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
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
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.