Geology lesson 8 igneous rocks

Vesicular

Vesicular

________- bubbles were trapped in cooling lava, extrusive, ex: scoria.

Obsidian

________- dark colored volcanic glass, conchodial fracture, rhyolitic.

Pegmatitic

________- very coarse grained texture, intrusive.

Porphyritic

________- two distinct crystal sizes, intrusive or extrusive, indicates 2 stages of cooling.

Aphanitic

________- fine grained texture, extrusive, volcanic, cooled near /at surface.

Phaneritic

________- coarse grained texture, crystals we can see.

Pumice

________- rock foam, light weight, floats, mostly holes, usually felsic.

Yellowstone

________ caldera- form from collapse of large area after the discharge of large volumes of silica- rich pumice and ash, complex history.

Shield

________ volcano- largest volcanoes, gentle slopes, mafic (basaltic) magma, non explosive, associated with mantle plumes.

Lava domes

________ - small dome with steep sides, in the vent of stratovolcano after explosive eruption, highly vicious magma, common in ring of fire.

Continental caldera

________- circular steep sided depressions with a diameter> 1km.

Volcano

________- vent or chimney which transfers molten rock known as magma from the depth to the earths surface.

Stratovolcanoes

________- composite, conical shapes, high viscosity, can be extremely explosive, common in ring of fire.

Hawaiian caldera

________- form gradually from collapse of the summit of a shield volcano following the subterranean drainage of the central magma chamber.

Crater lake caldera

________- form from collapse of the summit of large composite volcanos following an eruption.

phaneritic

coarse grained texture, crystals we can see

slow rate of cooling

fewer but larger crystals

fast rate of cooling

many small crystals

coarse grained textures indicate

magmas that slowly cooled deep underground

porphyritic

two distinct crystal sizes, intrusive or extrusive, indicates 2 stages of cooling

pumice

rock foam, light weight, floats, mostly holes, usually felsic

glassy

extrusive, looks like a block of colored glass, cooling was extremely fast, no crystals

obsidian

dark colored volcanic glass, conchodial fracture, rhyolitic

pyroclastic

extrusive, mixture of rock fragments, pumice, and volcanic ash

volcano

vent or chimney which transfers molten rock known as magma from the depth to the earths surface

shield volcano

largest volcanoes, gentle slopes, mafic (basaltic) magma, non explosive, associated with mantle plumes

stratovolcanoes

composite, conical shapes, high viscosity, can be extremely explosive, common in ring of fire

lava domes

small dome with steep sides, in the vent of stratovolcano after explosive eruption, highly vicious magma, common in ring of fire

mount st. Helens

stratovolcano

cinder cones (scoria cones)

small, only 100 m in diameter, 200m high, cone shaped, accumulation of tephra, formed when lava meets groundwater, low to intermediate explosiveness

cinder cone

Paricutin volcano, Mexico

continental caldera

circular steep sided depressions with a diameter > 1km

crater lake caldera

form from collapse of the summit of large composite volcanos following an eruption

Hawaiian caldera

form gradually from collapse of the summit of a shield volcano following the subterranean drainage of the central magma chamber

Yellowstone caldera

form from collapse of large area after the discharge of large volumes of silica-rich pumice and ash, complex history