Igneous Rocks Flashcards
Granite
Coarse interlocking crystal matrix,
Euhedral
Potassium Feldspar, Quartz, Sodium, Amphibole, Mica
Formed Intrusively
Rhyolite
Aphanitic
Feldspar, Quartz, no Amphibole (Maybe Biotite)
Formed Extrusively
Diorite
Coarse Grained
Plagioclase, Amphibole, Pyroxene, Quartz
Formed Intrusively
Gabbro
Coarse Grained
Calcium, Plagioclase, Pyroxiene, Olivine
Formed Intrusively
Tuff
Aphanitic with Phenocrysts
Formed Extrusively from products of an explosive volcanic eruption
Often contains debris from bedrock and volcanic ash. Composition varies
Felsic
Aphanitic
Small Crystals
Phaneritic
Larger Crystals
Pegmatitic
Very coarse crystals, larger than 3 centimeters
Phenocrysts
Relatively large crystal embedded in an aphanitic matrix.
Pegmatite
Form during the final stage of a magma’s crystallization.
Composed almost entirely of crystals at lease 1 cm in diameter
Aplite
Forms during the final stage of a magma’s crystallization.
Intrusive rock
Aphanitic
Felsic
Light in color
Mafic
Dark in color
Scoria
Vesicular Basaltic lava with small vesicles
Mafic
Pumice
Vesicular volcanic rock containing volcanic glass and sometimes crystals
Felsic
Vesicle
Cavity formed in volcanic rock by entrapment of a gas bubble during solidification
Ignimbrite
Rock that shows direction of flow
Rock is formed from pyroclastic flow
Porphyry
Rock that consists of large grained crystals (phenocrysts) embedded in a fine grained matrix
Groundmass
The matrix of rock that is finer grained than the larger crystals that are embedded.
Xenolith
A rock fragment which becomes enveloped in a larger rock during the latter’s development and hardening.
(Inclusions)
Pyroclastic
Fragments of rock of explosive origin,
Volcanic Ash, Obsidian, and Pumice
Lava Flow
Stream or sheet of molten or solidified lava
occurs on the surface
Contact Metamorphism
Metamorphism due to contact with or proximity to an igneous intrusion
Dike
Vertical Igneous Intrusion
Sill
Horizontal Igneous Intrusion
Lapilli
Volcanic rock materials which are formed when magma is ejected by a volcano.
2-64 mm in diameter
Means “Little Stones” in Latin
Chill Zone
Border zone in intrusive igneous rocks that are fine grained because of rapid cooling.
Reaction Rim
A border of secondary minerals formed at the margin of the primary grain in an igneous or metamorphic rock.
Euhedral
Crystals that are well formed with sharp faces
Growth occurs in a free environment, unconstrained by adjacent minerals.
Anhedral
Crystals that are not well formed
This crystal growth occurs in a competitive environment with no free space for the formation of crystal faces
