What is a magma ?

The ground on which we stand, the lofty mountains and the hidden floors of the sea form a rocky crust which wraps the globe in a sort of orange peal about 30 miles thick. The temperature of the earths crust is below the melting point of the elements, mixtures and compounds from which these rocks are made   which is why the crust is frozen solid.

In a few cracks and crevices deep in the crust, the temperature soars and the various minerals reach melting point. We get a pool of buried magma. The molten mixture may contain any other rocky minerals normally frozen solid on the surface. It may also seeth with foamy bubbles of gas and water vapor. In any case, the temperature of the magma is hot enough to melt rock.