STUDY GUIDE: ROCKS
Section 5-1: CLASSIFYING ROCKS
When studying rocks, geologists observe the following characteristics of rocks
a. Mineral composition
b. Color
c. Texture
Rocks are classified into three major groups:
1) Igneous Rock: forms from the cooling of magma or lava
Examples: Granite, Basalt, Obsidian
2) Sedimentary Rock: forms when particles of other rocks or the remains of
plants and animals are pressed and cemented together
Examples: Limestone, Sandstone, Shale
3) Metamorphic Rock: forms when an existing rock is changed by heat,
pressure or chemical reactions
Examples: Slate, Marble, Gneiss
Section 5-2: IGNEOUS ROCKS
IGNEOUS ROCKS: classified according to: origin, texture, and mineral composition
Origin:
Extrusive Rock: formed from lava that erupted onto Earth’s surface
BASALT- most common extrusive igneous rock; oceanic crust forms from the
rapid cooling of lava to form basalt
Intrusive Rock: formed when magma hardens beneath Earth’s surface
GRANITE: most abundant intrusive rock in the continental crust
Texture:
o Rapid cooling lava forms fine-grained igneous rocks with small
crystals
o Slow cooling magma forms course-grained rocks with large crystals
o Rock that is cooled very rapidly can form without crystals resulting in a
smooth, shiny texture
Section 5-3: SEDIMENTARY ROCKS
SEDIMENT: small, solid pieces of material that come from rocks or living things
Most sedimentary rocks are formed through a series of processes:
a) Erosion: running water, wind, or ice loosen and carry away fragments of
rock
b) Deposition: the process by which sediment settles out of the water or wind
carrying it
c) Compaction: the process that presses sediments together
d) Cementation: the process in which dissolved minerals crystallize and glue
particles of sediment together
EROSION  DEPOSITION  COMPACTION  CEMENTATION
(See Figure 9 on page 153 in Inside Earth for a picture of how sedimentary rock
forms)
Types of Sedimentary Rock:
1) Clastic Rocks- sedimentary rock that forms when rock fragments are
squeezed together
2) Organic Rocks- forms where the remains of plants and animals are deposited
in thick layers
3) Chemical Rocks- form when minerals dissolved in a solution crystallize
Section 5-5: METAMORPHIC ROCKS

Heat and pressure deep beneath Earth’s surface can change any rock into
metamorphic rock.
**Look at the chart on page 165 in the text (The Rock Cycle). Mr. Walker also gave
you a copy of this chart. You don’t need to memorize this chart, but you do need to
be able to look at it and say what’s going on in the Rock Cycle while looking at it.