IGNEOUS ROCK TERMINOLOGY Flashcards
Work sheet from lab 5
Phaneritic (def, formation, identification, example)
def: crystals are so course that individual minerals can be distinguished with the naked eye.
formation: intrusive rocks that cooled slowly enough to allow significant crystal growth. Mainly formed in plutonic situations.
identification: large crystals visible without magnification.
example: granite, diorite.
Porphyritic (def, formation, identification)
def: varying crystal size in one rock.
formation: cooled in two stages, first very slowly so larger crystals form and then much quicker forming the finer groundmass around crystals.
identification: crystals imbedded in finer matrix
Aphanitic (def, formation, identification, example)
def: made of crystals that can’t be seen by the naked eye.
formation: extrusive rocks that cooled quickly resulting in minimal crystal growth.
identification: small crystals that need to be magnified to be seen.
examples: basalt, andesite
Vesicular (def, formation, identification, example)
def: a small cavity in a glassy or aphanitic igneous rock.
formation: expansion of a bubble of gas or steam during solidification of rocks.
identification: many pitted cavities at rock surface or inside.
examples: Pumice and Scoria
Volcaniclastic (def, formation, identification)
def: clastic rock containing volcanic material as well as terrigenous debris.
formation: segments of volcanic rock becoming included in other rocks due to transportation, redeposition or weathering.
identification: large and or many different clasts.
Nucleation
Formation of stable start of lattice. Forms faster at lower temperatures although not too low
Growth
Growth of lattice. Forms faster at higher temperatures due to ease of diffusion
Course grained rock formation
formation due to slow cooling lots of growth with few nuclei
Fine grained rock formation
formation due to fast cooling with little growth and many nuclei
Glass or amorphous solid formation
formation due to very rapid cooling which means there is little growth and few formation of nuclei
Mafic
made up of magnesium and iron and is less then half silica
Intermediate
made up of just over half silica and a mixture
Felsic
made up of predominantly silica
gabbro
course grained mafic
basalt
fine grained mafic
