premise: if something usually happens then that something is likely to happen sent2: igneous rocks / minerals are formed by magma / lava cooling / crystallizing sent3: if something is formed by a material changing then that something is formed from that material sent4: a volcano is a source of magma / lava sent5: usually something can be found near a source in greater concentrations sent6: cooling is a kind of change sent7: lava is a kind of material sent8: pumice is a kind of igneous rock.
hypothesis: pumice is likely formed near a volcano