Geochemistry involves studying the chemical composition of Earth and other planets, as well as the chemical processes that govern rocks, water, and soils. It examines how chemical elements are distributed and move through different parts of Earth over time. Key techniques for geochemical analysis include electron probe microanalysis and X-ray fluorescence spectrometry. Proper interpretation of geochemical data requires considering analytical uncertainty and discussing limitations with laboratory experts.

1. Geo-Chemistry

2. Introduction to Geochemistry
The field of geochemistry involves:
1.The Study of the chemical composition of the Earth and other
planets.
2.The Chemical processes and reactions that govern the
composition of rocks, water, and soils.
3.The cycles of matter and energy that transport the Earth's
chemical components in time and space, and their interaction
with the hydrosphere and the atmosphere.

3. Introduction to Geochemistry
Some subsets of geochemistry are:
a)Isotope geochemistry: Determination of the relative and absolute
concentrations of the elements and their isotopes in the earth and on earth's
surface.
b)Examination of the distribution and movements of elements in different parts of
the earth (crust, mantle, hydrosphere etc.) and in minerals with the goal to
determine the underlying system of distribution and movement.
c)Cosmo chemistry: Analysis of the distribution of elements and their isotopes in
the cosmos.
d)Biogeochemistry: Field of study focusing on the effect of life on the chemistry
of the earth.
e)Organic geochemistry: A study of the role of processes and compounds that
are derived from living or once-living organisms.
f)Water Geochemistry: Understanding the role of various elements in
watersheds.
g)Regional, environmental and exploration geochemistry: Applications to
environmental, hydrological and mineral exploration studies.

4. The main focus of geochemistry is to:
 Understand the principles governing the distribution and re-
distribution of elements, ionic species and isotope ratios in
earth materials, so that we can interpret the formation of
mineral assemblages: conditions (P, T, etc.), processes
(magmatic crystallization, weathering, chemical precipitation,
metamorphism, etc.), and even the age.
 Predict changes in mineral assemblages (minerals,
concentrations of elements, isotopic ratios) if a given mineral
assemblage is subjected to different conditions (T, P,
interaction with a fluid, etc.)
 Geochemistry plays an important role in forecasting the
quality of crude oil in the accumulation.
Geochemistry = chemistry of the Earth
(i.e., of earth materials — minerals and rocks)

5. THE EARTH'S CHEMISTRY
The bulk of the Earth is made from iron, oxygen, magnesium and silicon.
More than 80 chemical elements occur naturally in the Earth and its atmosphere.
Mostly Earth is composed of three parts:
1. Crust
2. Mantle (Upper & Lower)
3. Core
The Earth's crust is a thin layer of rock that floats on the mantle. The crust is made mostly
from oxygen and silicon (silicate minerals such as quartz), with aluminium, iron, calcium,
magnesium, sodium, potassium, titanium and traces of 64 other elements.
The upper mantle is made up of iron and magnesium silicates; the lower is silicon and
magnesium sulphides and oxides.
The core is mostly iron, with little nickel and traces of sulphur, carbon, oxygen and
potassium.

7. Fig.- This diagram shows the percentages of the chemical elements that make up the Earth.
Fig.- This diagram shows the Earth interior.

8. EARTH'S INTERIOR
The Earth's crust is a thin hard outer shell of rock. Under the crust, there is a deep
layer of hot soft rock called the mantle.
The crust and upper mantle can be divided into three layers according to their
rigidity:
1.The lithosphere (The lithosphere is the upper, rigid layer of the
Earth. It consists of the crust and the top of the mantle and it is about
100 km thick).
2.The asthenosphere (Below the lithosphere, in the Earth's mantle, is
the hot, soft rock of the asthenosphere. The boundary between the
lithosphere and the asthenosphere occurs at the point where
temperatures climb above 1300°C).
3. The mesosphere. the solid part of the earth's mantle lying
between the asthenosphere and the core.

9. EARTH'S INTERIOR
Beneath the mantle is a core of hot iron and nickel.
The outer core is so hot (4500°C - 6000°C) that it is
always molten. The inner core is even hotter (up to
7000°C) but it stays solid because the pressure is 6000
times greater than on the surface.
The inner core contains 1.7% of the Earth's mass, the
outer core 30.8%; the core - mantle boundary 3%; the
lower mantle 49%; the upper mantle 15%; the ocean
crust 0.099% and the continental crust 0.374%.

10. Fig.- The main layers that form the Earth.
 Our knowledge of the Earth's interior comes mainly from studying how earthquake
waves move through different kinds of rock.
 Analysis of how earthquake waves are deflected reveals where different materials
occur in the interior. S (secondary) waves pass only through the mantle. P (primary)
waves pass through the core as well. P waves passing through the core are deflected,
leaving a shadow zone where no waves reach the far side of the earth.
 The speed of earthquake waves reveals how dense the rocky materials are. Cold, hard
rock transmits waves more quickly than hot, soft rock.

11. Geo Chemical Classification of Elements
 There are several trials to classify elements on geochemical basis.
 Names such as siderophile, chalcophile, lithophile, hydrophile,
thalassophile, atmophile are commonly used to denote the particular
geochemical affinity of elements.
 chemical affinity is the electronic property by which dissimilar chemical
species are capable of forming chemical compounds or Affinity is the
tendency of a molecule to associate with another.
.
 Chemical affinity can also refer to the tendency of an atom or compound to
combine by chemical reaction with atoms or compounds of unlike
composition.

12. Geochemical Affinity
In the classification scheme of Goldschmidt, elements are divided
according to how they partition between coexisting silicate liquid, sulfide
liquid, metallic liquid, and gas phase…
Silicate Liquid
Sulfide Liquid
Metallic Liquid
Gas PhaseGas Phase
Siderophile
Chalcophile
Lithophile
Atmophile H, He, N, Noble gases
Alkalis, Alkaline Earths,
Halogens, B, O, Al, Si, Sc,
Ti, V, Cr, Mn, Y, Zr, Nb,
Lanthanides, Hf, Ta, Th,
U
Cu, Zn, Ga, Ag, Cd, In, Hg,
Tl, As, S, Sb, Se, Pb, Bi,
Te
Fe, Co, Ni, Ru, Rh, Pd, Os,
Ir, Pt, Mo, Re, Au, C, P, Ge,
Sn
Melting a chondrite gives 3 immiscible liquids plus vapor:

13. H
Li
Na
K
Rb
Cs
Fr
Be
Mg
Ca
Sr
Ba
Ra
Sc
Y
Ti
Zr
Hf
Rf
V
Nb
Ta
Db
Cr
Mo
W
Sg
Mn
Tc
Re
Bh
Fe
Ru
Os
Hs
Co
Rh
Ir
Mt
Ni
Pd
Pt
Cu
Ag
Au
Zn
Cd
Hg
Ga
In
Tl
Ge
Sn
Pb
As
Sb
Bi
Se
Te
Po
Br
I
At
Kr
Xe
Rn
B
Al
C
Si
N
P
O
S
F
Cl
Ne
Ar
He
La
Ac
Ce
Th
Pr
Pa
Nd
U
Pm
Np
Sm
Pu
Eu
Am
Gd
Cm
Tb
Bk
Dy
Cf
Ho
Es
Er
Fm
Tm
Md
Yb
No
Lu
Lr
1
2
3
4
5
6
7
IA IIA IIIA IVA VA VIA VIIA VIIIA
IIIB IVB VB VIB VIIB VIIIB IB IIB
Lanthanides
Actinides
1
3
11
19
37
55
87
4
12
20
38
56
88
21
39
22
40
72
104
23
41
73
105
24
42
74
106
25
43
75
107
26
44
76
108
27
45
77
109
28
46
78
29
47
79
30
48
80
5
13
31
49
81
6
14
32
50
82
7
15
33
51
83
8
16
34
52
84
9
17
35
53
85
10
18
36
54
86
2
57
89
58
90
59
91
60
92
61
93
62
94
63
95
64
96
65
97
66
98
67
99
68
100
69
101
70
102
71
103
Atmophile
Lithophile
Chalcophile
Siderophile
Artificial
What makes an element siderophile or lithophile?What makes an element siderophile or lithophile?
Notably, the Goldschmidt categories are well-Notably, the Goldschmidt categories are well-
grouped in thegrouped in the periodic table of the elementsperiodic table of the elements::

14. Lithophile elements:
Lithophile elements mainly consist of the highly reactive metals of the s-and f-blocks.
They also include a small number of reactive nonmetals, and the more reactive metals
of the d-block such as titanium, zirconium and vanadium.
Siderophile elements:
Siderophile elements are the high-density transition metals that tend to bond with
metallic iron in the solid or molten state.
Chalcophile elements:
Chalcophile elements are those metals (sometimes called "poor metals") and heavier
nonmetals that have a low affinity for oxygen and prefer to bond with sulfur as highly
insoluble sulfides.
Atmophile elements:
Atmophile elements are defined as those that are found chiefly or exclusively in the
form of gases.

15. Ionization potential 
Energy required to remove the least tightly bound electron.
Electron affinity 
Energy given up as an electron is added to an element.
Electronegativity 
Quantifies the tendency of an element to attract a shared
electron when bonded to another element.
Properties derived from outer electrons

16. Electronegativity of elements

17. Chemical Weathering

18. Chemical Weathering
Weathering is a process of the disintegration and degeneration of rocks
minerals or soils as a result of direct contact with the atmosphere of the Earth
OR The disintegration, or breakdown of rock material is called Weathering.
Three types of weathering:
1)Chemical weathering: breakdown as a result of chemical reactions (CaCO3+CO2+H2O
---> Ca2+
+ 2HCO3-
)
2) Mechanical Weathering: No change in chemical composition, just disintegration into
smaller pieces
3) Biological Weathering: Can be both chemical and mechanical in nature
(For Example: Tree throw).
The rate of weathering differs with variation in the chemical composition
and structure.

19. Chemical Weathering
Definition: Transformation/decomposition of one mineral into another
Mineral breakdown
• carbonate dissolves
• primary minerals --> secondary minerals (mostly clays)
 Water is the main operator:
 Dissolution
Many ionic and organic compounds dissolve in water
Silica, K, Na, Mg, Ca, Cl, CO3, SO4
water + carbon dioxide + calcite dissolve into calcium ion and bicarbonate ion
H2O + CO2 + CaCO3 --> Ca+2
+ 2HCO3
-
 Acid Reactions
Water + carbon dioxide <---> carbonic acid
Water + sulfur <--> sulfuric acid
H+
effective at breaking down minerals

20. Chemical Weathering
 Oxidation
Oxygen dissolved in water promotes oxidation of sulfides, ferrous
oxides, native metals
 Organic Activity
Plant material makes H+
ions available
Hydration
Attachment of water molecules to crystalline structure of a rock, causing
expansion and weakness
Hydrolysis
combination of hydrogen and oxygen in water with rock to form new
substances

21. Factors that Influence Chemical Weathering
The factors that influence Chemical weathering are,
 The climate of the place
(Temperature and moisture characteristics).
The vegetation
(Most effective in areas of warm, moist climates – decaying vegetation creates
acids that enhance weathering)
The physical nature of the rock.
In case of Chemical weathering water plays a major role as is
evident from the description of methods, therefore in the absence of
water, chemical weathering is nearly impossible.

22. TYPES OF WEATHERING REACTIONS

23. Geochemical analysis
 Geochemistry is the study of the composition of geological materials and
the behavior of individual elements during geological processes.
 Geochemical analysis is now a vital tool in most fields of geological and
environmental research.
 It is used, for example, in studies of water, soil, and air quality, of
formation of rocks and minerals, of fossilization mechanisms, of metal
accumulation in organisms from contaminated water and soil.
 Some of the most commonly available geochemical techniques are
described below.
 Electron probe microanalysis (EPMA)
 X-ray fluorescence spectrometry (XRF)

24. Electron probe microanalysis (EPMA)
 EPMA is a non-destructive technique for the analysis of polished
and carbon-coated specimens of minerals, glasses, and synthetic
materials.
 It can also be used to give an indication of the elements present
in organic or unpolished or uncoated materials. Analyses can be
made at individual points (usually 1 to 40 m (micrometres) inμ
diameter) or over small areas (usually less than 1 mm2
) of the
sample surface to produce geochemical maps.
 Specimens are introduced into the sample vacuum chamber and
viewed under high magnification to select areas of interest. A
beam of electrons is fired at the surface of the sample, producing
X-rays with energies and wavelengths specific to the elements
present.

25. Electron probe microanalysis (EPMA)
 The instrument is calibrated by analyzing standard samples with known
compositions.
 Among the most useful applications of EPMA is in the study of subtle
chemical zoning in minerals by element mapping. Zoning of this kind, which is
often invisible using light microscopy, can yield information on crystallization
conditions and changes in the chemistry of a magma or hydrothermal fluid.

26. X-ray fluorescence spectrometry (XRF)
 XRF is a routine technique for the determination of major elements and
many trace elements in rocks and minerals, at concentrations from 1 or 2
ppm (parts per million) to 100 per cent.
 Samples are usually prepared as glass discs for major element analyses, by
fusing the sample powder with a known proportion of a commercially
available flux, or as pressed powder pellets for trace-element analyses,
made by mixing the sample powder with a binding agent, then pressing
the mixture into a compact disc with a smooth upper surface.
 The sample surface is irradiated with primary X-rays, producing
secondary X-rays with energies and wavelengths characteristic of the
elements present.

27. X-ray fluorescence spectrometry (XRF)
The concentration of the elements is determined by comparing the intensity of
the various energy or wavelength peaks with those produced by standard
samples of known composition.
One of the most common uses of XRF is in the geochemical analysis of suites
of igneous, metamorphic, and sedimentary rocks in studies of crustal and
mantle evolution.

28. The interpretation of geochemical data
 Data for major elements are generally reported in the form of
oxides as weight per cent (e.g. silica, SiO2 wt. percent) and trace
elements in parts per million (ppm) or micrograms per gram ( gμ
g 1−
).
 An important consideration in the interpretation of data is
analytical uncertainty, particularly when evaluating the existence
or significance of small variations in composition.
 Some of the most common sources of uncertainty are sample
contamination, incomplete sample digestion (some minerals are
extremely resistant to acids), interferences between elements (for
example in EPMA, where X-ray energies for two elements may
overlap), and poor instrument calibration.

29. The interpretation of geochemical data
 The extent of these problems is best limited at the time of analysis by taking
necessary precautions and through discussion with experienced laboratory staff.
 They are, however, impossible to eliminate completely and an indication of
analytical uncertainty should therefore be reported with the data, ideally as
‘error bars’ on geochemical diagrams.
 Uncertainties can be estimated from the regular analysis of reference materials
of known composition and from the analysis of two or more samples.
 To help in interpretation, data are often imported into graphing and statistical
computer programmes.
 A wide variety of diagrams can be produced to compare the data with those
from previous studies and to demonstrate trends or new interpretations.