This is always the case in a decomposition reaction. Don't forget that!! Figuring out what the products are in decomposition is harder (maybe you'll think it's easier!!) because you will have to recognize several categories of decomposition reactions.
Geology. a small, usually spherical cavity in a rock or mineral, formed by expansion of a gas or vapor before the enclosing body solidified. Origin of vesicle.
Vesicles are air bubbles that form in extrusive igneous rock. What sub-type of igneous rock contains vesicles and why does it contain them? Vesicles are commonly found in extrusive igneous rock because of gases that form from lava as the material solidifies -- like bubbles in a bottle of soda when you open it.