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Correlation: DAY 2 > Correlation: Phase Equilibria and Phase Diagrams > Flashcards

Correlation: Phase Equilibria and Phase Diagrams Flashcards

1
Q

Compositionally and physically distinctive (solid, liquid, gas)

A

Phase

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2
Q

Chemical reactions between phases

A

Phase equilibria

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3
Q

Stable/metastable/unstable states

A

Equilibrium

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4
Q

Governs phase equilibria

A

Laws of Thermodynamics

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5
Q

Visual representation of equilibria

A

Phase diagrams

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6
Q

One component system (P-T diagram)

A

Unary systems

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7
Q

Two component system (T-composition)

A

Binary Systems

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8
Q

Three component system (triangular)

A

Ternary Systems

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9
Q

Melt same composition as mineral

A

Congruent Melting

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10
Q

Melt different composition from mineral

A

Incongruent melting

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11
Q

Minerals melt together at lower T

A

Eutectics

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12
Q

Minerals with multiple components

A

Solid solutions

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13
Q

What is the relationship between atomic bonding and mineral melting points?

A

Stronger bonds = higher melting points

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14
Q

Why do minerals have specific melting temperatures?

A

Temperature where kinetic energy overcomes atomic bonds

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15
Q

How does water affect the melting temperature of minerals?

A

Water lowers melting temperatures (flux melting)

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16
Q

How do pressure-temperature (P-T) diagrams help us understand mineral melting?

A

P-T diagrams show how melting temperatures change with pressure (and therefore depth in the Earth).

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17
Q

Differentiate minerals and homogenous substances from rocks

A

Minerals and homogeneous substances are phases, but rocks are not

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18
Q

What occurs when substances transform between states.

A

Phase changes

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19
Q

Describes how phases relate to each other

A

Phase Equilibria

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20
Q

What illustrate conditions where different phases are stable.

A

Phase Diagrams

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21
Q

Govern rules of phase changes, predict mineral stability and interpret mineral assemblages

A

Laws of Thermodynamics

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22
Q

Shows conditions where one phase transforms to another (like graphite to diamond

A

Reaction Line

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23
Q

Line representing temperature changes with depth in Earth

A

Geotherm

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24
Q

No exchange of matter or energy with surroundings

A

Isolated System

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25
Q

Energy exchange allowed, but composition remains fixed

A

Closed System

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26
Q

Both matter and energy can be exchanged with the environment

A

Open System

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27
Q

What are the three states of equilibrium, and how do they relate to rocks and minerals?

A

Stable: Lowest energy state, no change will occur
Metastable: Temporary equilibrium, change is likely
Unstable: System is actively changing

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28
Q

How does Le Chatelier’s Principle describe chemical systems?

A

Systems counteract changes to restore equilibrium

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29
Q

What is Gibbs free energy (ΔG), and how does it dictate phase stability?

A

Energy form that determines stability; phases with lower ΔG are more stable.

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30
Q

How does entropy (S) relate to phase changes?

A

Higher entropy favors phases that are less ordered (liquids over solids, gases over liquids).

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31
Q

How does pressure impact phase stability?

A

Higher pressure favors denser phases.

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32
Q

Independent of sample size

A

Intensive Variables

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33
Q

Depend on the amount of material

A

Extensive Variables

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34
Q

P-T Diagram

A

Pressure-induced phase changes at constant composition
Analyzing single-mineral melting behavior.

35
Q

T-X Diagram

A

Temperature-induced phase changes across a range of compositions
Understanding mixed composition minerals and partial melting

36
Q

Define the term “phase” in the context of minerals and rocks.

A

A compositionally and physically distinct substance (solid, liquid, gas

37
Q

Describe the difference between a P-T diagram and a T-X diagram

A

P-T: Shows phase changes with pressure and temperature (for a fixed composition)
T-X: Shows phase changes with temperature and composition (at a fixed pressure)

38
Q

What is the difference between stable, metastable, and unstable equilibrium?

A

Stable: Lowest energy state, no change will occur
Metastable: Temporary equilibrium, change is likely
Unstable: System is actively changing

39
Q

How does a mineral’s atomic bonding relate to its melting point?

A

Stronger bonds = higher melting point

40
Q

What is the difference between a “component” and a “phase” in a chemical system?

A

A component is a chemical element or compound that makes up a system. A phase is the physical form (solid, liquid, gas) the components take.

41
Q

How are the different phases of silica represented on this phase diagram? SiO2 ang diagram. Wala koy diagram pang pro lng pwede hahahaha

A

Each solid polymorph has its own field labeled with its name; liquid is labeled “L”.

42
Q

What does a line (or curve) on a phase diagram tell us?

A

It shows the exact pressure and temperature conditions where two phases can coexist in equilibrium.

43
Q

Why are minerals like stishovite so rare on the Earth’s surface?

A

They form under very high pressures only found deep within the Earth or at meteorite impact sites.

44
Q

If I find a rock with coesite in it, what does that tell me about its history?

A

It formed under higher pressures than normal surface conditions – either a meteorite impact or deep in the mantle.

45
Q

What happens to normal quartz if I heat it up under normal surface conditions?

A

It transforms through several different solid polymorphs before ultimately melting

46
Q

Mg2SiO4 Diagram: What does the sloped line on the diagram tell us?

A

That’s the melting curve for forsterite, showing the temperature and pressure where solid and liquid can coexist.

47
Q

How does forsterite’s behavior under low pressure differ from quartz?

A

Unlike quartz, it doesn’t transform into other solid polymorphs before melting.

48
Q

What happens to forsterite at extremely high pressure?

A

It forms different, denser mineral structures (modified spinel, spinel, then perovskite and periclase)

49
Q

Based on this diagram, at what depths within the Earth could we expect to find the “spinel” form of forsterite?

A

Only at depths greater than 400 km because that’s where pressures are high enough.

50
Q

H2O System: What is a ‘critical point’, and what happens to water when we pass it?

A

Above the critical point, the distinction between liquid and gas disappears, and we have a supercritical fluid.

51
Q

What is a ‘triple point’? Why is this point interesting for the water system?

A

A triple point is where solid, liquid, AND gas phases can all coexist. For water, it occurs at very low pressures.

52
Q

These are systems with two chemical components, which can be represented by a horizontal T-X composition diagram.

A

Binary Systems

53
Q

‘building blocks’ and can be elements or compounds. They don’t need to be minerals themselves (e.g., MgO).

A

Components

54
Q

The horizontal axis can represent composition in ________ or ________

A

weight percent (wt%) or mole percent (mol%).

55
Q

Eutectic Crystallization Diagram: What components make up this system, and how are they represented on the diagram?

A

The components are diopside (CaMgSi2O6) and anorthite (CaAl2Si2O8), plotted at the ends of the composition axis.

56
Q

What does the red region of the diagram represent?

A

The melt field – temperatures and compositions where the substance is entirely liquid

57
Q

What is the significance of points like “1,394 °C” and “1,553 °C” on the sides?

A

These are the melting temperatures of the pure components (pure diopside or anorthite melts).

58
Q

What is a ‘eutectic point’, and how do we identify it on the diagram?

A

It’s the lowest temperature where a melt can exist (labeled “E”) and is the point where the two curves touch.

59
Q

What is the ‘eutectic composition’, and why is it special?

A

The composition at the eutectic point (here, An42Di58). A melt with this exact composition melts/crystallizes entirely at a single temperature.

60
Q

What are the ‘liquidus’ and ‘solidus’ lines, and what do they represent?

A

Liquidus: The boundary above which everything is liquid. Solidus: The boundary below which everything is solid.

61
Q

What does the gray area between the liquidus and solidus represent?

A

Two-phase fields, where a melt and crystals coexist. The labels tell you which mineral crystallizes along with the melt.

62
Q

An intrusive rock made mostly of plagioclase and pyroxene that has the composition of common basalt.
This rock has an ophitic texture.

A

Diabase

63
Q

Plagioclase laths surrounded by later crystallizing pyroxene/olivine

A

Ophitic Texture

64
Q

If you see ophitic texture in a rock, what does it tell you about how that rock cooled and crystallized?

A

Plagioclase crystallized first over some time, then remaining melt hit eutectic point and everything solidified quickly

65
Q

Fine grained, light-colored, plagioclase surrounds large dark colored pyroxene crystals.

A

Gabbro

66
Q

Compare the gabbro to the diabase description. How does the melt composition relate to the order of crystallization

A

Gabbro’s melt was diopside-rich, diabase’s was anorthite-rich, affecting which mineral formed first

67
Q

As a melt cools towards the eutectic, how does its composition change?

A

It follows the liquidus curve, becoming more enriched in the component that hasn’t been crystallizing (here, diopside).

68
Q

What is a supercritical fluid, and how does this relate to water at very high pressures?

A

A supercritical fluid is a substance above its critical point where liquid and gas phases become indistinguishable. Water becomes a supercritical fluid at high pressure and temperature

69
Q

Could you find ice, liquid water, and steam all together on the H2O phase diagram? Explain.

A

Yes! They can coexist at the triple point, where the melting and boiling curves intersect

70
Q

On a binary T-X diagram, what do the liquidus and solidus represent?

A

Liquidus: Boundary above which everything is liquid. Crystallization STARTS when cooling melt hits this line.Solidus: Boundary below which everything is solid. Crystallization is COMPLETE once temperature drops below this

71
Q

Explain the lever rule. Why does the segment closest to the melt field represent the amount of SOLID present?

A

The longer the ‘solid’ side of the segment gets, the more solid has crystallized

72
Q

Eutectic diagrams are important because they demonstrate(3)

A

Lower Melting Temperatures: Mixtures of minerals melt at lower temperatures than individual minerals, increasing the likelihood of magma formation.
Extended Crystallization Range: Magmas can cool significantly before fully solidifying, leading to diverse mineral compositions.
Melt-Rock Differentiation: Partial melting or crystallization creates chemically distinct melts and rocks, driving Earth’s chemical evolution.

73
Q

Describe Incongruent Melting

A

Melt produced has a different composition than the original mineral.
A new solid mineral is formed alongside the melt.
Occurs over a temperature range, leading to partial melts.

74
Q

What does a liquidus line represent on a phase diagram?
A. The temperature at which a mineral completely melts
B. The boundary between a liquid field and a liquid + solid field
C. The composition of the first melt formed from a rock
D. The maximum temperature where a solid phase can exist

A

B

75
Q

What is the key characteristic of a eutectic point?
A. It’s where three different phases can coexist
B. It represents the congruent melting of a single mineral
C. It’s the lowest temperature at which any melt is stable in the system
D. It’s always located at exactly 50% composition in a binary diagram

A

C

76
Q

If a melt cools and its composition follows the liquidus down to the eutectic, what happens at the eutectic temperature?
A. All of the remaining melt crystallizes at once
B. One mineral disappears, and another one starts crystallizing
C. The melt composition changes abruptly
D. Crystallization cannot continue below the eutectic

A

A

77
Q

Which of these can you directly determine by looking at a T-X (temperature-composition) phase diagram?
A. The exact temperature a specific rock began to melt
B. The proportions of melt and minerals present at a specific temperature
C. How the density of a melt changes with cooling
D. The appearance (texture) of rocks formed in this system

A

B

78
Q

A melt cools within a system that has a peritectic point. What happens when the temperature reaches the peritectic?
A. No more crystallization can happen.
B. Any existing crystals will completely dissolve back into the melt.
C. One solid mineral is replaced by a different one.
D. The melt’s composition changes abruptly.

A

C

79
Q

A mineral has a “triple point” on a phase diagram. This means:
A. It has three different polymorphs.
B. It melts incongruently at three different temperatures.
C. Three phases (solid, liquid, gas) of this mineral can coexist under specific conditions.
D. It can form three different eutectic mixtures

A

C

80
Q

A melt of intermediate composition starts to cool within a binary eutectic system. Which of the following is TRUE?
A. The first crystals to form will have the same composition as the initial melt.
B. Two different minerals will crystallize simultaneously at a single temperature.
C. The composition of the remaining melt changes as crystallization proceeds.
D. No crystals will form until the temperature reaches the solidus.

A

C
Explanation: In a eutectic system, the first mineral to crystallize will be whichever one is stable on the relevant side of the diagram. As this happens, the remaining melt gets depleted in that component, shifting its composition along the liquidus.

81
Q

Consider the quartz-leucite phase diagram. A rock containing only K-feldspar is heated. What will be present at 1200 °C?
A. Leucite crystals and a silica-rich melt
B. Only K-feldspar (melting hasn’t begun)
C. K-feldspar crystals and a melt of K-feldspar composition
D. A melt with a composition between K-feldspar and the peritectic

A

A
Explanation: 1200°C is above the incongruent melting point of K-feldspar, so some melt will be present. The melt will be more silica-rich than the original K-feldspar, and leucite will be the new solid phase.

82
Q

You apply the lever rule to determine the proportions of minerals and melt at a specific temperature within a binary eutectic system. Your result is that there is 70% melt and 30% of a mineral. This means the original melt composition must have been:
A. Exactly the same as the mineral that crystallized.
B. Somewhere between the mineral composition and the eutectic point.
C. Closer to the pure OTHER component on the diagram.
D. Impossible to tell without more information.

A

B
Explanation: The lever rule works like a seesaw. If the ‘melt’ side is much longer, the original composition had to be closer to the mineral that crystallized out. It must fall along that segment of the liquidus

83
Q

Consider the effect of pressure on phase diagrams. Which is generally true?
A. Increasing pressure always raises the melting points of minerals.
B. Increasing pressure tends to expand the stability fields of denser phases.
C. Phase diagrams with eutectics will no longer have eutectics at very high pressure.
D. Pressure has little effect on systems involving mostly liquids and gases.

A

B
Explanation: Pressure favors denser phases. This means higher pressure often raises melting temperatures (solid -> liquid = less dense), and can shift boundaries between different solid polymorphs. Eutectics may persist, but shift in composition.

Correlation: DAY 2 (2 decks)

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