Earth Science Quiz #17

Igneous Rocks

Rocks that form from the cooling crystallization of magma and lava

Plutonic

Rocks that form underground creating larger crystal size since it cools slower

Volcanic Igneous Rocks

Igneous rocks that form above the earth’s surface

Aphanitic

Crystal size generally too small to see with the unaided eye

Phaneritic

crystals generally large enough to be seen with the unaided eye

pegmatitic

texture characterized by extremely large crystal size of frequently gem minerals

Porphyritic

Texture characterized by two distinct crystal or grain sized, the larger crystals called “phenocrysts” formed plutonically while the finer grained ground mass cooled volcanically

Vesicular

texture characterized by trapped air bubbles

Glassy

The texture that forms when the lava cools so quickly that the crystals aren’t allowed to form

Aa

Rough, angular, sharp, jagged

Pahoehoe

smooth, ropey

Intrusion (Plutons)

intrusive igneous rock that forms and cools underground

Batholith

A large less that 100 sq² km irregularly shaped pluton that is often a vertical extension of a batholith

Stock

extremely large great that 100 sq² km, irregularly shaped igneous plutons

Dike

A tabular or sheet like intrusion that is discordant (at an angle to) the surrounding rock layers

Sill

Tabular or sheet like intrusion that is concordant to (parallel with) the surrounding rock layers

Volcanic Neck

a solidified column of igneous rock that forms when magma cool or crystallizes in the central vent of a volcano and is later exposed by erosion of the softer flank material of the volcano

Laccolith

Mushroom shaped intrusion formed when magma squeezes between rock layers and uplifts the overlying rock layers