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Petrology and Mineralogy
Mock Exam
Part 2
1. The following comprise carbonate rocks except:
a. sparite
b. micrite
c. allochems
d. biolithic elements
e. none of the above
2. Mineralogical scheme based on the percentage of minerals based either on megascopic or microscopic observations is referred to as:
a. modal
b. norm
c. petrographic analysis
d. petrochemical scheme
e. none of the above
3. Igneous rocks containing grains that are too small to be resolved optically but are visible with an electron microscope and can be identified by XRD are/have:
a. microcrystalline
b. cryptocrystalline
c. intersertal textures
d. intergranular textures
e. none of the above
4. The following can be a protolith of greenschist except:
a. phyllite
b. chert
c. basalt
d. slate
e. none of the above
5. Particle with phi size between 4 to -1 are considered as:
a. boulder
b. cobble
c. pebble
d. sand
e. silt
6. Plutonic rock made up of 75% clinopyroxene and 25% orthopyroxene.
a. wehrlite
b. harzburgite
c. websterite
d. lherzolite
e. none of the above
7. What is the term for a metamorphic texture where prismatic grains with preferred orientations predominate:
a. nematoblastic
b. lepidoblastic
c. granoblastic
d. poikiloblastic
e. basaltoophitic
8. In optically ______________ uniaxial crystals, subtraction occurs at right angles to the direction of the slow ray in the accessory.
a. positive
b. negative
c. neutral
9. “Black jack” refers to:
a. galena
b. sphalerite
c. bornite
d. siderite
e. none of the above
10. An igneous texture that develops by hydration of obsidian on fracture surfaces that are exposed to moisture in the atmosphere or to meteoric water is called:
a. spherulitic texture
b. perlitic texture
c. pegmatitic texture
d. seriate texture
e. none of the above
11. Parallel to subparallel alignment of minerals produce this texture in igneous rocks.
a. Seriate
b. Glomeroporphyritic
c. Trachytic
d. cumulophyric
e. none of the above
12. A rudite composed of poorly sorted, mud to gravel-size sediment, commonly with angular clasts is called:
a. paraconglomerate
b. breccias
c. diamictite
d. orthoconglomerate
e. none of the above
13. Thick chert deposits are usually formed in:
a. marine environment above the carbonate compensation depth (CCD)
b. marine environment below the CCD
c. lacustrine environment
d. paludal environment
e. none of the above
14. Large clinopyroxenes partially to completely enclose smaller euhedral plagioclase define this texture in igneous rocks:
a. ophitic
b. subophitic
c. pilotaxitic
d. poikilitic
15. Clast-supported conglomerates are also referred to as:
A. oligomictic conglomerates
b. polymictic conglomerates
c. orthoconglomerate
d. paracongglomerate
e. none of the above
16. Particle with -6 to -8 phi size is:
a. Pebble
b. Cobble
c. Boulder
d. Silt
e. Sand
17. Volcanic rock made up of 70% orthoclase and 30% plagioclase.
a. trachyte
b. rhyolite
c. latite
d. andesite
e. none of the above
18. The crystal is ______if it is bounded entirely or almost entirely by crystal faces formed by growth in situ:
a. xenoblastic
b. porphyroblastic
c. poikiloblastic
d. idioblastic
e. none of the above
19. An optical property determined in thin section by the Becke Line test.
a. relief
b. oblique illumination
c. birefringence
d. index of refraction
e. none of the above
20. Which among the minerals do not contain nickel as a cation?
a. pentlandite
b. millerite
c. nickeline
d. chloanthite
e. none of the above
21. An igneous texture defined by spherical to ellipsoidal clusters of radiating fibrous alkali feldspars and a polymorph of SiO2 as a result from devitrification is called:
a. spherulitic texture
b. myrmekitic texture
c. intergranular texture
d. perlitic texture
e. none of the above
22. An igneous fabric wherein glass shards and pumice lapilli are flattened by compaction into disks oriented more or less parallel to the depositional surface.
a. pilotaxitic
b. seriate
c. eutaxitic
d. trachytic
e. none of the above
23. The Wentworth Scale is only used to classify clastic sedimentary rocks. This statement is:
a. true
b. false
c. not necessarily true
24. Concentrically laminated carbonate structures of less than2 mm diameter are called:
a. oolites
b. pisolites
c. oncolites
d. peloids
e. none of the above
25. This refers to the cumulative changes that particles go through as it is produced by weathering and is transported to a final site of deposition.
a. sorting
b. sphericity
c. maturity
d. diagenesis
e. none of the above
26. Quartz arenite will likely become this rock when metamorphosed:
a. chert
b. quartzite
c. chlorite schist
d. quartz muscovite schist
e. none of the above
27. Texture typical of basalt and consists of randomly oriented microlitic plagioclases and abundant, more equant pyroxenes, Fe-Ti and in some rocks, olivines that form a tightly interlocking mosaic.
a. intergranular
b. felsitic
c. intersertal
d. ophitic
e. subophitic
28. Metamorphic texture defined by equidimensional generally xenoblastic crystals of approximately equal size:
a. nematoblastic
b. lepidoblastic
c. granoblastic
d. lepidoblastic
e. poikiblastic
29. Which among the minerals do not contain manganese as a cation?
a. Rhodonite
b. Romanechite
c. Rhodochrosite
d. Pyrolusite
e. none of the above
30. Wurtzite is a polymorph of _____________.
a. Sphalerite
b. Galena
c. Tridymite
d. Siderite
e. Molybdenite
31. Which of the following minerals cannot occur as cement in sedimentary rocks?
a. quartz
b. calcite
c. clay
d. iron oxide
e. none of the above
32. Igneous rocks containing 45-52% silica fall under this igneous rock classification.
a. felsic
b. intermediate
c. mafic
d. ultramafic
e. none of the above
33. The following diagenetic processes occur in sandstones except:
a. compaction and pressure dissolution
b. silica cementation
c. hematite pigmentation
d. clay authigenesis
e. none of the above
34. Igneous rocks having 30 to 60% dark minerals are classified based on color index as :
a. leucocratic
b. melanocratic
c. mesocratic
d. hypermelanic
e. none of the above
35. The following can be a protolith of gneiss except:
a. schist
b. slate
c. phyllite
d. shale
e. none of the above
36. If the ray vibrating in the principal plane is the slow ray, the uniaxial crystal is said to be:
a. positive
b. negative
c. no conclusion can be drawn
37. Fragments of melt that quenched to glass are called:
a. vitroclasts
b. accidental clasts
c. cognate clasts
d. b and c
e. none of the above
38. The cumulative changes that particles go through as it is produced by weathering and is transported to a final site of deposition are a reflection of rock’s ________.
a. degree of sorting
b. degree of weathering
c. maturity
d. sphericity
e. none of the above
39. Plutonic rock made up of 50% quartz, 15% plagioclase; 10% hornblende.
a. Quartz diorite
b. Tonalite
c. Granodiorite
d. Quartz monzodiorite
e. None of the above
40. The two broad black curves or brushes which mark the areas of extinction are known as: a. interference figures.
b. isogyres
c. indicatrices
d. isohyaths
e. none of the above
41. A term synonymous to anhedral shape of crystals.
a. xenomorphic
b. hypidiomorphic
c. subhedral
d. b and c
e. none of the above
42. Igneous rocks having less than 45% silica content are classified as:
a. basic
b. acidic
c. ultrabasic
d. intermediate
e. none of the above
43. Metamorphic facies with typical assemblage of labradorite + clinopyroxene + orthopyroxene + quartz basic igneous rocks:
a. granulite
b. blueschist
c. eclogite
d. greenschist
e. none of the above
44. Which is NOT TRUE of carbonate rocks?
a. They are usually formed in areas far from siliciclastic sedimentation
b. Most primary carbonate sediments form as biogenic particles
c. Most carbonate production occurs as chemical or biochemical precipitation from clear, warm, shallow water
d. Chemical precipitation can produce non-skeletal carbonate grains of various sizes e. none of the above
45. _______are likely products of extended periods of sediment reworking.
a. quartz arenite
b. arkosic arenite
c. litharenite
d. greywacke
e. none of the above
BONUS QUESTION:
The optic sign of a biaxial mineral is conveniently determined with the mineral in the ____ position with a quartz wedge:
a. 45o
b. 60o
c. 30o
d. 75o
e. none of the above
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