EARTH SCIENCEROCKS
IGNEOUS, SEDIMENTARY,
AND METAMORPHIC
WHAT IS A ROCK? A rock is a group of minerals that are
bound together. Rocks are MIXTURES because they have
varying percentages of different minerals Rocks are classified according to how they
were formed.
THREE GENERAL TYPES OF ROCKS:
Igneous rocks—formed by the cooling and hardening of magma from inside the earth.
Sedimentary rocks—formed by the compaction and cementing of layers of sediments
Metamorphic rocks—formed by the effects of heat and pressure on other rocks
ROCK CYCLE Rocks form from other rocks. The rock cycle is the repeated series of
events by which rock gradually and continually changes from one type to another.
“WORDY VERSION” OF ROCK CYCLE
Magma (hot, molten rock) beneath the earth’s surface is the source of all rocks.
Once magma reaches the surface (lava), or cools in the interior (as magma) igneous rocks are formed.
Once igneous rocks are weathered and erodedsedimentary rocks are formed.
Sedimentary rocks (and sometimes igneous rocks) are buried and caught in Earth’s movementsmetamorphic rocks are fomed.
“SCHEMATIC” ROCK CYCLE
“VISUAL” ROCK CYCLE
MAGMA Is hot, molten rock beneath Earth’s surface Is called lava once it reaches the surface Four types:
Felsic
Intermediate
Mafic
Ultramafic
FELSIC MAGMA Thick and slow moving Large amounts of silica Hardens into rocks of light-colored silicate
minerals
MAFIC MAGMA Hotter, thinner than felsic Large amounts of iron and magnesium Forms rocks of darker colors
INTERMEDIATE MAGMA Mix between felsic and mafic
Ultramafic Low Si High Fe and Mg Green in color or
green tint Varying densities Kimberlites are rare
ultramafic rocks where diamonds have been found in Kimberly, S Africa
Peridotite
Dunite
IGNEOUS ROCKS
Although all igneous rocks form from magma, they are not all the same.
The differences are caused by: Variations in the magma’s composition Variations in the formation process
Formed from underground magma intrusive Formed at Earth’s surface extrusive
TEXTURE OF IGNEOUS ROCKS
The texture of an igneous rock is caused by the rate of cooling. Cools rapidly extrusive glassy, fine-grained
texture Cools slowly intrusive coarse texture, crystals
formed
Igneous Textures Fine Grained- cools fast,
small crystals form (too small to be seen without the use of a microscope)
Coarse Grained- cools slowly, large visible crystals (easily seen with the eye, many colors or patterns)
Basalt
Granite
Igneous Textures Glassy: cools too fast for
crystals to form.
Porphyritic: mixture of fine and coarse grains. Fine grained ground mass with large crystals mixed in.
Pumice Obsidian
Andesite
Bowen’s Reaction Series A Canadian
scientist, N.L. Bowen, demonstrated that as magma cools, minerals form in predictable patterns.
Each mineral crystallizes at a different temperature.
SEE “Explore” of your Discovery Techbook, Igneous Rocks
FAMILIES OF IGNEOUS ROCKS
Are grouped together based solely on mineral composition, so a family can have rocks of all different textures and origins.
Three main families: Granite Family Gabbro Family Diorite Family
GRANITE FAMILY Form from felsic magmas Usually coarse-grained from slow cooling Usually made of quartz, feldspar, mica, and
hornblende Granite Obsidian Pumice Rhyolite
GRANITE
OBSIDIAN
PUMICE
GABBRO FAMILY Mainly made from mafic magma Darker in color and denser than granite
family Gabbro Basalt Scoria
GABBRO
BASALT
SCORIA
DIORITE FAMILY From intermediate magma (characteristics
of felsic and mafic) Color is darker than granites and lighter
than gabbros (dark greys and greens) Diorite andesite
IGNEOUS INTRUSIONS Are rock masses that form when magma
cools inside Earth’s interior Forces within the earth push magma up
into the bedrock Igneous intrusions are also called plutons
TYPES OF IGNEOUS INTRUSIONS
Dikes—sheet of igneous rock cuts across rock layers vertically or at a steep angle
Sills—sheet of igneous rock that lies parallel to the layers it intrudes
Laccoliths—from stiff magma that does not flow easily—bulges upward to form domed masses
Batholiths—form core of mountain ranges (largest of all intrusions)
SEDIMENTARY ROCKS While most of the earth’s crust is made of
igneous rock, most of the earth’s surface is made of sedimentary rock
Formed from the compaction and cementation of layers of sediments
FAMILIES OF SEDIMENTARY ROCKS
Are grouped according to their formation process
Three general groups in text: Clastic Chemical Organic
CLASTIC ROCKS Are formed from the fragments of other
rocks Conglomerates—the coarsest clastic rocks Sandstones—made of quartz and sand Shales—made of silt and clay
CHEMICAL ROCKS Made when minerals precipitate out of a
solution Rock salt Rock gypsum Some limestones
ORGANIC ROCKS Form from sediments of plant or animal
remains Limestone Coal
FEATURES OF SEDIMENTARY ROCKS
Stratification Fossils Ripple marks Mud Cracks Nodules Concretions geodes
STRATIFICATION The arrangement of visible layers Most apparent characteristic of sedimentary
rocks Line between layers is called bedding
plane Usually horizontal, but cross-bedding can occur
FOSSILS The remains, impression, or any other
evidence of a plant or animal preserved in rock
RIPPLE MARKS Sand patterns formed by the action of
winds, streams, waves, or currents
MUD CRACKS Occurs where a muddy road or puddle of
water has dried out after the rain
Modern Ancient
NODULES Hard lumps of silica in limestone and chalk
CONCRETIONS Round, solid masses of calcium carbonate
in layers of shale
GEODES Spheres of rocks filled with crystals that
occur in limestones
METAMORPHIC ROCKS Formed by the effect of heat and pressure
on other rocks Formed from pre-existing rocks called
parent rocks Usually resemble their parent rocks
METAMORPHISM Process by which a rock’s structure is
changed by heat, pressure, and moisture Two Basic Types:
Regional Local
REGIONAL METAMORPHISM Occurs in large areas Forms most of the metamorphic rock of
Earth’s crust Can occur during mountain-building
process
LOCAL METAMORPHISM Occurs in smaller, distinct areas Two Types:
Contact hot magma moves into rock, heating and changing it (can even change mineral compostion)
Deformational occurs at lower temperatures and is more due to pressure (composition does not change but deforms shape and texture)
CLASSIFICATION OF METAMORPHIC ROCKS
Based on a variety of properties: Parent rock Mineral content Texture Foliation—tendency to form bands of minerals or
split along parallel layers
CLASSIFICATION OF METAMORPHIC ROCKS
Metamorphic Rocks are also classified by their “grade” or degree of metamorphism:
Even the minerals in a
rock can change with
metamorphism (but not always!)
EXAMPLES OF METAMORPHIC ROCK
Quartzite a metamorphosed sandstone Marble a metamorphosed limestone Slate, phyllite, schist metamorphosed
shales Gneiss—most highly metamorphosed
from a variety of parent rocks
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