Podcast
Questions and Answers
What is the phase rule for binary systems when pressure is constant?
What is the phase rule for binary systems when pressure is constant?
What is the composition of the crystals in equilibrium with the melt at Tliquidus?
What is the composition of the crystals in equilibrium with the melt at Tliquidus?
Which of the following best describes a binary system?
Which of the following best describes a binary system?
What does the equilibrium relationship in a binary phase diagram indicate about plagioclase and its coexisting melt?
What does the equilibrium relationship in a binary phase diagram indicate about plagioclase and its coexisting melt?
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What factors are kept constant while constructing binary phase diagrams?
What factors are kept constant while constructing binary phase diagrams?
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In a binary phase diagram, which axes are typically represented?
In a binary phase diagram, which axes are typically represented?
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At Tsolidus, what is the composition of the melt in equilibrium with the crystals?
At Tsolidus, what is the composition of the melt in equilibrium with the crystals?
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During the crystallization of magma in a binary phase diagram, which of the following occurs?
During the crystallization of magma in a binary phase diagram, which of the following occurs?
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Which component interaction is represented in the plagioclase system example?
Which component interaction is represented in the plagioclase system example?
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How many phases can a binary system typically consist of?
How many phases can a binary system typically consist of?
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What is the overall trend observed in the plagioclase system concerning solid and liquid composition?
What is the overall trend observed in the plagioclase system concerning solid and liquid composition?
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What does the axis labeled 'X' in a binary phase diagram typically represent?
What does the axis labeled 'X' in a binary phase diagram typically represent?
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What is a characteristic of a one-phase binary system?
What is a characteristic of a one-phase binary system?
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Which phase has the highest compositional value of An in the given plagioclase system?
Which phase has the highest compositional value of An in the given plagioclase system?
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What is the significance of Tsolidus in the context of the plagioclase system?
What is the significance of Tsolidus in the context of the plagioclase system?
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In the plagioclase system, what does it mean that 'plag is always more calcic than coexisting melt'?
In the plagioclase system, what does it mean that 'plag is always more calcic than coexisting melt'?
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At which point is the melt (An75) observed in the plagioclase system?
At which point is the melt (An75) observed in the plagioclase system?
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What does Tliq/sol represent in the context of the binary phase diagram?
What does Tliq/sol represent in the context of the binary phase diagram?
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What does zoned plagioclase in granite indicate about the cooling process of magma?
What does zoned plagioclase in granite indicate about the cooling process of magma?
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What is implied by oscillatory zoning in plagioclase crystals?
What is implied by oscillatory zoning in plagioclase crystals?
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Which parameters might change during cooling to explain reversals in zoning patterns?
Which parameters might change during cooling to explain reversals in zoning patterns?
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What is a characteristic of the extinction angle in zoned crystals?
What is a characteristic of the extinction angle in zoned crystals?
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How does zoning in rocks like andesite relate to magma cooling?
How does zoning in rocks like andesite relate to magma cooling?
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At what temperature does the melt solidify when producing An75 plagioclase?
At what temperature does the melt solidify when producing An75 plagioclase?
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Which composition represents the final plagioclase composition during equilibrium crystallization?
Which composition represents the final plagioclase composition during equilibrium crystallization?
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What happens to the composition of plagioclase as it continuously reacts with melt?
What happens to the composition of plagioclase as it continuously reacts with melt?
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What is the initial melt composition when starting the crystallization process?
What is the initial melt composition when starting the crystallization process?
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During equilibrium crystallization, the composition of plagioclase crystals is equal to what?
During equilibrium crystallization, the composition of plagioclase crystals is equal to what?
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At what crystallization stage does plagioclase become An0?
At what crystallization stage does plagioclase become An0?
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Which phase is present at the liquidus temperature during the crystallization process?
Which phase is present at the liquidus temperature during the crystallization process?
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What characterizes the plagioclase composition in relation to the coexisting melt?
What characterizes the plagioclase composition in relation to the coexisting melt?
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Study Notes
Binary Phase Diagrams Overview
- Binary systems involve only two components and typically exhibit a small number of phases (2 to 4).
- Relevant to crystallization processes from magma, focusing on melt (L) and crystals (Xls).
Phase Rule and Diagrams
- Given composition (C) = 2, the maximum variance (F) can be 3 in a single phase system.
- Pressure is kept constant; changes are made to temperature and composition.
- The phase rule simplifies to F = C - P + 1 under constant pressure conditions.
Plagioclase System Example
- The plagioclase system demonstrates complete solid solution where components mix thoroughly.
- Major components: Na+, Ca2+, and Al3+.
- Evolving compositions in plagioclase from melt lead to zoned crystals in igneous rocks.
Equilibrium vs. Fractional Crystallization
- In equilibrium crystallization, plagioclase continuously reacts with the melt, maintaining composition balance.
- Final plagioclase composition equals bulk and initial melt composition, solidifying at ~1100°C.
- Fractional crystallization can cause zoned plagioclase due to variations in melt and crystal compositions as cooling progresses.
Crystallization Phases and Composition
- Initial phase: melt (An75) transitions to various phases as temperature decreases.
- As temperature decreases, compositions change:
- Liquidus: melt (An75), plagioclase (An90)
- Tliq/sol: melt (An65), plagioclase (An85)
- Tsolidus: melt (An50), plagioclase (An75)
- Final composition at Tfinal: plagioclase (An75).
Zoning in Plagioclase Crystals
- Zoning is characterized by variable extinction angles reflecting different compositions.
- Oscillatory zoning indicates fluctuations in An (anorthite) and Ab (albite) percentage during crystallization.
- Changes in other parameters like composition (X) or pressure (P) during cooling explain fluctuations in crystal formation.
Application and Importance
- Understanding binary phase diagrams aids in predicting mineral stability and composition in geological processes.
- Key in igneous and metamorphic petrology for interpreting rock formation and evolution.
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Description
Explore the complexities of binary phase diagrams and their significance in crystallisation from magma. This quiz focuses on systems with two components and the variance in phases. Understand how to illustrate these systems through three-dimensional diagrams.