Geology Unit 5: Crystallization of Magma

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Questions and Answers

What is the maximum number of degrees of freedom for a one-component system according to the phase rule?

2 (correct)

Which of the following correctly identifies the phases present in the H2O system?

Only gaseous

Solid, liquid, and gaseous (correct)

Solid and liquid only

Liquid and gaseous only

What term describes a curve where two phases coexist in equilibrium in a phase diagram?

Metastable curve

Vapor pressure curve

Stable curve

Phase boundary (correct)

At what temperature does the vapor pressure of water equal atmospheric pressure?

100 ºC Signup and view all the answers

How does increasing temperature generally affect the stability of the liquid phase in a one-component system?

It increases stability up to a point. Signup and view all the answers

Which statement is true regarding the unicomponent system phase diagram?

It includes curves representing multiple equilibria. Signup and view all the answers

What is a key characteristic of the solid phase in the H2O system at low temperatures?

It forms ice which is a stable phase. Signup and view all the answers

In the context of the one-component phase diagram, what does the term 'bivariant' imply?

The system requires two variables to define its state. Signup and view all the answers

What occurs at the low-quartz/high-quartz phase boundary?

High quartz is converted into low quartz. Signup and view all the answers

Which minerals are associated with high-pressure varieties of SiO2?

Stishovite and coesite Signup and view all the answers

In a bicomponent system, what represents the crystallization of two end members?

Eutectic crystallization Signup and view all the answers

Which statement best describes a solid solution in a bicomponent system?

Minerals with similar lattice structures mix easily. Signup and view all the answers

How do temperature and pressure affect the phase of SiO2?

Decompression leads to conversion to other polymorphs. Signup and view all the answers

What is the primary type of reaction represented by ‘Liquid+Solid1=Solid2’?

Peritectic reaction Signup and view all the answers

What is a characteristic of immiscible components in a binary system?

They can form a crystal of intermediate composition only by reaction. Signup and view all the answers

What type of phase relation describes the melting points in a binary eutectic system?

Solidus and liquidus lines Signup and view all the answers

What is the term for the point at which two liquidus lines converge in a phase diagram?

Eutectic point Signup and view all the answers

In a binary eutectic system, what indicates the range of conditions over which the system can exist in equilibrium?

Phase Diagram Signup and view all the answers

Which equation accurately expresses the Phase Rule for determining the degrees of freedom in a system?

F = C - P + 2 Signup and view all the answers

What is the role of the lever's rule in a binary eutectic system?

To define component proportions Signup and view all the answers

What characterizes a homogeneous crystal formed from two mineral components?

They are isomorphous and miscible in all proportions. Signup and view all the answers

What happens to the ratio of solid to liquid phases as the time progresses in a binary eutectic system?

It increases over time. Signup and view all the answers

How many intensive parameters are typically involved in the expression of the Phase Rule?

Two Signup and view all the answers

In the context of chemical systems, what defines a component?

The minimum number of independent chemical species required to define the system Signup and view all the answers

Study Notes

Unit 5: Crystallization of Magma

Magma is a complex mixture of solids, fluids, and dissolved gases, primarily silicate melts with water and other volatiles.
Minerals in igneous rocks crystallize at various temperatures, following a sequence described in the Bowen reaction series.
This unit explores unicomponent and bicomponent (binary) systems, the application of the phase rule, and equilibrium crystallization.

5.1 Introduction

Magma consists of complex mixtures of solids, fluids, and dissolved gases.
Magma is hot silicate melts with significant amounts of water and other reactive fluids/gases.
Volatiles in magma lower its viscosity.
Minerals crystallize in a specific order from magma, as explained by the Bowen reaction series.
This unit delves into the study of unicomponent and binary systems, phase rule, and equilibrium crystallization.

5.2 Phase Rule

System: A portion of the universe isolated for study (open, closed, or isolated).
Phase: A physically distinct part of a system with uniform chemical and physical properties (e.g., liquid, solid, gas).
Component: The smallest number of chemical constituents to define all phases within the system.
Variance (f): The minimum number of variables (like pressure, temperature, and composition) needed to completely define the state of a system at equilibrium.
The phase rule helps understand and study more complex systems.
It explains how many variables need to be controlled to determine a specific state.

5.3 Unicomponent System

A system with only one component (e.g., H₂O or SiO₂).
The behavior of a system with a single component is simpler to analyze than more complex systems.
Phase diagrams: Graphical representations of the conditions (pressure and temperature) under which phases exist and transform into one another.
Phase diagram for H₂O: Shows a solid (ice), liquid (water), and gas (water vapor) phases.
- Phase boundaries: Separate the fields corresponding to the different phases.
Phase diagram for SiO₂: Represents various silica polymorphs (e.g., quartz, cristobalite, tridymite). The diagram demonstrates conditions under which these various phases exist.

5.4 Binary System

A system with two components (e.g., albite-anorthite).
Solid solution: Minerals with similar structures form solid solutions of indefinite proportions. The components mix completely, having variable composition.
Mixed crystals: Homogeneous crystals formed by the mixing of two or more components.
Miscible components: Form solid solutions in any proportion.
Immiscible components: Do not mix in solid state and their compositions are distinct.
Binary system with complete solid solution: Example—Ab-An system (albite and anorthite).
The components show mutual solubility and form a solid solution series.

5.5 Lever Rule

Geometrically determining the relative amounts of phases in a binary mixture.
The lengths of tie lines in a phase diagram can calculate the abundance of each phase.

5.6 Binary Eutectic System

Eutectic point: The fixed temperature at which two minerals crystallize or melt simultaneously.
If mineral mixtures are heated at a fixed pressure, one resulting liquid solution with fixed composition is formed. The temperature at which these two minerals melts is called eutectic melting temperature.
The lever rule can be used to calculate the relative proportions of components during this process.

5.7 Summary

The phase rule governs the simultaneous existence of phases in a system.
A component is the minimum number needed to define all phases in a system; the number of components depend on composition and the range of conditions under which it is studied.
Phase diagrams show relationships between phases in a system, including conditions of pressure and temperature.
The phase rule for condensed systems is adjusted according to the pressure or temperature holding constant in a different system.
Diagrams are used to analyze the behavior of a melt in a particular composition.

5.8 Activity

Redraw and discuss the phase diagrams for water and an albite-anorthite system.

5.9 Terminal Questions

Questions on phase diagrams, phase rule, crystallization behaviour of SiO₂, binary systems, and the lever rule.

5.10 References

A list of recommended reading materials.

5.11 Further/Suggested Readings

A list of further resources.

5.12 Answers

Answers to self-assessment questions.

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Description

This quiz focuses on the crystallization of magma, exploring the complexities of magmatic mixtures, including solids, fluids, and gases. Delve into the Bowen reaction series and learn how minerals crystallize at various temperatures. Additionally, the unit examines unicomponent and bicomponent systems, the phase rule, and the processes of equilibrium crystallization.