Page 276 - Ultimate Visual Dictionary (DK)

GEOLOGY, GEOGRAPHY, AND METEOROLOGY
Igneous and BASALT COLUMNS

metamorphic rocks

IGNEOUS ROCKS ARE FORMED WHEN MAGMA (molten rock that originates from deep
beneath the Earth’s crust) cools and solidifies. There are two main types of igneous
rock: intrusive and extrusive. Intrusive rocks are formed deep underground where
magma is forced into cracks or between rock layers to form structures
such as sills, dikes, and batholiths. The magma cools slowly to Cinder Large eroded
cone lava flow
form coarse-grained rocks such as gabbro and pegmatite.
Cedar-tree
Extrusive rocks are formed above the Earth’s Butte laccolith
surface from lava (magma that has been Plug
ejected in a volcanic eruption). The molten
lava cools quickly, producing fine-grained
rocks such as rhyolite and basalt.
Metamorphic rocks are those that have
been altered by intense heat (contact
metamorphism) or extreme pressure
(regional metamorphism). Contact
metamorphism occurs when rocks are
changed by heat from, for example, an
igneous intrusion or lava flow. Regional
metamorphism occurs when rock is
crushed in the middle of a folding
mountain range. Metamorphic rocks can
be formed from igneous rocks, sedimentary
rocks, or even from other metamorphic rocks.
Cone
CONTACT METAMORPHISM
sheet
Metamorphic aureole (region where Ring
contact metamorphism occurs) dike
Hot Batholith
igneous Limestone Dike
intrusion
Shale Sill
Dike
Marble Slate IGNEOUS ROCK STRUCTURES swarm
(metamorphosed (metamorphosed Lopolith
limestone) shale)
REGIONAL METAMORPHISM EXAMPLES OF METAMORPHIC ROCKS
Pale
Mountain Slate, formed under Pale Dark mica Dark mineral calcite
range low pressure and feldspar band
Compression temperature
Compression

Schist, formed under
medium pressure and
Crust
temperature
Gneiss, formed under
Mantle high pressure and GNEISS FOLDED SCHIST SKARN
Magma temperature
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