Petrography

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What is a typical extinction angle for orthopyroxene?

Biaxial minerals have

2 optic axes and 3 indices of refraction

In XPL, when looking perpendicular to the principal; section, a triclinic mineral will show extinction at _____ locations during a complete rotation of the stage

4

What is the range of wavelengths for visible light?

400 to 700 µm

In which of the following modern locations would you be most likely to find active deposition of carbonate?

Bahamas

Which of the following is not a diagnostic mineral property?

Color

In Bowen's reaction series, the terms discontinuous and continuous refer to

Continuity of composition and discontinuity of structure

What two igneous minerals are found together?

Diopside and forsterite

Clinopyroxenes have more ____ than orthopyroxenes.

Fe and Mg

What are the maximum interference colors one should expect from a mineral with a birefringence of 0.001?

First-order gray

An isotropic mineral

Has no birefringence

Naturally occurring glass

Is isotropic Can be basaltic or rhyolitic Is mostly volcanic in origin Is not a mineral (all of these)

How can you tell a monzogranite from a monzonite?

Monzonite has less quartz

What is most important in determining the equilibrium mineralogy of a metamorphic rock?

P and T and composition

How do you tell quartz from K-feldspar in thin section?

Quartz sometimes shows undulatory extinction.

ripple marks are best described as

Sedimentary structures formed in the presence of a current

A porphyritic texture implies:

Slow cooling followed by rapid cooling

Plane-polarized light, upon interring anisotropic minerals

Splits into two vibration at right angles to each other with different velocities

In which crystal systems are the optical axes and the crystallographic axes of minerals aligned?

Tetragonal, hexagonal

If, when you raise the stage, a white line moves from the outer edge of a crystal to the inner edge, then

The crystal has a higher RI than its surrounding

20 quartz grains are observed in a thin section of a sandstone. None of them appear exactly the same in XPL. What is the best explanation for this observation?

The grains have different orientations relative to the plane of the thin section.

If a mineral causes light to slow down by 20% then

The wavelength must increase by 20%

What are the maximum interference colors one should expect from a mineral with a birefringence of 0.050?

Third-order orange or red

When does even a strongly anisotropic mineral show no birefringence?

When looking perpendicular to the circular section

What is the best way to determine the thickness of a thin section?

With the interference color of a known mineral

Should one use XPL or PPL to determine if a mineral is twinned?

XPL

Fractional crystallization of a basaltic magma will produce

a liquid with more SiO2 that it started with.

A geothermometer is

a mineral assemblage that can reveal the minimum temperature attained during heating

A sandstone is best described as

a rock composed of material from 2 to 0.625 mm in diameter

Which of the following is true? a. Diopside has inclined extinction b. SiO2-saturated rocks sometimes contain leucite c. Hornblende is common in obsidian d. Andesite has 45% SiO2 e. Monzogranite has higher birefringence than biotite

a. Diopside has inclined extinction

Which of the following statements about sedimentary rocks in general is false? a. They are composed exclusively of rocks and mineral particles produced from the weathering of older rocks b. biogenic sediments are produced by the life activities of plants and animals c. chemical processes alter minerals as rocks weather d. soluble ions are produced by weathering e. diagenesis can be thought of as very low grade metamorphism

a. They are composed exclusively of rocks and mineral particles produced from the weathering of older rocks

Which of the following terms best describes trilobite?

an example of an allochem

A fine-grained igneous rock with 61% SiO2, 1% K2O, and 2% Na2O is best called a

andesite

A pleochroic mineral must always be

anisotropic

Which of these is not an example of a typical cement mineral?

apatite

Which of the following lists is written in order of chemical stability on the ocean floor from least to most?

aragonite, low-Mg calcite, high-Mg calcite

________ is the Fe-rich end member of the clinopyroxenes

augite

A fine-grained igneous rock with 10% opx, 15%, plagioclase, and 75% groundmass is best called a

basalt

A metamorphic rock with mostly olivine, epidote, augite, and albite is most likely to have _____________ as its protolith.

basalt

________ often contains pleochroic halos

biotite

Rocks with lawsonite, glacophane, and albite are best categorized in the ________ facies.

blueschist

Which of the following metamorphic facies is diagnostic of subduction zones?

blueschist

A metamorphic rock contains dolomite, garnet, phlogopite, diopside (avg. grain size 2.5 mm). What is the protolith?

calcareous sandstone

Lithification requires

cementation

Which of the following lists is given in increasing grade of metamorphism?

chlorite, biotite, staurolite

Which of the following lists is written in decreasing order of grain size?

conglomerate, sandstone, siltstone

Which of the following metamorphic rocks experienced the highest pressure?

eclogite

________ is the Fe-rich end member of the olivines

fayalite

What is the most prominent feature of rocks formed by regional metamorphism?

foliation

Which of the following terms best describes ooids?

formed in the surf zone

Which of the following terms best describes dolomite?

found more in ancient rocks than modern sediments

What is the coarse grained equivalent of basalt?

gabbro

A coarse-grained igneous rock with 20% quartz, 20% plagioclase, 20%, Kspar, 20% biotite, and 20% hornblende is best called a

granodiorite

Rocks with quartz, K-spar, sillimanite, and garnet are best categorized in the ________ facies.

granulite

Rocks with quartz, chlorite, and plagioclase are best categorized in the ________ facies.

greenschist

Rocks with quartz, muscovite, plagioclase feldspar, biotite, and chlorite are best categorized in the ________ facies.

greenschist

A mineral with a refractive index of 1.7 mounted in epoxy with a refractive index of 1.55 will show

high positive relief

To find the birefringence (δ) of a mineral, look for a mineral grain with the

highest interference color

Rocks with quartz and andalusite are best categorized in the ________ facies.

hornfels

Allochems include

intraclasts and fossils

Which of the following scenarios would result in the smallest zone of contact metamorphism?

intrusion of an rhyolitic dike 5 m wide

A Geologist suffers from a black eye after yelling "Gneiss!!!" to a classmate, who happened to be sunning on a large boulder. The geologist really meant to tell the classmate that the rock they were laying on

is a high-grade, silicate-rich, mineralogically banded metamorphic rock

The original bedding in a sedimentary rock

is only preserved in low-grade metamorphic rocks

A metamorphic rock contains Quartz, Kfsp, kyanite, biotite, plag (avg. grain size 4.3 mm). What is the most likely name for this rock?

kyanite gneiss

A metamorphic rock with mostly calcite and dolomite is most likely to have _____________ as its protolith.

limestone

Which of the following metamorphic rocks cannot form from a shale?

marble

Isograds are line of equal

metamorphic assemblage

Which of the following terms best describes fine-grained carbonate mud?

micrite

Which of the following pairs from the Folk and Dunham classifications describe essentially the same rock?

micrite and mudstone

Which of the following metamorphic rocks experienced the highest temperature?

migmatite

A highly rounded, well-sorted sediment with 40% feldspar and 60% quartz is

mineralogically immature and texturally mature

For which of the following sediments would compaction be most important in the process of lithification?

mud

In the Dunham classification of carbonates a mud-supported rock with less than 10% grains is called a

mudstone

In PPL an orthorhombic mineral will show extinction at _____ locations during a complete rotation of the stage

no

A limestone is best described as

none of the above

Mud cracks are best described as

none of the above

________ is a rock we know erupted at a very high temperature

obsidian

A coarse-grained igneous rock with 40% pyroxene, 40% olivine, and 20%, plagioclase is best called a

olivine gabbro

A mineral with a 2V angle of 0° is

orthorhombic, trigonal, or tetragonal

In the Dunham classification of carbonates a grain-supported rock with some mud is called a

packstone

10% melt of ____ will produce basalt

peridotite

Another name for dunite is

peridotite

In PPL, a mineral changes its color when rotated. This is called

pleochroism

Which of the following groups of mineral characteristics are observed best (or only) in PPL?

pleochroism, color, relief

What two minerals are never found in the same igneous rock?

quartz and forsterite

Which of the following lists contain minerals that are highly resistant to chemical weathering?

quartz, tourmaline, and zircon

A metamorphic rock contains quartz, plagioclase, chlorite (avg. grain size 0.55 mm). What is the most likely name for this rock?

quartzite

Assimilation is important in the production of

rhyolite

What is the fine-grained equivalent of granite?

rhyolite

________ is a common inclusion in quartz

rutile

A metamorphic rock contains quartz, plagioclase, chlorite (avg. grain size 0.55 mm). What is the protolith?

sandstone

A metamorphic rock with mostly dolomite, talc and tremolite is most likely to have _____________ as its protolith.

sandy limestone

A metamorphic rock with mostly wollastonite, calcite and garnet is most likely to have _____________ as its protolith.

sandy limestone

A metamorphic rock contains quartz, Kfsp, kyanite, muscovite, plag (avg. grain size 4.3 mm). What is the protolith?

shale

A metamorphic rock with mostly kyanite, muscovite, staurolite, and quartz is most likely to have _____________ as its protolith.

shale

A metamorphic rock with mostly quartz, biotite, plagioclase, and andalusite is most likely to have _____________ as its protolith.

shale

Which of the following lists is given in increasing grade of metamorphism?

shale, schist, migmatite

Which of the following pairs of minerals are not likely to be found in the same metamorphic rock?

sillimanite and chlorite

Zircon is a tetragonal mineral. Is it likely to have

straight extinction

Isotherms are bent down in

subduction zones

Metasomatism is

the change of the bulk composition of a rock during metamorphism

A shale is best described as

the most common sedimentary rock

Which of the following is not used to classify metamorphic rocks?

the texture of the parent rock

The process of lithification is

the transformation of loose sediment in to sedimentary rock

In a uniaxial mineral, when the fast ray travels parallel to the c-axis, we call that mineral

uniaxial positive

The 2Vx angle of olivine can vary from 45 to 100°. This variation is caused by

variation in composition

________ is extensively used in geochronology

zircon

________ often produces pleochroic halos

zircon

How is the φ parameter for describing grain size calculated?

φ = log2(D), where D is the grain diameter in mm


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