
Halite
100
1
10-2
10-4
10-6
10-8
Sellaite
Chlorargyrite
Bromargyrite
Iodargyrite
NaBr
NaI
AgF
MgBr2
MgI2
Mineral
Nonmineral
HgBr2
HgCl2
Solubility of Ag+( )-, Hg2+( )-,
of hard and soft cations
Inset 8: Solubility of halides
z / r
=
2
z
/
r
=
1
z
/
r
=
1
z / r
=
4
Cd 48
114 116
111 112 113
r=0.97
106 108 110
m=112.411
Cadmium ion
2+
In 49
m=114.818
1+ r=1.32
113 115
3+ r=0.81
Indium ion
1,3+
Au 79
m=196.967
r=1.37
197
Gold ion
(3+ r=0.85)
+ Tl 81
m=204.383
r=1.40
207 208 210
203 205 206
Thallous thallium
+
Tl 81
r=0.95
Thallic thallium
3+
202 204 206
Hg 80
m=200.59
196 198 199
r=1.19
200 201
Mercurous ion
+
Ag 47
m=107.868
r=1.26
107 109
Silver ion
+
+
63 65
Cu 29
m=63.546
r=0.96
Cuprous copper
Cations that form simple oxide minerals
Cations that form simple sulfide minerals
Cations that form simple fluoride minerals
Cations that form oxysalt minerals
(e.g., S6+ in sulfates, As5+ in arsenates)
Cations that form simple bromide or
iodide minerals
As
5+
588
In
3+
2185
Pd
2+
1023(d)
Rh
3+
1373(d)
Mo
4+
1373(d)
W
4+
~1773(d)
Rh
4+
1173(d)
Pt
2+
598(d)
Au3+
423(d)
Hg+
373(d)
Arsenolite
3+
1600
2000
Avicennite
Ir
3+
1273 (d)
1200
Eskolaite
3+
Wüstite
Tugarinovite
Paramont-
roseite
Argutite
3+
Romarchite
Monteponite
4
0
0
Ti 22
r=0.90
Titanium ion
2+
Mg 12
m=24.305
24 25 26
r=0.65
Magnesium ion
2+
Fe2+
v. 4.6
Ti 22
r=0.75
Titanium ion
3+
Cr 24
r=0.90
chromium
2+
Chromous
H 1
1 2 3
Hydrogen ion
m=1.0079
r=10-5
+
Ni 28
r=0.73
Nickel ion
3+
55
Mn 25
m=54.938
r=0.80
Manganous Mn
2+
59
Co 27
m=58.933
r=0.74
Cobaltous cobalt
2+
61 62 64
Ni 28
m=58.693
58 60
r=0.72
Nickel ion
2+
r=0.69
Cu 29
Cupric copper
2+
Zn 30
m=65.39
64 66
r=0.74
67 68 70
Zinc ion
2+
r=0.62
Ga 31
m=69.723
69 71
(1+ r=1.13)
Gallium ion
3+
70 72
73 74 76
Ge 32
m=72.61
(2+ r=0.93)
r=0.53
Germanium ion
4+
Sc 21
m=44.956
45
r=0.81
(48)
Scandium ion
3+
Al 13
m=26.982
27
r=0.50
3+
Aluminum ion as
Al3+ or Al(OH)n
3–n
Fe3+
because it speciates
both as I– (to right)
Iodine is shown twice
as a solute in seawater
and IO3 (here).
–
H 1
m=1.0079
1 2 3
r=2.08
Hydrogen
–
as hydride
Hg 80
r=1.10
Mercuric ion
2+
*
"K-S-A"
indicates
kyanite,
andalusite,
& sillimanite.
Ge 54
m=72.59
2 3 4
r=1.05
Symbol
Ionic Radius (r) (Å)
Atomic Mass
Most abundant (bold)
Radioactive (italicized)
`-
`+
EC,
_
Naturally
occurring
isotopes
Radioactive
decay pathways
Outline solid for naturally occurring elements or ions;
dashed for ones that rarely or never occur in nature.
Actinium
Element Name
Atomic Number
(number of protons)
(see scale at far right)
z
r
= ionic potential
or charge density
= ionic charge ÷
ionic radius
3+
(or elemental radius
for elemental forms)
z
r = 8
/
z
r =
8
/
z
/r =
4
z
/
r
=
2
6.5
See also Inset 3. See also Inset 6.
(AgCl)
(AgBr)
(AgI)
(MgF2)
(NaF)
(NaCl)
MgCl2
An earth scientist’s periodic table of the elements and their ions
L. Bruce Railsback
Figure 1
Supplement to Geology, v. 31, no. 9 (September 2003)
Figure 1. An Earth Scientist’s Periodic Table of the Elements and Their Ions.
Sources of information used in constructing table and related notes are available in
Appendix DR1 in GSA Data Repository (see text footnote one).

3. 738 GEOLOGY, September 2003
tinides with the hard cations. Th41
thus falls below Hf41
, and U61
falls
below W61
. Trends in the symbols described in the next section extend
across this unconventional but geochemically useful arrangement (Fig.
1).
The table also shows the atomic numbers, atomic masses, natu-
rally occurring isotopes, and naturally occurring decay paths of the
different elements. Names of elements and ionic forms are shown—
e.g., ‘‘Sulfur as sulfate ( )’’ for S61
. Sizes of chemical symbols are
22
SO4
scaled to abundance of the elements in Earth’s crust; seven of the nine
most abundant elements conveniently fall together in one part of the
left side of the new table. Contours of equal ionic potential (charge 4
radius, i.e., z/r) highlighted in blue and brown extend across the table
and parallel trends in natural occurrences, as discussed in the next
section.
PATTERNS AND TRENDS IN THE TABLE
Symbols in the Earth Scientist’s Periodic Table of the Elements
and Their Ions show natural occurrences or enrichments in minerals,
natural waters, soils and sediments, igneous rocks, the mantle, and the
atmosphere, and as critical nutrients (Fig. 1). These symbols fall in
swaths that follow contours of equal ionic potential across the table,
as one would expect from Cartledge (1928a, 1928b), Goldschmidt
(1937), and Mason (1958). As a result, the new table makes apparent
patterns of geochemistry that do not emerge from the conventional
table. For example, many ions with ionic potential between 3 and 10
make oxide minerals, are concentrated in soil and ferromanganese nod-
ules, enter early-forming igneous phases, and are least depleted the
mantle. The result is a red-and-brown swath across the hard and inter-
mediate cations in the new table (Fig. 1). The same swath of hard
cations includes those that make oxides with the highest melting tem-
perature, lowest solubility, greatest hardness, and greatest bulk modu-
lus (insets 1–4 and 6).
On the other hand, hard cations with ionic potential ,4 make
fluoride minerals, include ions abundant in river water and seawater,
and include ions important as nutrients. Cations with ionic potential
.8 likewise include ions abundant in seawater, ions important as nu-
trients, and ions that form oxysalts, such as sulfates and arsenates. The
results are blue-and-green swaths across the new table. Those swaths
extend from the hard cations (which coincide with the lithophile ele-
ments) to the intermediate to soft cations (which coincide as a whole
with the siderophile and chalcophile elements).
Contours of ionic potential continuing from the hard cations to
the intermediate cations (e.g., Mn41
and Fe31
) continue the red-and-
brown swath across the table, in that intermediate cations with ionic
potential of 3–8 also make oxide minerals, are concentrated in soils,
enter early-forming igneous phases, and so on. On the other hand, the
contours for lowest ionic potential (1–2) set off the soft cations, which
include the coinage metals (Cu, Ag, and Au) and form the center of a
region characterized by yellow diamonds that mark ions forming sul-
fide, bromide, and iodide minerals.
The coinage metals and their neighbors are also shown in a section
of the table highlighting elemental forms (the true ‘‘Table of the Ele-
ments’’ within the new table). Symbols and colored fields show that
groups of these elements make alloys. For example, elements alloying
with Os form a small distinct group, and elements alloying with Fe
form a group overlapping little with elements alloying with Cu and
Au.
On the right side of the table, patterns among the anions match
those on the left side. Among the anions of low ionic potential, a blue-
and-green swath of symbols pertaining to solutes mirrors that found in
cations of low ionic potential. From top to bottom is the transition
from anions coordinating with hard cations (resulting in fluorides and
oxides of Na1
, K1
, and Al31
) to those coordinating with soft cations
(resulting in sulfides, bromides, iodides, and tellurides of Ag1
and
Au1
). From right to left, or from Cl2
and F2
to O22
to C42
, is the
transition from anions making minerals with hard cations of low ionic
potential (e.g., K1
and Na1
) to those making minerals with hard cations
of higher ionic potential (e.g., Al31
and Si41
). Minerals exemplifying
this transition are carrobite (KF), sellaite (MgF2), gibbsite (Al2O3),
quartz (SiO2), and moissanite (SiC).
Speciation of hard cations in aqueous solution also follows easily
recognized trends in the new table (bold black lines in Fig. 1). From
lower left to upper right across the hard cations, speciation progresses
from hydration (e.g., K1
) to hydroxo complexes [e.g., and
3–n
Al(OH)n
] to oxo-hydroxo complexes (e.g., COOOH2
and POOOOH2
,
0
Si(OH)4
more familiar as and ) to oxo complexes (e.g., ,
2 22 22
HCO HPO CO
3 4 3
and ) (Stumm and Morgan, 1996; Shock et al., 1997). A
2 22
NO , SO
3 4
trend that is inscrutable in the conventional periodic table thus becomes
readily apparent in the new table. This pattern of coordination, when
extended from solution to solids, places in context the mineralogical
existence of oxysalt minerals such as carbonates, nitrates, and sulfates,
but no ‘‘calciates,’’ or ‘‘sodiates’’, and the existence of aluminate only
as an aqueous species (Pokrovskii and Helgeson, 1997).
Many of these patterns can be explained by consideration of bond
strength and shielding of charge in mineral structures, as is shown
schematically in inset 7. Cations of low ionic potential (e.g., K1
, Na1
,
Sr21
) bond only weakly to O22
, so they do not form oxide minerals
and are not retained in oxide-forming and hydroxide-forming environ-
ments like soils. Instead, they are soluble in aqueous solution, entering
natural waters and crossing cell membranes and root sheaths as nutri-
ents. Their weak bonds to O22
result in their incorporation into igneous
minerals only at relatively low temperatures and thus relatively late in
the crystallization sequence. Cations of intermediate ionic potential
(e.g., Al31
, Ti41
) form relatively strong bonds with O22
, and their tet-
rahedral to cubic coordination allows shielding of the cations’ positive
charges from each other. They thus form stable oxides and hydroxides
in oxidizing environments, and many of them bond in igneous minerals
at high temperatures and thus early in the crystallization sequence.
Their stability as oxides and hydroxides results in low solubility and
low concentration in natural waters and thus leads to their irrelevance
as nutrients. Cations of high ionic potential (e.g., P51
, N51
, S61
) form
very strong bonds with O22
in radicals like , , and , but
32 2 22
PO NO SO
4 3 4
their intense concentration of incompletely shielded positive charge and
resultant repulsion preclude formation of oxides or hydroxide minerals.
Thus, like cations of low ionic potential, they are soluble in aqueous
solution, abundant in natural waters, and cross cell membranes and
root sheaths as nutrients. Their concentration of positive charge causes
them to enter igneous minerals so late that they are among the ‘‘in-
compatible’’ ions in crystallization of silicate magmas.
These considerations help explain the existence, and nonexistence,
of oxysalt minerals (inset 6). Simple silicates (silicates without OH2
and/or H2O) built around Si41
can accommodate 11 to 41 cations.
Simple borates and phosphates, built around cations of higher ionic
potential (B31
and P51
), can only accommodate 11 to 31 cations,
presumably because residual positive charge from borate and phosphate
groups repels 41 cations. Simple carbonates and sulfates, built around
cations of even higher ionic potential, accommodate only 11 and 21
cations. Finally, simple nitrates, built around the tiny highly charged
N51
, only accommodate 11 cations, presumably because the unshield-
ed positive charge from nitrate groups repels any cations of 21 or
greater charge. The same trends, with shifted thresholds, exist in anal-
ogous minerals with OH2
and/or H2O (e.g., hydrous nitrates accom-
modate 11 and 21 but not more highly charged ones, and OH-bearing
sulfates and carbonates accommodate 11 to 31 but not 41 cations).
The result is a predictive model of the existence and nonexistence of
oxysalt minerals of various cations.

4. GEOLOGY, September 2003 739
GENERAL INSIGHTS
Perhaps the most general insight apparent in the new table is that
chemical weathering at Earth’s surface and the evolution of Earth to
separate the mantle and continental crust are geochemically much the
same process: the segregation of hard and intermediate cations of low
and high ionic potential from those of intermediate ionic potential. The
result is (1) concentration of many of the cations of intermediate ionic
potential in the mantle and, at Earth’s surface, in soil (the red-and-
brown swaths in the table) and (2) the ultimate removal of ions of low
and high ionic potential to the oceans (blue swaths in the table). The
process continues in the oceans, in that cations of intermediate ionic
potential are segregated to ferromanganese nodules and have a short
residence time in seawater.
Another major Earth process—life—has followed rules similar to
those dictating mantle evolution and weathering. Because life began
and largely evolved in aqueous solution and because chemical entities
must be dissolved to pass through cell membranes, life has utilized
and depends on soluble chemical forms. The critical nutrients for life
(green symbols in the table) are therefore coincident with the chemical
species dissolved in natural waters (blue symbols in the table). The
evolutionary transition of some life forms to land put them in an en-
vironment in which chemical weathering removes such ions from soils.
The result is a conundrum for water-loving plant life: soils rich in
nutrients are most common in arid regions where those nutrients have
not been removed by weathering, and soils where wet conditions favor
life are typically leached of nutrients. Utilization of 61 ions by both
plants and animals exemplifies this evolutionary challenge: modern
farmers commonly must fertilize plant growth with K1
-bearing fertiliz-
ers, vertebrates frequent salt licks for Na1
, and premodern societies trad-
ed NaCl as a precious substance. Modern humans continue the trend, in
that they consume I2
-supplemented NaCl, drink F2
-supplemented water,
consume K1
-bearing sports drinks, and even take Li1
pills.
SIX EXAMPLES ACROSS THE PERIODIC TABLE
Special Nature of Silicon
In addition to the trends already outlined, many important special
cases in geochemistry become apparent with the new table. For ex-
ample, Si41
is unique in being very abundant (it is the second most
abundant constituent in the crust) and in having an ionic potential at
the boundary between the relatively insoluble cations of intermediate
ionic potential (e.g., Al31
, Ti41
, and Sc31
in the red-and-brown swath
of the table) and cations of high ionic potential that form soluble rad-
icals (e.g., C41
, N51
, P51
, and S61
in the blue-and-green swath). Si41
is thus abundant both in residua from weathering (e.g., in sands and
sandy or kaolinitic soils) and in natural waters, such as river water
(where dissolved silica is the second most abundant dissolved species)
and seawater (where it is the 11th most abundant dissolved species).
The abundance and borderline ionic potential of Si41
also have
important implications in igneous petrology. Most igneous minerals are
silicates, but some of the first phases to form in igneous rocks (e.g.,
spinel and chromite) contain no Si at all, and the first Si-bearing min-
erals to form are forsterite (where Mg is more abundant than Si) and
anorthite (where Ca and Al outnumber Si) (inset 3). Only in later-
forming phases does Si41
become the dominant cation, and only at the
end of Bowen’s reaction series (when incompatible elements enter sol-
ids) does SiO2 form as quartz (inset 3). This paradox of Si41
as a
somewhat incompatible ion in the crystallization of silicate magmas
arises because Si41
is at the upper margin of ionic potentials that allow
formation of stable oxides. In fact, Si41
is just a step away from C41
,
N51
, and P51
, which do not make any such oxide at all because of
their high ionic potential and are ‘‘incompatible’’ in igneous petrology.
The abundance and borderline ionic potential of Si41
also lead to
an interesting feature of plant physiology. Plants take in nutrients like
as solutes, and the borderline ionic potential of Si41
lets it be
2
NO3
taken up as a solute [as H4Si , or more accurately as ]. How-
0 0
O Si(OH)
4 4
ever, Si41
is sufficiently insoluble that some plants build masses of
opaline silica in their tissue (Meunier and Colin, 2001). These mineral
accumulations within plants, called phytoliths, exist because Si41
is
sufficiently abundant and soluble to be taken up through roots in so-
lution but sufficiently insoluble to be maintained as a solid mineral
within wet plant tissue.
Extreme Nature of Gold
If Si has a special role in geochemistry because of its abundance
and location at a threshold in ionic potential, Au is special for opposite
reasons: it is extremely rare, it has an extremely low ionic potential as
Au1
, and Au1
is extremely ‘‘soft’’ in the spectrum from hard to soft
cations. As a result, Au forms no oxide minerals and doesn’t even form
a sulfide of only Au; the only analogues of a hypothetical AuS2 are
two AuTe2 minerals and an Au2Bi mineral. Au’s fondness for large
anions is also seen in its extensive complexing with Cl2
in solution,
to which is attributed much of the transport of gold to generate ore
deposits (e.g., Murphy et al., 2000). On the other hand, the indifference
of Au to oxygen is one of the reasons Au has been so valued by
humans—it continues to shine as an unoxidized metal despite centuries
of exposure to O2. In the conventional periodic table, Au is simply one
of many elements in the middle of that table, but isolation by contours
of ionic potential illustrates its unique nature in the new periodic table.
Applications of Fe, Mn, and Ce as Paleoredox Indicators
The table’s separation of cations and consideration of ionic po-
tential shows why some cations have been used extensively in evalu-
ation of paleoredox conditions. For example, Fe and Mn have been
used in geochemical study of oxidation and reduction (e.g., Hem, 1972)
because they are by far the most abundant elements that form nonhard
cations. They are thus the most abundant elements that can undergo
changes of one in oxidation state (e.g., between 21 and 31 for Fe).
In oxidizing conditions, they are highly charged (5 31) small ions
that are insoluble because of their high ionic potential and resultant
formation of hydroxides. In reducing conditions, they are lesser
charged (21) and larger ions that thus have lower ionic potential and
are soluble. Fe therefore behaves like the soil-forming and oxide-
forming Al31
ion when oxidized to Fe31
, but like the ‘‘weatherable’’
and soluble Mg21
ion when reduced to Fe21
.
Ce is less abundant than Fe and Mn, but otherwise analogous in
that it precipitates in solids when oxidized to Ce41
but is more soluble
as Ce31
. It thus provides an indicator of oxygenation in modern (de
Baar et al., 1988) and ancient (Wright et al., 1987) oceans. Ce31
and
Ce41
also exemplify patterns of coordination seen elsewhere in the
table, in that the ion with lower ionic potential forms a fluoride mineral,
fluocerite-(Ce), whereas the ion with higher ionic potential forms an
oxide mineral, cerianite. The formation of those two minerals parallels
the formation of fluorides by Na1
and K1
but formation of oxides by
Al31
and Sc31
(Fig. 1).
Uranium, Thorium, and Dating Problems
Radiometric dating using the U-series method (Edwards et al.,
1987) is a valuable means of determining the age of materials younger
than ;500 k.y. old. One problem with this method, however, is that
U at Earth’s surface is in the U61
state and thus in the soluble 21
UO2
oxo complex (Langmuir, 1978). Th, on the other hand, occurs as Th41
,
which is insoluble (e.g., Kaufman, 1969). As a result, parent U is
commonly lost from materials but daughter Th remains, giving incor-
rectly old ages (e.g., Dabous and Osmond, 2000). This problem is not
apparent from the conventional periodic table but is predictable in the
new table, where U61
falls in the blue-and-green swath of relatively
soluble hard cations of high ionic potential and Th41
falls in the red-

5. 740 GEOLOGY, September 2003
and-brown swath of relatively insoluble ions of intermediate ionic
potential.
From Silicates to Selenites
As already discussed, Si41
is located at the boundary between
cations of intermediate and high ionic potential in the new table. One
result is that Si41
is one of the few cations that make both an oxide
mineral (quartz) and oxysalt minerals (the many silicates). V51
and
Mo61
are hard cations with about the same ionic potential, and they
also form oxides (shcherbinaite and molybdite) and oxysalt minerals
(the vanadates and molybdates). If one follows the contour for z/r 5
8 from those hard cations to the intermediate and soft cations (Fig. 1),
one arrives at Se41
, which likewise forms an oxide mineral (downeyite)
and oxysalt minerals (the selenites). Like Si41
, V51
, and Mo61
, Se41
is also a cation essential to vertebrate nutrition (McDowell, 1992; Sun-
de, 1997). These similarities illustrate the continuity of trends along
contours of equal ionic potential across the table. The principal differ-
ence in the behavior of Se is that it forms cations with multiple outer-
shell electrons and thus exists as Se61
as well as Se41
. Se61
also forms
oxysalt minerals (the selenates) and is important in nutrition, but, just
as one would expect after following the contour for z/r 5 16 from P51
and S61
in the hard cations (Fig. 1), Se61
does not form an oxide
mineral.
Odd Role of Chloride—Jack of All Trades, Master of None
Cl2
is not as abundant as F2
in the crust, but Cl2
is more abundant
than F2
in most natural waters. The reason for this paradox can be
seen in the new table. Cl2
occupies an intermediate position among
the anions at the right of the table, in that it coordinates with hard
cations to make soluble minerals like sylvite and halite and coordinates
with soft cations to make relatively rare minerals like chlorargyrite
(AgCl) (Fig. 1). By comparison, F2
bonds with hard cations well
enough to make insoluble minerals like fluorite and so is sequestered
in them, leaving relatively low concentrations in natural waters. Cl2
,
in contrast, bonds strongly with neither hard nor soft cations and so
makes only relatively soluble minerals (inset 8). It therefore can reach
high concentrations in natural waters and commonly only precipitates
when it and a weakly bonding cation, Na1
, finally achieve saturation
with respect to halite.
SUMMARY
Organizing the new Earth Scientist’s Periodic Table of the Ele-
ments and Their Ions according to charge yields an arrangement more
conducive to recognizing geochemical trends than that of the conven-
tional periodic table. These trends in mineralogy, aqueous geochem-
istry, igneous petrology, mantle geochemistry, soil and sediment chem-
istry, and nutrient chemistry are largely controlled by coordination of
cations with O22
. This synthesis of geochemistry from mantle to soil
to seawater provides a framework for understanding Earth systems and
predicting geochemical relationships that is not recognizable with con-
ventional, elementally constructed, periodic tables.
ACKNOWLEDGMENTS
I thank my colleagues at the University of Georgia for their helpful com-
ments and especially Michael F. Roden for his insights about igneous processes.
The manuscript was improved by the comments of two anonymous Geology
reviewers and editor Ben van der Pluijm. Publication was supported by National
Science Foundation grant DUE 02-03115.
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Manuscript received 27 January 2003
Revised manuscript received 2 May 2003
Manuscript accepted 6 May 2003
Printed in USA