Lava is a pretty cool type of rock that almost everybody loves. Molten rock, as it is also known, since the rock is so heated up that it turns to the liquid form, can end up in different textures and different consistencies as it cools. As you can see by the pictures we have two very different looking rocks. One looks sharp, ridged, and would hurt if you walked on in bare feet (see below). This type of lava rock is called Aa (pronounced ah-ah), somewhat like the sound you would make if you were to walk on it with bare feet. The other picture shows an example of the other type of lava rock. This one is called Pahoehoe (pronounced puh-hoy-hoy). It is more smooth and ropey looking. According to this picture it would also hurt to stand on it with bare feet because it is still hot. The consistancy of lava rock is often basalt but can be classified as other types.
One may ask why these two different types of lava rock form. There can be several factors that influence why they form differently, but the main principle is the viscosity of the magma. Viscosity is defined as "the resistance to flow." If something has a high viscosity, it has a high resistance to flow, such as cold honey. Cold honey is lumpy and difficult to get out of the bottle. Low viscosity or a low resistance to flow would be like honey that has been heated up and runs easily out of the bottle. Some factors that affect viscosity is the temperature of a material and the amount of water in a material.