Contact metamorphic rock is
rarer than the regional one.
It is the type that is hardest to recognize as a metamorphic
because it lacks foliation and schistosity.
These are the
rocks that have
formed close to igneous rocks - either
next to an ingeous intrusion, or lava flow.
The temperatures have been high enough that the rock has changed
without any help from changing pressures.
But they haven't been high enough for the rock to melt - if
it did, an
have formed. Those rocks include for example skarn
Skarn. By nile red via Flickr.com
calcite-rich rock that is formed by contact metamorphism of
limestone, often by syenite or granite
intrusions. Fluids of these
intrusions, in combination with limestone
impurities create a complex
mineralogy and skarn is known for many various minerals
tremolite, serpentine, diopside, wollastonite, periclase, olivine,
grossular garnet, and ore
as galena, sphalerite,
chalcopyrite and pyrite. Ore
deposits are often found in skarn.
Hornfels. By .RGB. via Flickr.com
forms by contact metamorphism close to igneous intrusions. It
can form from different parent rock and depending on the parent rock
and what minerals it has, there can be different hornfels, such as
garnet hornfels, pyroxene hornfels, chiastolite hornfels, cordierite
hornfels, and others. Generally they are known to be fine-grained,
sometimes porphyritic, and often quite hard to identify.