Rocks S6E5 Students will investigate the scientific view of how Earths surface is formed. b.Investigate the composition of rocks in terms of minerals.

RocksS6E5 Students will investigate the scientific view of how Earth’s surface is formed.b.Investigate the composition of rocks in terms of minerals.c.Classify rocks by their process of formation

S6E5 Students will investigate the scientific view of how Earth’s surface is formed.Investigate the composition of rocks in terms of minerals.Classify rocks by their process of formation

Earth’s crust is made of rock.

Rocks are made of mixtures of minerals and other materials, although some rocks may contain only a single mineral.

Mineral mixturesGranite is made up of the minerals quartz, feldspar, mica, andhornblende, and sometimes other minerals.

When studying a rock sample, geologists observe the rock’s color and texture and determine its mineral composition. These characteristics are used to determine a rock’s origin.

Texture-the size, shape and pattern of the rock’s grains

Mineral composition- Rocks are viewed under a microscope to determine their mineral composition.

Fine-grained

slate

No visible grain

Flint

Coarse-grained

Jagged grain

Rounded grain

•

Origin – There are three major groups of rocks: igneous, sedimentary, and metamorphic.These terms refer to how the rocks in each group formed. Key Ideas:A rock is a hard piece of Earth’s crust.Geologists classify rocks by their color, texture, mineral composition, and origin.The three types of rock classified by origin are igneous, sedimentary, and metamorphic.

Igneous RockIgneous rock forms from the cooling of molten rock. The molten rock can be magma below the surface or lava at the surface.

How Magma Forms• A rise in temperature can cause the minerals

in a rock to melt. Different minerals have different melting points.

• A change in composition – When fluids enter a rock, it can change the composition and lower the melting point.

• A release of pressure – At very high pressure, a rock will remain solid. If pressure is released, it will melt.

Igneous rocks are classified according to their origin, texture, and mineral composition.

Origin- extrusive or intrusiveExtrusive igneous rock formed from lava that erupted onto Earth’s surface.Basalt is the most common extrusive rock. Basalt forms much of the crust, including the crust beneath the ocean floor.

Intrusive igneous rock is formed when magma hardens beneath Earth’s surface.Granite is the most abundant intrusive igneous rock that makes up the continents. Granite forms the core of many mountain ranges.

Igneous rocks are classified by origin, texture, and mineral composition. (continued)

Texture – The texture of an igneous rock depends on the size and shape of the mineral crystals. Rapid cooling lava forms fine-grained igneous rock.(extrusive) Slow cooling lava forms course-grained igneous rock.(intrusive)

Rhyolite is a fine-grained igneous rock with a mineral composition similar to granite.

Pegmatite is a very coarse-grained variety of granite.

A rock with large crystals scattered on a background of much smaller crystals has a porphyritic texture. Porphyritic rocks form when intrusive rocks cool in two stages. As the magma begins to cool, large crystals form slowly.As magma moves closer to the surface, the remaining magma cools more quickly, forming smaller crystals.

Porphyry has large crystalssurrounded by fine-grained crystals.

Mineral composition – Most of Earth’s minerals contain silica- a material formed from oxygen and silica. The silica content of magma and lava affects the types of rocks they form.

Mafic- low silica rocks (more dense)Mafic rocks have a higher content of calcium, iron, and magnesium. Mafic rocks are darker in color.

Felsic- high silica content , as well as aluminum and potassium, (less dense)Felsic rocks are light in color.

BasaltGabbro

Rhyolite

Granite

Uses of Igneous Rock

Granite has a long history as a building material.

Pumice is a good abrasive for cleaning.

Basalt is crushed to make gravel.

Igneous Intrusive Bodies• Masses of intrusive igneous rock are named

for their size and shape• A batholith is the largest igneous intrusion.

Dikes are formed when magma cuts across layers.

Sills are formed when magma squeezes between layers of rock.

Stone Mountain is a batholith.

Key PointsIgneous rocks form from magma or lava. Igneous rocks are classified according to their origin, texture, and composition.

Extrusive igneous rocks are fine-grained.Intrusive igneous rocks are coarse-grained.

Mafic igneous rocks are dark-colored due to a low silica content.

Felsic igneous rocks are light-colored due to a high silica content.

Identify these rocks as mafic or felsic.

• Granite

Rhyolite

Basalt

Gabbro

Use the scientific method to rate your rocks from least dense to most dense.

• On a sheet of paper to turn in write:• Question: How do these rocks rate in order of most

dense to least dense?• Gather information: What do you know about these

rocks?• Write your hypothesis: Predict the density of your

rocks from least to greatest.• Experiment: Use the data sheet to determine

density.• Record and analyze data• State your conclusion