Igneous Classification Flashcards
Also called as the MAFIC INDEX. It is also the proportion of mafic minerals in the total population of felsic and mafic minerals.
Color Index (CI)
What is the formula for the Color Index?
CI = %Mafic Minerals / %Felsic Minerals + %Mafic Minerals x 100
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.
Point Count Analysis
The first norm classification devised by Cross, Iddings, Pirsson, and Washington.
CIPW Norm
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.
IUGS Classification
SHAND CLASSIFICATION: for rocks with <30% dark colored minerals.
Eg. Granite
Leucocratic
SHAND CLASSIFICATION: for rocks with 30-60% dark colored minerals.
Eg. Diorite
Mesocratic
SHAND CLASSIFICATION: for rocks with 60-90% dark colored minerals.
Eg. Gabbro
Melanocratic
SHAND CLASSIFICATION: for rocks with >90% dark colored minerals.
Eg. Peridotite
Hypermelanic
ELLIS CLASSIFICATION: for rocks with <10% dark colored minerals.
Holofelsic
ELLIS CLASSIFICATION: for rocks with 10-40% dark colored minerals.
Eg. Granite
Felsic
ELLIS CLASSIFICATION: for rocks with 40-70% dark colored minerals.
Eg. Diorite
Mafelsic (Intermediate)
ELLIS CLASSIFICATION: for rocks with 70-90% dark colored minerals.
Eg. Gabbro
Mafic
ELLIS CLASSIFICATION: for rocks with >90% dark colored minerals.
Eg. Peridotite
Ultramafic
NORMATIVE CLASSIFICCATION: SILICA
Chemistry: SiO₂ Oversaturated
Key Minerals: Quartz and Felspars, and/or Mg-Orthopyroxene
Peralimunous
NORMATIVE CLASSIFICCATION: SILICA
Chemistry: SiO₂ Saturated
Key Minerals: Felsdpars, and/or Mg-Orthopyroxene only
Metaluminous
NORMATIVE CLASSIFICCATION: Silica
Chemistry: SiO₂ undersaturated
Key Minerals: Forsterite Olivine (Mg-rich), nepheline, leucite, and other feldspathoids & feldspars, and or orthopyroxene minerals, excluding quartz.
Subaluminous and Peralkaline
NORMATIVE CLASSIFICCATION: Aluminous Oxide
Chemistry: Al₂O₃ > CaO + Na₂O + K₂O
Key Minerals: Muscovite, Corundum, Topaz, Garnet, Tourmaline, Biotite, Cordierite, Andalusite, and Biotite
Peralimunous
NORMATIVE CLASSIFICCATION: Aluminous Oxide
Chemistry: Na₂O + K₂O < Al₂O₃ < CaO + Na₂O + K₂O
Key Minerals: Hornblende, Epidote, Melilite, Biotite, and Pyroxene
Metaluminous
NORMATIVE CLASSIFICCATION: Aluminous Oxide
Chemistry: Al₂O₃ = Na₂O + K₂O
Key Minerals: Olivine, Orthopyroxene, and Clinopyroxene
Subaluminous
NORMATIVE CLASSIFICCATION: Aluminous Oxide
Chemistry: Al₂O₃ > Na₂O + K₂O
Key Minerals: Aegirine, Riebeckite, Arfvedsonite, Aenigmatite, Astrophyllite, Columbite, and Pyrochlore
Peralkaline
What does the acronym QAPF mean?
Q - quartz and Silica
A - Alkali Felspar
P - Plagioclase Feldspar
F - Feldspathoids
A quantitative analysis that determines the abundance of a component of a material.
Normalization
What is the formula for normalization?
Q, A, P, F = %Minerals of Q, A, P, F / Summation of QAPF x 100%
