Chapter 3 - Rocks
January 2013
3-1 What are rocks?
• Rocks in Earth’s Crust
1. Petrologists study rocks & minerals.
2. Rocks are made of minerals (2000).
• Classification of Rocks
1. Classification is the grouping of things that are alike.
2. Petrologists classify rocks & minerals.
• Classes of Rocks
1. Petrologists classify rocks by the way they form.
2. The THREE classes of rocks are: igneous, sedimentary,
and metamorphic.
Section 3-2 How are igneous rocks formed?
• Heat Inside Earth
1. The deeper you dig, the hotter it gets
2. Molten rock is made of melted minerals.
• Magma and Igneous Rock
1. When molten rock cools and hardens, igneous
rock is formed.
2. Igneous rock can take thousands of years to form
from magma inside Earth.
• Lava and Igneous Rock
1. Igneous rocks form quickly from lava above
Earth’s crust.
Section 3-3 How are igneous rocks classified?
• A Combination of Minerals
1. The SIX most common minerals in igneous rocks are
Quartz, Mica, Amphibole, Feldspar, Olivine, & Pyroxene
• Crystal Size
1. Crystal size depends on the amount of time it takes the
molten rock to cool.
2. Magma = large crystals; Lava = small or none
• Texture
1. Texture can be used to identify rocks.
2. Large crystals are coarse; small crystals are fine; no
crystals are glassy
3-4 How are sedimentary rocks formed?
• Sediments
1. The heaviest sediment sinks first.
• Natural Cement
1. As more layers form, water is squeezed out.
2. Dissolved minerals act as cement.
• Sedimentary Rock From Living Things
1. Rock can be formed from the remains of living
3-5 Classifying Sedimentary rocks
• Groups of Sedimentary Rocks
1. Clastic rocks are made from rock particles.
2. Nonclastic rocks are made from dissolved
minerals or the remains of living things.
• Particle Size
1. Sandstone and Shale are clastic rocks
• Dissolved Minerals
1. Limestone and halite are nonclastic rocks.
• Plants and Animals
1. Coals are nonclastic rocks formed from the
remains of plants.
3-6 How are metamorphic rocks formed?
• Changed Rocks
1. Heat & pressure inside Earth change rocks over
• Heat and Pressure
1. Too much heat will melt a rock or mineral.
2. Extreme pressure will cause flattening (layers).
• Magma
1. All rock types can be changed into metamorphic
3-7 How are metamorphic rocks classified?
• Classifying Metamorphic Rocks
1. Metamorphic Rocks can be foliated or nonfoliated
depending on their mineral crystal bands.
• Banded Metamorphic Rocks
1. Foliated rocks have crystals arranged in bands.
2. Gniess (from granite) and schist (from shale) are
examples of foliated rocks.
• Metamorphic Rocks Without Bands
1. Nonfoliated do not have minerals arranged in bands.
2. Quartzite is an example (from sandstone).

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