Petrology Midterm
Emplacement - ANSWERSWhere igneous rocks form
Plutonic - ANSWERSIgneous rocks formed underground
Shallow/Epizonal <5km
Middle/mesozonal 5-15km
Deep/catazonal >15km
Volcanic - ANSWERSIgneous rocks formed at the surface, dispersal near to far from vent,
Can be lava or pyroclastic
Hypabyssal(subvolcanic) - ANSWERSIgneous rocks w/ textural characteristics like volcanic rocks
but emplaced in plutonic setting, shallow <1-2km
Igneous textures descriptors - ANSWERSDegree of crystallinity (0-100% xls)
Grain size and shape (euhdral ect.)
Geometric arrangement (fabric)
Igneous texture controlling perameters - ANSWERSComp of magma
Rate of cooling and cooling history
Nucleation and growth rate
Ascent history
Order of crystallization
Petrogenic history
, Porphyritic - ANSWERSBig phenocryst in fine grain ground mass
Euhedral - ANSWERSIdiomorhpic, fully formed crystal shape
Anhedral - ANSWERSXenomorphic, no distinct crystal shape
Subhedral - ANSWERSSome crystal shape, between euhedral and anhedral
Aphanitic - ANSWERSNo visible crystal, like obsidian
Phaneretic - ANSWERSVisible large crystals
Textures within crystal grain - ANSWERSMineral inclusion, mineral exsolution, intergrowth,
mineral zonation
TAS - ANSWERSTotal alkali vs silica content diagram, main Chem classification diagram
Distinguishes btw subalkaline and alkalic
AFM ternary diagram - ANSWERSAlkali, FeO, MgO, distinguishes btw alkaline and tholeiitic
Basis mineralogical classification - ANSWERSType and proportion of minerals dependent on
comp of magma
Modal mineralogy - ANSWERSMineral proportion determined by petrographic analysis, the
more glass and smaller crystal = less accurate
Emplacement - ANSWERSWhere igneous rocks form
Plutonic - ANSWERSIgneous rocks formed underground
Shallow/Epizonal <5km
Middle/mesozonal 5-15km
Deep/catazonal >15km
Volcanic - ANSWERSIgneous rocks formed at the surface, dispersal near to far from vent,
Can be lava or pyroclastic
Hypabyssal(subvolcanic) - ANSWERSIgneous rocks w/ textural characteristics like volcanic rocks
but emplaced in plutonic setting, shallow <1-2km
Igneous textures descriptors - ANSWERSDegree of crystallinity (0-100% xls)
Grain size and shape (euhdral ect.)
Geometric arrangement (fabric)
Igneous texture controlling perameters - ANSWERSComp of magma
Rate of cooling and cooling history
Nucleation and growth rate
Ascent history
Order of crystallization
Petrogenic history
, Porphyritic - ANSWERSBig phenocryst in fine grain ground mass
Euhedral - ANSWERSIdiomorhpic, fully formed crystal shape
Anhedral - ANSWERSXenomorphic, no distinct crystal shape
Subhedral - ANSWERSSome crystal shape, between euhedral and anhedral
Aphanitic - ANSWERSNo visible crystal, like obsidian
Phaneretic - ANSWERSVisible large crystals
Textures within crystal grain - ANSWERSMineral inclusion, mineral exsolution, intergrowth,
mineral zonation
TAS - ANSWERSTotal alkali vs silica content diagram, main Chem classification diagram
Distinguishes btw subalkaline and alkalic
AFM ternary diagram - ANSWERSAlkali, FeO, MgO, distinguishes btw alkaline and tholeiitic
Basis mineralogical classification - ANSWERSType and proportion of minerals dependent on
comp of magma
Modal mineralogy - ANSWERSMineral proportion determined by petrographic analysis, the
more glass and smaller crystal = less accurate
