Foliated:

Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned. These rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied in. Slate, schist, and gneiss (pronounced 'nice') are all foliated metamorphic rocks.

Non-Foliated:

Non-foliated metamorphic rocks do not have a platy or sheet-like structure. There are several ways that non-foliated rocks can be produced. Some rocks, such as limestone are made of minerals that are not flat or elongate. No matter how much pressure you apply, the grains will not align! Another type of metamorphism, contact metamorphism, occurs when hot igneous rock intrudes into some pre-existing rock. The pre-existing rock is essentially baked by the heat, changing the mineral structure of the rock without addition of pressure.

Typical Rocks: pegamatites, serpentinite, soapstone

Hydrothermal metamorphism occurs when hot, chemically active, mineral laden waters interact with a surrounding preexisting rock (called the country rock). Most hydrothermal metamorphism takes place at low pressures and relatively low temperature. It is one of the most pervasive and widespread types of metamorphism, although most of it cannot be seen easily. There are also several distinctly different types of hydrothermal metamorphism:

• Igneous Fluids and Pegmatite's: The most spectacular hydrothermal metamorphism takes place as an after effect of igneous activity. Magmas have lots of water with dissolved minerals, but as the magma crystallizes the mineral laden water is driven off into the surrounding country rock where it seeps into cracks and pores precipitating the minerals.
  The most spectacular result of this is a pegmatite, a very coarse grained felsic igneous rock. Pegmatite's commonly have single crystals measured in feet in size, as well as a host of exotic minerals, including some of the most important gem minerals.
  Hydrothermal deposits of this type also produce many important mineral deposits, from silver and gold to copper.
• Oceanic Hydrothermal Metamorphism: A second type of hydrothermal metamorphism takes place at oceanic rift centers (divergent plate boundaries). Here magma oozes out onto the ocean floor to form pillow basalt's. While the rock is still hot sea water carrying all its salts percolates into the rocks where a lot of chemical reactions take place. Minerals are leached out of the rock and carried to the surface where they often form smokers, geysers on the ocean floor
  

Typical Rocks: hornfels, quartzite, marble, skarn

Contact metamorphism occurs in the " country rock" (the rock intruded by and surrounding an igneous intrusion). Rocks are " baked" into a ceramic from heat escaping from intrusives, often enhanced by hydrothermal fluids. The intensity of metamorphism decreases with distance from the intrusion, until at some distance away the rock is unaltered country rock. The metamorphism often occurs in aureoles, or zones surrounding the intrusion. Close to the intrusion is the hydrothermal (or metasomatic) aureole where minerals from the hot fluids have their greatest effect. Further away is the thermal aureole where heat is the primary effect. The dimensions of the aureoles are dependent on the size of the intrusive body and the amount of water present. In the absence of fluids, the aureole is very small. The assemblage of new minerals that grow in the country rock depend on the composition of the country rock. For a complex sedimentary parent of sandstones and shale's, anhydrous (without water) minerals such as garnet and pyroxene occur closest to the intrusion, then hydrous (water rich) minerals such as amphibole and epidote, and at the lowest intensity, chlorite and serpentinite occur.
When an magma intrudes into carbonates such as limestone and dolostone the carbonate reacts with silica from the hydrothermal fluids to form skarn. Many special lime-bearing silicate minerals form here.

Typical Rocks: eclogite

Eclogite metamorphism takes place in the mantle. The parent rock is ultramafic mantle material, such as peridotite. Eclogite is characterized by a pale green sodic pyroxene (omphacite) and a red garnet (almandine-pyrope), making it a striking rock. Associated minerals are rutile, kyanite, and quartz, and it is not unusual to have retrograde amphibole in the rock too. Since eclogite forms so deep, outcrops are not common.