Rocks formed from magma in the Earth's mantle are called igneous rocks. However, there are different types of magma. Lava rocks can be basalt, andesite or rhyolite.
Basalt rocks form the Earth's crust. They are heavy, dark and grainy. The dark color of this type of rock comes from its high magnesium and iron content. Andesites have a lighter color compared to basalt because they contain more silica and less iron.
Rhyolites are light-colored or white. These rocks don't have much iron or magnesium; instead, they contain a lot of silica. Some rhyolitic rocks are very light because of the bubbles of gas that were trapped as they solidified.