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Geology Board Exam Day 2 > Classification of Igneous rocks (composition) > Flashcards

Classification of Igneous rocks (composition) Flashcards

1
Q

How do we classify Igneous rocks?

A

Based on Composition
Based of Fabric and Texture
Base on Field relation

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2
Q

Most Straight forward approach to determining rock mineralogy that involves visually identifying the minerals and determining their percentage by volume.

A

Modal Composition or Mode

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3
Q

an indirect scheme using data derived from chemical analysis of a rock sample. this is commonly used in aphanitic or glassy volcanic rocks.

A

Normative Mineralogy

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4
Q

Why is Normative Mineralogy used in Aphanitc and glassy volcanic rocks?

A

because the modal mineral composition of these rocks can not be determined.

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5
Q

Rock group with <45% weighted percent silica (SiO2)

A

Ultrabasic

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6
Q

Rock group with 45-52% weighted percent silica (SiO2)

A

basic

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7
Q

Rock group with 52-66% weighted percent silica (SiO2)

A

Intermediate

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8
Q

Rock group with >66% weighted percent silica (SiO2)

A

Acidic (silicic)

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9
Q

Generally enriched in the elements iron and magnesium and are referred to as Ferromagnesian or Mafic minerals

A

Dark-colored Minerals

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10
Q

Depleted in Ferromagnesian elements and are generally enriched in elements such as silicon, oxygen, potassium, and sodium

A

Light-colored Felsic Minerals

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11
Q

Rocks that are Dark or greenish in color that’s rich in olivine and may or may not contain pyroxene or amphibole

A

Ultramafic

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12
Q

Dark-colored rocks containing pyroxene and amphibole. it may or may not contain some olivine and biotite

A

Mafic

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13
Q

Grayish to salt and pepper colored rocks rich in plagioclase and amphibole. It may or may not contain amounts of Biotite and Quartz.

A

Intermediate

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14
Q

Light-colored or red rock rich in potassium feldspar and quartz. It may or may not contain some amount of Biotite or Muscovite

A

Felsic

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15
Q

> 90% Dark-colored crystalline mineral

A

Ultramafic

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16
Q

70-90% Dark-colored crystalline mineral

A

Mafic

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17
Q

40-70% Dark-colored crystalline mineral

A

Intermediate

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18
Q

<40% Dark-colored crystalline mineral

A

Felsic

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19
Q

Quartz ± Feldspar and/or magnesium orthopyroxene

A

SiO2 oversaturated

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20
Q

Feldspar and/or Magnesium orthopyroxene only

A

SiO2 Saturated

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21
Q

Forsterite olivine, nepheline, leucite, and other feldspathoids ± feldspar and/or orthopyroxene minerals. excluding quartz

A

SiO2 undersaturated

22
Q

Forsterite olivine, nepheline, leucite, and other feldspathoids ± feldspar and/or orthopyroxene minerals. excluding quartz

A

SiO2 undersaturated

23
Q

<30% Dark Minerals according to Shand Classification

A

Leucocratic

24
Q

30-60% Dark Minerals according to Shand Classification

A

Mesocratic

25
Q

60-90% Dark Minerals according to Shand Classification

A

Melanocratic

26
Q

> 90% Dark Minerals according to Shand Classification

A

Hypermelanic

27
Q

<10% Dark Minerals according to Ellis Classification

A

Holofelsic

28
Q

10-40% Dark Minerals according to Ellis Classification

A

Felsic

29
Q

40-70% Dark Minerals according to Ellis Classification

A

Mafelsic

30
Q

70-90% Dark Minerals according to Ellis Classification

A

Mafic

31
Q

> 90% Dark Minerals according to Ellis Classification

A

Ultramafic

32
Q

Igneous rock based on AlO concentration:
Al2O3 > CaO + Na2O +K2O

A

Peraluminous

33
Q

Igneous rock based on AlO concentration:
Al2O3 = Na2O +K2O

A

Subaluminous

34
Q

Igneous rock based on AlO concentration:
Na2O +K2O < Al2O3 < CaO + Na2O +K2O

A

Metaluminous

35
Q

Igneous rock based on AlO concentration:
Al2O3 < Na2O +K2O

A

Peralkaline

36
Q

A very dark-colored rock, depleted in SiO 2 and commonly enriched in the minerals pyroxene, olivine, amphibole, and plagioclase. Ultramafic plutonic rocks occur in Earth’s Mantle

A

Peridotite

37
Q

A fine-grained dark-colored (mafic), SiO 2- poor (Basic) rock rich in plagioclase, pyroxene, and olivine

A

Basalt

38
Q

A coarse-grained dark-colored, silica-poor rock rich in plagioclase, pyroxene, and olivine

A

Gabbro

39
Q

Fine-grained gray-colored to salt and pepper-colored rocks rich in hornblende, pyroxene, and plagioclase. Andesite and diorite contain more than half to almost two-thirds SiO 2.

A

Andesite

40
Q

A coarse-grained gray-colored to salt and pepper-colored rocks rich in hornblende, pyroxene, and plagioclase. Andesite and diorite contain more than half to almost two-thirds SiO 2.

A

Diorite

41
Q

A coarse-grained light-colored (felsic) rock, containing approximately two-thirds SiO2, rich in plagioclase, alkali feldspar, and quartz, and also contains small amounts of hornblende and biotite.

A

granodiorite

42
Q

A fine-grained light-colored (felsic) rock, containing approximately two-thirds SiO2, rich in plagioclase, alkali feldspar, and quartz, and also contains small amounts of hornblende and biotite.

A

Dacite

43
Q

A fine-grain light-colored (felsic) rock containing more than two-thirds SiO 2 (silicic or acidic) and rich in quartz, alkali feldspar with small percentages of plagioclase and biotite

A

Rhyolite

44
Q

A coarse-grain light-colored (felsic) rock containing more than two-thirds SiO 2 (silicic or acidic) and rich in quartz, alkali feldspar with small percentages of plagioclase and biotite

A

Granite

45
Q

light-colored non-crystalline vesicular rocks characterized by the absence of crystals.

A

pumice

46
Q

dark-colored non-crystalline vesicular rocks characterized by the absence of crystals.

A

Scoria

47
Q

non-crystalline rocks include those with glassy textures

A

Obsidian

48
Q

Non-crystalline rocks that are enriched in rock
pyroclastic fragments that are volcanic ash to gravel size.

A

Tuff

49
Q

magma emplaced onto the surface of the Earth as coherent lava flows or as fragmental deposits. These rocks are typically aphanitic and glass

A

Extrusive (volcanic)

50
Q

igneous rocks formed at depth; typically phaneritic

A

Intrusive (plutonic)

51
Q

formed at intermediate depths not clearly distinct from those of volcanic and plutonic rocks. They can have fabric similar to that of plutonic and volcanic
rocks.

A

hypabyssal rocks

Geology Board Exam Day 2 (17 decks)

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