There are many different types of igneous rocks. However, they all were
once melted and have since cooled down. Igneous rocks look different because
of two factors: (1) they are cooled at different rates and (2) the
"Mother" Magma (original melted rock)was different. These two
factors create many different types of igneous rocks.
Sedimentary rocks are formed in 2 major ways: (1) clastic material
(pieces of other rocks or fragments of skeletons) cemented together, and (2)
chemical means (usually precipitation). Usually sedimentary rocks are
associated with water (erosion, settling, and cemented together). However,
other sedimentary environments include wind erosion, and glacial movement.
Metamorphic rocks were either igneous, sedimentary, or other metamorphic
rocks that were changed. They were changed by great pressures and
temperatures inside the earth. The temperatures were not enough to melt the
rock, otherwise it would be igneous. The pressures were not enough to break
the rock, otherwise it would be sedimentary. The conditions were just enough
to change the chemical make up of the rock by forcing the elements to
Introduce the terms igneous rocks, sedimentary rocks,
and metamorphic rocks.. Concentrate especially on the environments of each
type of rock. Explain that igneous rocks are "hot" rocks;
sedimentary rocks are "cool or wet" rocks; and metamorphic rocks
are "changed" rocks.