Geochemistry

Geochemistry

It is the study of the nature and distribution of chemical elements in rock and minerals, and the application of chemistry to earth sciences

Victor M. Goldschmidt

Father of modern chemistry and crystal chemistry, who proposed the classification

Nucleosynthesis

the theory that explains the complexation of material from the simple structure of H and deuterium (isotope of H), or simply the creation of new atoms from hydrogen

Lithophile

rock-loving

Siderophile

Iron-loving

Chalcophile

ore-loving

Atmophile

Gas-loving

Oddo-Harkins Rule

The rule where there is a regular pattern in elements where elements with even atomic numbers are more abundant on either side than those with odd atomic numbers

H, He, C, N, O, Ne, Mg, Si, S, Fe; H and He

10 elements which have atomic numbers of less than 27 showing appreciable abundance with ____ having the greatest abundance

stable minerals

possess the lowest potential energy possible for a mineral

unstable minerals

possess the highest potential energy possible for a mineral

iron, stoney, stoney-iron

three types of meteorite

metastable minerals

They require an energy boost to put in the most stable form of lower potential energy

Stability fields

areas representing the range of applied pressure and temperature in which a mineral may exist in its stable form

Phase boundary

The line separating various stability fields and defines a restricted set of circumstance under which the separated phase coexist in equilibrium

Activation energy

energy required for transformation to take place and is represented by the height of the energy hurdle

Thermodynamics

A branch of chemistry concerned on the free energy changes associated with chemical equilibrium between phases, and provides the tools for working out which mineral assemblages will be stable under which conditions

Chemical kinetics

A branch of chemistry that deals with the mechanics of the reactions that lead to equilibrium, and the rates at which they occur

Phase

a part of parts of a system occupying a specific volume and having uniform physical and chemical characteristics which distinguishes it from all other parts of the system

Component

It comprises the minimum number of chemical, both atomic and molecular, species required to specify completely the compositions of all the phases present.

Thermal equilibrium

A state of equilibrium where the distribution where all parts of the system have the same temperature and no net transfer of heat

Chemical equilibrium

a state of equilibrium where the distribution of components among the phases of a system has become constant, showing no net change with time

Equilibrium

The state where for every element present the flux of atoms across the crystal boundary is the same in both directions resulting in zero net flow, and no change of composition in time

Disequilibrium

The state where the diffusion rates of an element in and out of the crystal are unequal, where there will be a net change of composition of each phase with time.

Gibbs Phase Rule

A formula which expresses the number of phases that can coexist in mutual equilibrium in terms of the number of components in the system and another property of the equilibrium called the variance which is also known as the number of degrees of freedom

Invariant

A state of equilibrium with 0 degrees of freedom, implying that the phase equilibrium assemblage completely constrains the state of the system to a particular combination of P and T.

Univariant

A state of equilibrium with 1 degree of freedom, indicating that the state of the system is only constrained in one direction which is along the phase boundary

Divariant

A state of equilibrium with 2 degrees of freedom, showing that the pressure and the temperature can vary independently without upsetting the equilibrium phase assemblage

Solidus

The boundary in the phase diagram where minerals start to melt or becomes completely solid, depending on the direction of movement of the point

Liquidus

The boundary in the phase diagram where minerals start to crystallize or becomes completely liquid, depending on the direction of movement of the point

Eutectic point

An invariant point in the phase diagram where the maximum number of allowable phases intersect and are in equilibrium; where the liquidus and solidus intersect

Peritectic point

An invariant point in the phase diagram where two phases that could never co-exist together react with each other to produce a new phase

Congruent melting

It is the melting that produces a liquid with the same composition as the solid

Incongruent melting

It is the melting that produces a liquid with different composition from the original solid, which then produces a solid with a different composition from the original material

Solvus

A boundary on the phase diagram between the solidus and subsolvus, or a two-phase and one-phase regions

Subsolvus

A state in a phase system where the solvus is truncated, and no mid-range phase can form above it

Hypersolvus

A phase above the solvus where there is a single solid phase that is followed by solid-state exsolution

Lever rule

A formula used in phase diagrams to determine the amount of phases at a point

Compatible elements

Ions that are easily accommodated in the crystal lattice and mineral structure

Incompatible elements

ions that do not fit into the mineral structure of rock-forming minerals at the time of crystallization

Sc, La, Ce, Pr, Nd, Pm, Sm, Eu

Light Rare Earth Elements

Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu

Heavy Rare Earth Elements

Harker Diagrams

Bivariate diagrams showing the relative content relationship of oxide compounds FeO, MgO, CaO, Na2O, K2O, and TiO2 with SiO2 as the magma evolves, creating a trend in the diagram

Ru, Rh, Pd, Re, Os, Ir, Pd

Siderophiles are mostly used to study melting and crystallization in mafic-ultramafic systems in which PGEs are typically hosted by sulfides.

Sc

Indicates pyroxene fractionation as it is concentrated in pyroxenes

Sr

A compatible element in low P but incompatible in high P, and may substitute for Ca in plagioclases and K in potassium feldspars

REE

indicates source characteristics and liquid evolution, with HREEs being more accommodated by Garnet, and sometimes by opx and hornblende, compared to LREEs

Y

commonly incompatible and strongly partitioned into garnet and amphibole

X-ray Fluorescence

A non-destructive, analytical technique that determines the elements present in the composition of a material by measuring the fluorescent, or secondary X-ray emitted by a sample when it is agitated by a primary x-ray source; ore grade determination, petrological studies

X-ray Diffraction

A non-destructive tool for quantifying present compounds in minerals, rocks, soils and particulates by detecting the signature x-ray diffraction pattern of the compounds present within the material; clay mineralogy studies

Atomic Absorption Spectroscopy (AAS)

A spectroanalytical technique used for quantitative determination of elements present in a material by using their absorption of optical radiation (light) by free atoms in the gaseous state; trace element analysis, quantitative analysis of metals

Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

An analytical technique for determining elements present in a material by quantifying the number of ions at a certain mass of the element; isotope analysis of elements

Peritectic point

An invariant point in the phase diagram where two phases that could never co-exist together react with each other to produce a new phase

Congruent melting