Igneous Classification

Question 1

Also called as the MAFIC INDEX. It is also the proportion of mafic minerals in the total population of felsic and mafic minerals.

Answer 1

Color Index (CI)

Question 2

What is the formula for the Color Index?

Answer 2

CI = %Mafic Minerals / %Felsic Minerals + %Mafic Minerals x 100

Question 3

A much more accurate method of obtaining a mode for any course-grained rock done by moving a thin section incrementally on a grid system such that at least 400 minerals are tabulated for each thin section.

Answer 3

Point Count Analysis

Question 4

The first norm classification devised by Cross, Iddings, Pirsson, and Washington.

Answer 4

CIPW Norm

Question 5

A classification by the IUGS based on the modal concentration of Quartz, Alkali Felspars, Plagioclase Feldspars, and Feldspathoids, which applies for igneous rocks with >10% felsic minerals and <90% mafic minerals (M) content by volume.

Answer 5

IUGS Classification

Question 6

SHAND CLASSIFICATION: for rocks with <30% dark colored minerals.

Eg. Granite

Answer 6

Leucocratic

Question 7

SHAND CLASSIFICATION: for rocks with 30-60% dark colored minerals.

Eg. Diorite

Answer 7

Mesocratic

Question 8

SHAND CLASSIFICATION: for rocks with 60-90% dark colored minerals.

Eg. Gabbro

Answer 8

Melanocratic

Question 9

SHAND CLASSIFICATION: for rocks with >90% dark colored minerals.

Eg. Peridotite

Answer 9

Hypermelanic

Question 10

ELLIS CLASSIFICATION: for rocks with <10% dark colored minerals.

Answer 10

Holofelsic

Question 11

ELLIS CLASSIFICATION: for rocks with 10-40% dark colored minerals.

Eg. Granite

Answer 11

Felsic

Question 12

ELLIS CLASSIFICATION: for rocks with 40-70% dark colored minerals.

Eg. Diorite

Answer 12

Mafelsic (Intermediate)

Question 13

ELLIS CLASSIFICATION: for rocks with 70-90% dark colored minerals.

Eg. Gabbro

Answer 13

Mafic

Question 14

ELLIS CLASSIFICATION: for rocks with >90% dark colored minerals.

Eg. Peridotite

Answer 14

Ultramafic

Question 15

NORMATIVE CLASSIFICCATION: SILICA
Chemistry: SiO₂ Oversaturated

Key Minerals: Quartz and Felspars, and/or Mg-Orthopyroxene

Answer 15

Peralimunous

Question 16

NORMATIVE CLASSIFICCATION: SILICA
Chemistry: SiO₂ Saturated

Key Minerals: Felsdpars, and/or Mg-Orthopyroxene only

Answer 16

Metaluminous

Question 17

NORMATIVE CLASSIFICCATION: Silica
Chemistry: SiO₂ undersaturated

Key Minerals: Forsterite Olivine (Mg-rich), nepheline, leucite, and other feldspathoids & feldspars, and or orthopyroxene minerals, excluding quartz.

Answer 17

Subaluminous and Peralkaline

Question 18

NORMATIVE CLASSIFICCATION: Aluminous Oxide
Chemistry: Al₂O₃ > CaO + Na₂O + K₂O

Key Minerals: Muscovite, Corundum, Topaz, Garnet, Tourmaline, Biotite, Cordierite, Andalusite, and Biotite

Answer 18

Peralimunous

Question 19

NORMATIVE CLASSIFICCATION: Aluminous Oxide
Chemistry: Na₂O + K₂O < Al₂O₃ < CaO + Na₂O + K₂O

Key Minerals: Hornblende, Epidote, Melilite, Biotite, and Pyroxene

Answer 19

Metaluminous

Question 20

NORMATIVE CLASSIFICCATION: Aluminous Oxide
Chemistry: Al₂O₃ = Na₂O + K₂O

Key Minerals: Olivine, Orthopyroxene, and Clinopyroxene

Answer 20

Subaluminous

Question 21

NORMATIVE CLASSIFICCATION: Aluminous Oxide
Chemistry: Al₂O₃ > Na₂O + K₂O

Key Minerals: Aegirine, Riebeckite, Arfvedsonite, Aenigmatite, Astrophyllite, Columbite, and Pyrochlore

Answer 21

Peralkaline

Question 22

What does the acronym QAPF mean?

Answer 22

Q - quartz and Silica
A - Alkali Felspar
P - Plagioclase Feldspar
F - Feldspathoids

Question 23

A quantitative analysis that determines the abundance of a component of a material.

Answer 23

Normalization

Question 24

What is the formula for normalization?

Answer 24

Q, A, P, F = %Minerals of Q, A, P, F / Summation of QAPF x 100%

Question 25

QAPF MINERALOGY: What are the minerals associated with Q (Quartz and Silica)?

Answer 25

Quartz, Tridymite, Cristobalite, Coesite, Stishovite

Question 26

QAPF MINERALOGY: What are the minerals associated in A (Alkali Feldspars)?

Answer 26

Orthoclase, Anorthoclase, Microcline, Sanidine, Perthite, Albite

Question 27

QAPF MINERALOGY: What are the minerals associated in P (Plagioclase Felspars)?

Answer 27

Anorthite, Bytownite, Labradorite, Andesine, Oligoclase, Albite, and Scapolite

Question 28

QAPF MINERALOGY: What are the minerals associated in F (Feldspathoids)?

Answer 28

Nepheline, Sodalite,Nosean, Cancrinite, Leucite, Analcite, Hauyne, and Kalsilite

Question 29

QAPF MINERALOGY: What are the minerals associated in M (Mafic-related Minerals)?

Tip: This is used for differentiating Diorite, Gabbro, and Anorthosite.

Answer 29

Olivine, Pyroxene, Amphiboles, Micas, Melilite, Garnet, Epidote, Calcite, Allanite, Zircon, Apatite, and Sphene

Question 30

GABBROIC MINERALOGY: What are the minerals associated with “Plag”?

Answer 30

Anorthite, Bytownite, Labradorite, Andesine, Oligoclase, Albite, and Scapolite

Question 31

GABBROIC MINERALOGY: What are the minerals associated with “Plag”?

Answer 31

Anorthite, Bytownite, Labradorite, Andesine, Oligoclase, Albite, and Scapolite.

Question 32

GABBROIC MINERALOGY: What are the minerals associated with “Px”?

Answer 32

Aegirine, Augite, Diopside, Omphacite, Spodumene, Enstatite, Hypersthene, Wollastonite

Question 33

GABBROIC MINERALOGY: What are the minerals associated with “OL”?

Answer 33

Forsterite and Fayalite

Question 34

GABBROIC MINERALOGY: What are the minerals associated with “Hbl”?

Answer 34

Hornblende

Question 35

ULTRAMAFIC MINERALOGY: What are the minerals associated with “OL”?

Answer 35

Forsterite and Fayalite

Question 36

ULTRAMAFIC MINERALOGY: What are the minerals associated with “Cpx”?

Answer 36

Aegirine, Augite, Diopside, Omphacite, Spodumene

Question 37

ULTRAMAFIC MINERALOGY: What are the minerals associated with “Opx”?

Answer 37

Enstatite and Hypersthene

Question 38

ULTRAMAFIC MINERALOGY: What are the minerals associated with “Hbl”?

Answer 38

Hornblende