Page 131 - Laboratory Manual in Physical Geology

ACTIVITY naturally cemented together. They also form when
mineral crystals precipitate from water to form a rocky
4.1 Rock Inquiry mass such as rock salt or cave stalactites.
■ Metamorphic rocks are rocks deformed or changed
THINK What are rocks made of, and where and from one form to another (transformed) by intense
About It how do they form? heat, intense pressure, and/or the action of hot fluids.
This causes the rock to recrystallize, fracture, change

OBJECTIVE Analyze rock samples and infer where color, and/or flow. As the rock flows, the flat layers are
and how they formed? folded and the mineral crystals are aligned like parallel
needles or scales.
PROCEDURES
1. Before you begin , do not look up defi nitions and
information. Use your current knowledge, and
complete the worksheet with your current level of The Rock Cycle
ability. Also, this is what you will need to do the All rocks are part of a system of rock-forming processes,
activity: materials, and products that is often portrayed in a
____ pencil(s) with eraser conceptual model called the rock cycle ( FIGURE 4.2 ).
____ Activity 4.1 Worksheet (p. 121 ) The rock cycle model explains how all rocks can be
2. Analyze both rocks, and complete the formed, deformed, transformed, melted, and reformed
worksheet in a way that makes sense to you. as a result of environmental factors and natural processes
that affect them.
3. After you complete the worksheet , read about
rocks and the rock cycle below and be prepared
Igneous Processes. An idealized path (broad purple

to discuss your observations, interpretations, and
arrows) of rock cycling and redistribution of matter is
inferences with others.

illustrated in FIGURE 4.2 , starting with igneous processes.

If magma (from the mantle or lower crust) cools, then
it solidifies into igneous rocks that are masses of glass or
aggregates of intergrown mineral crystals.
Rocks and the Rock Cycle Sedimentary Processes. If these igneous rocks are

Most rocks are solid aggregates of mineral grains (par- uplifted, then sedimentary processes force other changes
ticles), either mineral crystals or clasts (broken pieces) to occur. The igneous rocks are weathered (fragmented
of mineral crystals and rocks (e.g., pebbles, gravel, sand, into grains, chemically decayed to residues, or even
and silt). There are, however, a few notable rocks that dissolved), eroded (worn away) and transported
are not made of mineral grains. For example, obsidian is (moved to a new place), and later deposited to form
a rock made of volcanic glass, and coal is a rock made of sediment (an accumulation of chemical residues and
plant fragments. fragmented rocks, mineral crystals, plants, or animals).
Meteorites (dust and rocks from space) may be
Three Main Groups of Rocks incorporated into the sediment. Sediment is lithified
(hardened) into sedimentary rock as it compacts under
Rock-forming materials come from Earth’s mantle
its own weight or gets naturally cemented with crystals
(as molten rock called magma while underground and
precipitated from water.
lava when it erupts to the surface), space (meteorites),
organisms (parts of plants and animals), or the

fragmentation and chemical decay of mineral crystals and Metamorphic Processes. If the sedimentary rock is
other rocks. Environmental changes and processes affect subjected to metamorphic processes (intense heat, intense
these materials and existing rocks in ways that produce pressure, or the chemical action of hot fluids), then it will
three main rock groups ( FIGURE 4.1 ): deform (fold, fracture, or otherwise change its shape) and
transform (change color, density, composition, and/or
■ Igneous rocks form when magma or lava cool general form) to metamorphic rock. And if the heat is great
to a solid form—either glass or masses of tightly enough, then the metamorphic rock will melt (an igneous
intergrown mineral crystals. The crystals are large process) to form another body of magma that will begin the
if they had a long time to grow in a slowly cooling cycle again.
magma, and they are small if they formed quickly in
a rapidly cooling lava.
Multiple Pathways Through the Rock Cycle. Of
■ Sedimentary rocks form mostly when mineral course, not all rocks undergo change along such an
crystals and clasts (broken pieces, fragments) of plants, idealistic path. There are at least three changes that
animals, mineral crystals, or rocks are compressed or each rock could undergo. The arrows in FIGURE 4.2

112 ■ L ABOR ATORY 4