The Earth has melted rock deep inside it.  This is called magma.  If the magma stays underground, cools, and hardens, it is called intrusive igneous rock.  Because it is inside the Earth, it cools slowly so that it makes big crystals. When the magma flows through and around other rocks, it makes veins of rock inside it.
     Extrusive igneous rock is made when magma comes to the Earth’s surface in the form of lava and then cools and hardens.  Lava flows out of volcanoes.  Lava and magma are the same.  They just change the name of the magma when it comes to the surface.  Since it cools quicker, the crystals of surface igneous rock are smaller.
     Some igneous rock is coarse or large grained and some is fine grained.  The kinds of minerals in the rock decide its color.  Silica makes the rock light colored and darker colors have other minerals and no silica in them.  Some usual combinations of minerals that make ores are lead-zinc, zinc-iron-manganese, or iron-titanium.  About 4/5ths of the Earth’s crust is made up of igneous rock.

Examples of igneous rocks:

• Gneiss

• Granite

• Sand

Examples of minerals found in igneous rocks: