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PRINCIPLES OF GEOCHEMISTRY
An Introduction
M. Mahfudz Fauzi S., S.Pd., M.Sc.
STUDY PROGRAM OF CHEMICAL EDUCATION
DEPARTMENT OF MATHEMATIC AND NATURAL SCIENCE
FACULTY OF TEACHER TRAINING AND PEDAGOGY
UNIVERSITY OF LAMPUNG
The Subject of Geochemistry
• Geochemistry : The chemistry of earth materials. It
deals with the distribution and the migration of
chemical elements within the earth.
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A ROCKY CRUST layer ~ 100 km thick.
A MANTLE layer, denser
than the crust layer, and
"plastic" meaning that it
can flow. Extends to ~
2900 km below the surface
AN OUTER CORE
layer that is a liquid
iron/nickel mixture.
AN INNER CORE
layer that is a solid
iron/nickel mixture.
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The Subject of Geochemistry
• Cosmochemistry : The science of the occurrence
and the distribution chemical elements in the whole
universe.
• In order to understand the chemistry of the earth, it
is important that we know about the chemistry and
the history of the sun, and the other planetary
bodies in the solar system as well as the chemistry
of the stars and interplanetary and interstellar space.
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The Purpose of Geochemistry
Based on Goldschmidt opinion:
1. To determine quantitatively the composition of the
earth and its parts; and
2. To discover the laws (theoretical descriptions)
which control the distribution of the individual
elements
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In order to solve the problems :
• Geochemist requires a comprehensive collection of
analytical data on terrestrial materials, such as
rocks, waters, and atmosphere.
• Geochemist also uses analyses data of meteorites,
astrophysical data on the composition of other
cosmic materials, and geophysical data on the
nature of the earth’s interiors
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The Tasks of Geochemistry
Based on Mason opinion:
1. The determination of the relative and absolute
abundances of elements and the atomic species
(isotopes) in the earth.
2. The study of distribution and migration of the
individual elements in the various parts of the earth
(the atmosphere, hydrosphere, crust, etc.), and in
minerals and rocks, with the objective of discovering
principles governing the distribution and migration.
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A Brief History of Geochemistry
• The name “geochemistry” was first introduced by
Schonbein since more than 150 years.
• Clark, who was a chief chemist of the US. Geological
Survey from 1884 to 1925, has contributed very much to
the science "geochemistry".
• The modern science of geochemistry can be dated back
to Clark who published a very large number of chemical
analyses of the various rocks in the earth's crust. He
computed averages for each common rock type and
studied the mutual abundance and distribution of many
major and minor elements.
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• Goldschmidt (1888-1947) contributed significantly to
the roles of ionic size, coordination, and atomic
substitution in crystal lattices.
• He gave a practical definition for the science
geochemistry, as it deals with:
a. the abundance of elements in rock, mineral or
crystal,
b. the distribution of the elements, and
c. laws governing the abundance and distribution of
elements in rock, mineral or crystal.
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The Discovery of Elements
ERA
Alchemy
Lavoisier
1789
ELEMENTS
: Au, Ag, Cu, Fe, Pb, Sn, Hg, S, and C.
O, N, H, P, Cl, F, B, Sb, As, Bi, Co, Mn, Mo,
Ni, Pt, W, Zn, Ca, Mg, Ba, Al, and Si.
1800 - 1809
: Na, K, Nb, Rh, Pd, Ce, Ta, Os, and Ir.
1810 - 1819
: Li, Se, Cd, and I.
1820 - 1829
: Br, and Th.
1830 - 1839
: V, and La.
1840 - 1849
: Ru, Tb, and Er.
1850 - 1859
: -
1860 - 1869
: Rb, In, Cs, and Tl
1870 - 1879
: Sc, Ga, Sm, Ho, Tm, and Yb.
1880 - 1889
: Ge, Pr, Nd, Gd, and Dy.
1890 - 1899
: He, Ne, Ar, Kr, Xe, Po, Ra, and Ac.
9
22
43
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The processes by which the Earth formed led to its
differentiation into different layers.
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Elemental Abudance
• The abundance of an element is the amount of that
element in a particular region of the natural world.
• Elements are not equally abundant in all regions –
abundances differ due to the differences in physical
and chemical behavior of the elements.
• The core of the Earth is rich in dense Group 8 to 10
metals.
• The Earth’s crust has the largest share of
nonmetals, metalloids, and light active metals.
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Cosmic and Terrestrial Abundances
(Mass %) of Selected Elements.
Compositional Phases of the Earth
• As the Earth cooled to form its major layers, gravity and
convection caused materials of different densities to
separate, giving several phases.
• Fe was the major component of the core or iron phase.
• The outer silicate phase, containing oxygen combined
with Si, Al, Mg, and some Fe, separated into the mantle
and crust.
• The sulfide phase, with intermediate density, consisted
mostly of iron sulfide mixed with parts of the other
phases.
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Geochemical Differentiation of The
Elements.
Distribution of the Elements
 The distribution of the elements in the Earth’s layers was
controlled by their chemical affinity for one of the three
phases.
 Elements with low or high electronegativity tended to
congregate in the silicate phase as ionic compounds.
These included active metals and nonmetals.
 Metals with intermediate EN dissolved in the iron phase.
 Lower-melting transition metals, and many metals and
metalloids in Groups 11 to 16, became concentrated in
the sulfide phase.
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Impact of Life on Crustal
Abundances
 Photosynthesis resulted in an increase in the O2 levels of the
atmosphere.
 Oxidation became the major source of free energy in the crust and
biosphere.
 The [K+] of the oceans is much lower than the [Na+]
 since growing plants have absorbed dissolved K+.
 Subterranean deposits of organic carbon formed from the
decomposition of ancient plants under high pressure.
 Fossilized skeletal remains of early marine organisms have
formed vast deposits of C, O and Ca.
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Ancient Effect of An O2-Rich
Atmosphere.
Banded-iron formations
containing Fe2O3
Fossil of early multicellular
organism
Abundances of Selected Elements in the
Crust, Its Regions, and the Human Body as
Representative of the Biosphere (Mass %)
Sources of the Elements
 O2, N2, and the noble gases (except He) are
obtained from the atmosphere, where they occur as
the free elements.
 A few elements occur naturally in their uncombined
(native) state. These include S, carbon in coal, and
unreactive metals.
 Most elements occur in ores, natural compounds or
mixtures from which an element must be extracted.
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Environmental Cycles
 An environmental cycle is a natural process in
which elements are continuously cycled in
various forms between different regions of the
Earth’s crust.
 Elements are cycled through physical,
biological, and chemical pathways via
biogeochemistry process.
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exogenic
cycle
endogenic
cycle
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 The most important of these cycles from
the perspective of living organisms are
the carbon, nitrogen, and phosphorus
cycles.
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Earth is Dynamic Planet
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