BACKGROUND:
In order for the students to understand igneous rocks,
they will need to know two factors that influence what type of rocks a
volcano will produce. First, the manner in which lava cools will determine
many different aspects of the igneous rock that will be produced. Second,
the original chemical composition of the parent magma will play an important
role in the formation of the igneous rock. It determines the mineral content
of the rock. Remember, minerals make up rocks.
PROCEDURE:
- Hold up different kinds of igneous rocks for the students to examine.
Be sure to use a slow cooled rock (granite) and one or more fast cooling
ones (any of the other samples). Ask the students which rock cooled
inside the Earth. They should answer granite. Ask them whether the
melted rock or magma (inside the crust), produced different rocks. They
should answer yes, because the granite looks different, especially in
mineral content.
- Show the students the rock samples that they examined in in the lab.
Instruct students to predict which one of the three rocks cooled
the fastest. The pumice and obsidian cooled before the basalt. Ask them
how they know. The basalt has tiny mineral crystals, the pumice and
obsidian do not. Remember that the quicker a lava flow cools the less
time there is for minerals to form.
- Volcanoes are very interesting to students. You may want to have the
books or other resources available for students to obtain more
information. Here is a recommended website:
http://www.geo.mtu.edu/volcanoes/
University of Michigan volcano sites around the world.
- Have the students complete the worksheet. It may also be used as a
test.
Answers: (1) lava; (2) magma; (3) volcano; (4) obsidian; (5)
pumice; (6) Hawaii; (7) Mt. St. Helens; (8) granite; (9) basalt; (10)
ash
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