Looking at its creation, metamorphic rocks are previous sedimentary and igneous rocks that underwent different chemical changes which resulted in a new rock form. “Metamorphic rocks are formed when other kinds of rocks are changed by great heat and pressure inside the earth” (Koday, 1998). Seeing such development, different outcomes are formed depending on the amount of heat and pressure exerted on a particular igneous or sedimentary rock form to create a different type with varied textures. (How Rocks are Created, 1997)
Rock formation towards a metamorphic state requires two factors for it to form – temperature and pressure. “When igneous, sedimentary or even metamorphic rocks get buried deep beneath the surface of the earth, over millions of years the heat and pressure inside the earth change them into something else” (Koday, 1998). One way to determine the composition of a metamorphic rock is looking at its texture. “Texture, structure, and mineral content of metamorphic rock depend both on its protolith (parent material) and metamorphic conditions” (Cochran, 1999).
Seeing this, there are two categories of metamorphic rocks namely (1) foliated and (2) non-foilated. Looking at such categorization, there are different ways and characteristics to distinguish the differences between the two. Looking at a foliated metamorphic rock, its main characteristic is that it is arranged and aligned to showcase its development into such state. Thus, it can be argued that these rocks are low grade and underwent high heat and pressure.
On the other hand, for non-foilated rocks it is different. Contrary to foliated metamorphic rocks, non-foilated rocks have no distinct pattern and tend to showcase crystal-like appearance. As far as the catalyst factors are concerned, non-foilated rocks underwent little or moderate pressure for it to form. Also these rocks tend to have higher grade and harder than foliated types.
References
Cochran, C. (n.d.) Metamorphic Rocks. Retrieved July 2, 2008 from
http://home.att.net/~cochrans/metrok01.htm
Koday (1998) Metamorphic Rocks. Retrieved July 2, 2008 from
http://www.ivyhall.district96.k12.il.us/4th/KKhp/RocksandMinerals/metamorphic.html
How Rocks are Created (1997) How Metamorphic Rocks are Formed. Retrieved July 2, 2008
from http://www.fi.edu/fellows/payton/rocks/create/metamorph.htm
