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There
are three basic kind of rocks found in the surface of the Earth:
igneous, sedimentary,
and metamorphic.
Igneous rock is formed by the cooling and solidification of molten
(melted) rock material. Basalt
is found in great quantities in this area and can be identified
by its plain dark gray or black color. Find the basalt sample
in the display case. Other igneous rocks include rhyolite,
obsidian, scoria and pumice.
Sedimentary rock form from material deposited by water, wind or
ice. In this tour we will see examples of sedimentary rock in
the form of sandstone, limestone,
and shale. Sandstone is made
of sand-sized particles and has the texture of sandpaper. Shale,
also called mudstone, is made of smaller sized particles of clay.
Limestone may form from sea shells at the ocean floor.
Metamorphic rock forms through the alteration of preexisting rocks
by heat and pressure. Meta means change, morph refers to structure.
Limestone metamorphoses to marble,
sandstone to quartzite, shale to slate, and granite to gneiss.
Have you learned about anything else that goes through metamorphosis?*
We will see examples of the three kinds of rocks along our tour.
Come back to this exhibit to learn more about the fossil record
of Oregon.
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