Question 1

How might hydrothermal ore genesis occur?
A) Hot seawater rushes through porous rocks and crystallizes on contact with the rocks.
B) Cold seawater meets hot circulating hydrothermal fluids and precipitation occurs.
C) Two rock masses meet at a hydrothermal vent and the heat of the water dissolves ions from both masses. They recrystallize when they are carried to cooler water.
D) Hot water from a hydrothermal vent dissolves ions from one rock mass and reprecipitates them as ore in cooler water.

Accepted Answer

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A) Hot...

Question 2

Why do metamorphic rocks exist at the surface?

Accepted Answer

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Question 3

If a rock containing kyanite and andalusite were to undergo a decrease in pressure, what must happen to temperature in order for that rock to continue to have stable kyanite and andalusite?
A) temperature must increase
B) temperature must decrease
C) temperature must stay the same
D) It is impossible for it to continue to have stable kyanite and andalusite.

Accepted Answer

Kyanite and andalusite are metamorphic minerals that form under high pressure and low temperature conditions. If the pressure on the rock decreases, the rock will be out of its equilibrium conditions, and the kyanite and andalusite may transform into other minerals. However, if the temperature decreases at the same time, the rock may remain in its stable kyanite and andalusite phase. Therefore, in order to keep the stable kyanite and andalusite, the temperature must decrease.

Question 4

How do geologists know how to determine the stability of minerals?

Accepted Answer

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Question 5

What is metamorphism?

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Question 6

A well know example of a paired metamorphic belt occurs in
A) Japan.
B) England.
C) Mexico.
D) Australia.

Accepted Answer

The paired metamorphic belt in Japan is known as the Sanbagawa belt and the Sambagawa is paired with the Ryoke Belt.

Question 7

Which of the following pairs of index minerals do not overlap in metamorphic grade?
A) chlorite and pyroxene
B) biotite and garnet
C) staurolite and kyanite
D) amphibole and sillimanite

Accepted Answer

Chlorite and pyroxene do not overlap in metamorphic grade; chlorite is stable in low-grade metamorphic conditions, while pyroxene is stable in higher-grade conditions.

Question 8

What is the role of pressure in metamorphism?

Accepted Answer

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Question 9

If a rock containing kyanite, sillimanite, and andalusite were to undergo an increase in pressure, what must happen to temperature in order for that rock to continue to have stable kyanite, sillimanite, and andalusite?
A) temperature must increase
B) temperature must decrease
C) temperature must stay the same
D) It is impossible for it to continue to have stable kyanite, sillimanite, and andalusite.

Accepted Answer

Kyanite, sillimanite, and andalusite are polymorphs of Al2SiO5, meaning they have the same chemical composition but different crystal structures. They form under different conditions of temperature and pressure, and it is not possible for all three to be stable at the same time under a change in conditions.

Question 10

Which type of metamorphism occurs exclusively at lower pressures?
A) Regional metamorphism occurs exclusively at lower pressures.
B) Contact metamorphism occurs exclusively at lower pressures.
C) Hydrothermal metamorphism occurs exclusively at lower pressures.
D) All three types of metamorphism occur exclusively at lower pressures.

Accepted Answer

Contact metamorphism occurs when rock comes into contact with magma or lava at relatively low pressures. Regional metamorphism and hydrothermal metamorphism can occur at higher pressures.

Question 11

If a rock containing kyanite and sillimanite were to undergo an increase in pressure, what must happen to temperature in order for that rock to continue to have stable kyanite and sillimanite?
A) temperature must increase
B) temperature must decrease
C) temperature must stay the same
D) It is impossible for it to continue to have stable kyanite and sillimanite.

Accepted Answer

Kyanite and sillimanite are polymorphs of Al2SiO5, meaning they have the same chemical composition but different crystal structures due to their formation under different conditions of temperature and pressure. Kyanite is stable at high pressure and lower temperature, while sillimanite is stable at high temperature. If pressure increases, temperature must also increase to maintain a condition where both kyanite and sillimanite can coexist stably.

Question 12

What role does temperature play in metamorphism?

Accepted Answer

The answer of What role does temperature play in metamorphism?...

Question 13

Although muscovite, feldspar and quartz are not considered useful as index minerals, which of the following situations could be useful in determining the grade of metamorphism in a region?
A) the coexistence of muscovite, feldspar and quartz
B) the disappearance of rocks containing muscovite and quartz
C) the coexistence of feldspar and quartz
D) the disappearance of rocks containing quartz

Accepted Answer

The disappearance of rocks containing muscovite and quartz can indicate higher-grade metamorphism, as these minerals break down or transform at higher temperatures and pressures.

Question 14

When do black smokers occur?
A) during plate tectonics movement
B) during underwater volcanic reactions
C) components dissolve below the seafloor, but then precipitate when they contact cold water
D) components squeezed from beneath the sea floor dissolve upon contact of cold water

Accepted Answer

Black smokers occur when mineral-rich components dissolve below the seafloor and then precipitate when they come into contact with cold ocean water, forming chimney-like structures.

Question 15

What role does fluid play in metamorphism?

Accepted Answer

The answer of What role does fluid play in metamorphism?...

Question 16

Which of the following pairs of index minerals do not overlap in metamorphic grade?
A) chlorite and biotite
B) amphibole and garnet
C) staurolite and sillimanite
D) kyanite and pyroxene

Accepted Answer

Staurolite and sillimanite do not overlap in metamorphic grade. Staurolite is commonly found in low-to-medium grade metamorphic rocks, while sillimanite is found in high-grade metamorphic rocks. Therefore, the presence of both minerals together can help geologists determine the range of metamorphic grades present in a rock.

Question 17

Which process makes it the most difficult to trace metamorphic rocks to their parent rocks?
A) fluid metamorphism
B) regional metamorphism
C) contact metamorphism
D) melting

Accepted Answer

Fluid metamorphism can occur in open systems where fluids from various sources can infiltrate the parent rock and cause changes. This can make it difficult to trace the metamorphic rock back to its exact parent rock. Regional and contact metamorphism are generally more localized and easier to trace, while melting is not a metamorphic process at all.

Question 18

If a rock containing andalusite and sillimanite were to undergo an increase in pressure, what must happen to temperature in order for that rock to continue to have stable andalusite and sillimanite?
A) temperature must increase
B) temperature must decrease
C) temperature must stay the same
D) It is impossible for it to continue to have stable andalusite and sillimanite.

Accepted Answer

Andalusite and sillimanite are both polymorphs of the mineral Al2SiO5, meaning they have the same chemical composition but different crystal structures. As pressure increases on the rock, it will want to change into a denser structure to accommodate the pressure. Sillimanite is the densest of the three polymorphs (including kyanite), and at high enough pressure, andalusite will transform into sillimanite. However, such a transformation would require breaking and forming many new chemical bonds within the mineral, which is an endothermic process (it requires heat/energy). Therefore, in order for the rock to maintain stable andalusite and sillimanite as pressure increases, the temperature must decrease to provide the necessary energy for the transformations to occur.

Question 19

When a shale metamorphoses into a slate why do some slates contain muscovite and some slates contain chlorite?
A) The chlorite slates form at different pressures than the muscovite slates.
B) The chlorite slates have a different composition than the muscovite slates.
C) The chlorite slates form at different temperatures than the muscovite slates.
D) The chlorite slates form at different temperatures and pressures than the muscovite slates.

Accepted Answer

The presence of muscovite or chlorite in slates depends on the original composition of the shale that underwent metamorphism. Different minerals form from different precursor materials under similar conditions of pressure and temperature.

Question 20

A gneiss containing kyanite and sillimanite most likely formed from a metamorphosed
A) limestone.
B) mafic igneous rock.
C) coal.
D) shale.

Accepted Answer

Kyanite and sillimanite are minerals that form under high pressure and temperature conditions, such as during the metamorphism of shale. Limestone and coal are not likely to contain these minerals, and mafic igneous rocks are not typically involved in the formation of gneiss with kyanite and sillimanite.

Quiz 6: Formation of Metamorphic Rocks

How might hydrothermal ore genesis occur?

Why do metamorphic rocks exist at the surface?

If a rock containing kyanite and andalusite were to undergo a decrease in pressure, what must happen to temperature in order for that rock to continue to have stable kyanite and andalusite?

How do geologists know how to determine the stability of minerals?

What is metamorphism?

A well know example of a paired metamorphic belt occurs in

Which of the following pairs of index minerals do not overlap in metamorphic grade?

What is the role of pressure in metamorphism?

If a rock containing kyanite, sillimanite, and andalusite were to undergo an increase in pressure, what must happen to temperature in order for that rock to continue to have stable kyanite, sillimanite, and andalusite?

Which type of metamorphism occurs exclusively at lower pressures?

If a rock containing kyanite and sillimanite were to undergo an increase in pressure, what must happen to temperature in order for that rock to continue to have stable kyanite and sillimanite?

What role does temperature play in metamorphism?

Although muscovite, feldspar and quartz are not considered useful as index minerals, which of the following situations could be useful in determining the grade of metamorphism in a region?

When do black smokers occur?

What role does fluid play in metamorphism?

Which of the following pairs of index minerals do not overlap in metamorphic grade?

Which process makes it the most difficult to trace metamorphic rocks to their parent rocks?

If a rock containing andalusite and sillimanite were to undergo an increase in pressure, what must happen to temperature in order for that rock to continue to have stable andalusite and sillimanite?

When a shale metamorphoses into a slate why do some slates contain muscovite and some slates contain chlorite?

A gneiss containing kyanite and sillimanite most likely formed from a metamorphosed