Rocks & minerals  Lake Superior Agates  To be able to "read" the
stories rocks tell us, we first need to know what rocks and
minerals are.   Minerals are naturally occurring chemicals, or
combinations of chemicals. Minerals are not formed by living
things, so they are called inorganic. There are over 3,500 known
minerals in the world today!   Rocks are made of minerals. They
can be made of a single mineral or a combination of several
minerals.  Igneous rocksThere are three main types of rocks:  1)
Igneous (IG-nee-us) rocks are formed from hot, molten rock,
called magma. Granite and basalt are examples of igneous rocks.
Sedimentary rocks2) Sedimentary rocks are formed from bits and
pieces of rock which have broken off. These bits and pieces are
called sediments. The sediments were carried by water and wind
and dropped to a new location. The sediments are piled layer
upon layer and pressed or cemented together to form a new kind
of rock. The most common sedimentary rocks are sandstone,
limestone, shale, and co