L1: Intro to and the classification of Ig Rocks Flashcards
igneous petrology: definition
study of magmas and the minerals that crystallize from them
What does this tool for classification include?
Texture/fabric of rock
field relations, hand specimen, and thin section
What does this tool for classification include?
Mineralogical
the mineral species present & their composition
what does this tool for classification include?
Modal Abundance
the measured/estimated volumetric proportions of minerals
What does this tool for classification include?
Chemical Composition
major oxide components (>0.1%) & the recalculated mineral mode
definition of this texture
Phaneritic
all crystals are visible to the naked eye (>1mm)
indicates slow cooling; intrusive and plutonic rocks
definition of this texture
Aphanitic
all crystals are too small to be visible to the naked eye
rapid cooling; extrusive and volcanic rocks
definition of this texture
Porphyritic
2 dominant grain sizes: the large phenocrysts and finer-grained groundmass
suggests multi-stage cooling history
equigranular
uniform grain sizes
definition of feldspathoids
Si-poor minerals similar to feldspars
examples of “foids”
Leucite, Nepheline, Sodalite
What rocks plot near P on QAPF?
anorthosite, gabbro, diorite
volcanic QAPF
aphanitic/glassy; (>10% crystals); ignores groundmass
Best method for classifying aphanitic/glassy rocks?
chemical composition