Vermiculite is an alumino-silicate clay processed by heating to make it expand; it draws nutrients by soaking up water while perlite is volcanic rock, rich in silicon, which absorbs less water but aerates soil more efficiently. The two substances serve in different capacities in the potting of houseplants and flowers.
Vermiculite can absorb three to four times its own weight in water. In this way, it absorbs nutrients and substances like potassium, magnesium and calcium both from the soil and from the water in it and holds them close to the roots of any plants it nourishes. For some plants, this can prove lethal as heavy saturation can cause rot, but others require that degree of exposure.
Perlite aerates soil, meaning it can be used to pot plants with a need for dry environments. It greatly improves the drainage in most potted plants, necessitating a receptacle for the excess water. While it does not trap nutrients as well as vermiculite, it does to some degree trap water in the same manner.
While the two substances are distinct from one another, they do share a handful of qualities. These include absorption and utility in potting. Their differences include the composition of the minerals involved, the rate of absorption of groundwater, and the types of minerals absorbed.