Classification of Igneous rocks (composition)

Question 1

How do we classify Igneous rocks?

Answer 1

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

Question 2

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

Answer 2

Modal Composition or Mode

Question 3

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

Answer 3

Normative Mineralogy

Question 4

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

Answer 4

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

Question 5

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

Answer 5

Ultrabasic

Question 6

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

Answer 6

basic

Question 7

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

Answer 7

Intermediate

Question 8

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

Answer 8

Acidic (silicic)

Question 9

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

Answer 9

Dark-colored Minerals

Question 10

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

Answer 10

Light-colored Felsic Minerals

Question 11

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

Answer 11

Ultramafic

Question 12

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

Answer 12

Mafic

Question 13

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

Answer 13

Intermediate

Question 14

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

Answer 14

Felsic

Question 15

> 90% Dark-colored crystalline mineral

Answer 15

Ultramafic

Question 16

70-90% Dark-colored crystalline mineral

Answer 16

Mafic

Question 17

40-70% Dark-colored crystalline mineral

Answer 17

Intermediate

Question 18

<40% Dark-colored crystalline mineral

Answer 18

Felsic

Question 19

Quartz ± Feldspar and/or magnesium orthopyroxene

Answer 19

SiO2 oversaturated

Question 20

Feldspar and/or Magnesium orthopyroxene only

Answer 20

SiO2 Saturated

Question 21

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

Answer 21

SiO2 undersaturated

Question 22

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

Answer 22

SiO2 undersaturated

Question 23

<30% Dark Minerals according to Shand Classification

Answer 23

Leucocratic

Question 24

30-60% Dark Minerals according to Shand Classification

Answer 24

Mesocratic

Question 25

60-90% Dark Minerals according to Shand Classification

Answer 25

Melanocratic

Question 26

>90% Dark Minerals according to Shand Classification

Answer 26

Hypermelanic

Question 27

<10% Dark Minerals according to Ellis Classification

Answer 27

Holofelsic

Question 28

10-40% Dark Minerals according to Ellis Classification

Answer 28

Felsic

Question 29

40-70% Dark Minerals according to Ellis Classification

Answer 29

Mafelsic

Question 30

70-90% Dark Minerals according to Ellis Classification

Answer 30

Mafic

Question 31

>90% Dark Minerals according to Ellis Classification

Answer 31

Ultramafic

Question 32

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

Answer 32

Peraluminous

Question 33

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

Answer 33

Subaluminous

Question 34

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

Answer 34

Metaluminous

Question 35

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

Answer 35

Peralkaline

Question 36

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

Answer 36

Peridotite

Question 37

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

Answer 37

Basalt

Question 38

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

Answer 38

Gabbro

Question 39

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.

Answer 39

Andesite

Question 40

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.

Answer 40

Diorite

Question 41

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.

Answer 41

granodiorite

Question 42

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.

Answer 42

Dacite

Question 43

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

Answer 43

Rhyolite

Question 44

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

Answer 44

Granite

Question 45

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

Answer 45

pumice

Question 46

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

Answer 46

Scoria

Question 47

non-crystalline rocks include those with glassy textures

Answer 47

Obsidian

Question 48

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

Answer 48

Tuff

Question 49

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

Answer 49

Extrusive (volcanic)

Question 50

igneous rocks formed at depth; typically phaneritic

Answer 50

Intrusive (plutonic)

Question 51

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.

Answer 51

hypabyssal rocks