Lava, Mist, Smoke, Mud

Para-Elemental Planes are created by the meeting of 2 Elemental Planes. Fire and Water, being diametrically opposed never connect, neither do Air and Earth. Though permanent portals exist to and from each of these Planes creating pockets of Para-Elemental Material unseen in the Outer Planes. The Elemental Planes do meet between Fire and Air, Air and Water, Water and Earth, and Earth and Fire.
Between Fire and Air is the Plane of Smoke, a realm of ashy, burnt sky.
Between Air and Water is the Plane of Mist, a wet vaporous expanse.
Between Water and Earth is the Plane of Mud, an ever-shifting mire.
Between Earth and Fire is the Plane of Lava, a constant flow of magma.
Where Fire and Water are allowed to come together creates the Para-Element: Steam.
Where Earth and Air are allowed to come together creates the Para-Element: Dust. Elementals from these Planes are rare, most often only gaining the size of a mephit or small elemental. Though wizards have long used these Para-Elemental Planes to draw spell components, energy, and raw materials, the study of Para-Elemental Planes has long been neglected.