Where do metamorphic rocks originate? How are they formed?
o What are the two categories of metamorphic rocks? What are the distinguishing
characteristics between the two categories of rocks?
Check these sites.
(Broken Link Removed)
http://library.thinkquest.org/J002289/meta.html
http://home.att.net/~cochrans/metrok01.htm
http://en.wikipedia.org/wiki/Metamorphic_rock
Metamorphic rocks originate from the transformation of pre-existing rocks under high temperatures and pressures deep within the Earth's crust. The process occurs when rocks are subjected to extreme heat and pressure, but without melting. This usually happens due to tectonic forces, such as plate collisions, and also from the heat generated by deep burial.
There are two categories of metamorphic rocks: foliated and non-foliated. The main distinguishing characteristic between these two categories is the presence or absence of a layered or banded appearance.
Foliated metamorphic rocks have a layered or banded appearance, resulting from the alignment of minerals in parallel planes or the presence of visible foliation. The alignment occurs due to pressure exerted on the rock during metamorphism. Examples of foliated metamorphic rocks include slate, schist, and gneiss.
Non-foliated metamorphic rocks, on the other hand, lack the layered or banded appearance. These rocks usually form from the recrystallization of minerals without significant pressure or shear stress. Non-foliated metamorphic rocks often have equidimensional or blocky grains. Examples include marble, quartzite, and hornfels.
To determine the category of a metamorphic rock, one can examine its texture, mineral composition, and the presence or absence of layered or banded structures. Using these distinguishing characteristics, it is possible to identify whether a metamorphic rock falls under the foliated or non-foliated category.