METAMORPHIC ROCKMetamorphic rocks are what you might call ‘cooked rocks,’ in that they are existing igneous, sedimentary or older metamorphic rocks that are transformed by heat, pressure and chemical processes. The source rock or prolith may be subjected to heat greater than 150°C and pressure above 1500 bars beneath the earth’s surface. Metamorphic rock may also form from tectonic processes such as plate collisions which create horizontal pressure, friction and distortion. Metamorphic rock can also form when rock is heated by an intrusion of magma from earth’s interior (migmatization). The process of metamorphic rock formation is called metamorphism.

Composition of Metamorphic Rocks

As you might expect, metamorphic minerals are formed during the high temperatures and pressures that are associated with metamorphism. These mierals include kyanite, sturolite, gamet, andalusite and sillimanite. These minerals are known as index minerals in metamorphic rock formation. when index minerals are found on a metamorphic rock, it indicates the minimum pressure and temperature the prolith must have experienced during its formation. The higher the pressure, the higher the grade of rock.

Other minerals in metamorphic rocks include olivine, pyroxene, mica, feldspars and quartz which may not form during the process of metamorphism.

Classification of Metamorphic Rocks

One aspect of many metamorphic rocks that sets them apart from igneous and sedimentary rock is their foliated or layered appearance. The term foliation comes to us from the Latin folia meaning ‘leaves.’ Metamorphic rocks are classified by their foliation- or lack of it. Non-foliated rocks include marble (shown right above), while foliated metamorphic rocks include slate, hornfel (shown to the right below) and gneiss.

Formation of Metamorphic Rock

As an example, let’s learn about the formation of mudstone and shale into the metamorphic rock slate. Slate typically forms in former sedimentary basins that become associated with a convergent plate boundary. the mudstone and shale are compressed by horizontal forces and minor heating, which heat and modify the clay minerals in those rocks as shown in the illustration to the left.

Foliation then develops at right angles in response to the compresive forces of the convergent plate boundary. This yields a vertical foliation that typically crosses the bedding planes that previously existed in the shale as shown in the image below. The foliation in slate allows it to break apart into thinner sheets which make it handy for home construction projects among other things.

FEATURED PINTEREST PINS

https://www.pinterest.com/hgoconor/geology/Harvey O’Coner’s Geology Website is a great collection of all things geological that you might find handy in your study of rocks and minerals.

https://www.pinterest.com/pin/385268943099341258/A great illustration showing the boundary between Permian and Triassic rock formations.

https://www.pinterest.com/pin/236931630371481475/Another image of metamorphic rock layers with a description of their formation.

https://www.pinterest.com/pin/157485318196133068/Nice image of Devonian metamorphic rocks- more specifically garnet-bearing gneiss.

https://www.pinterest.com/pin/317363104967682725/Nice illustration highlighting the difference between contact and regional metamorphism

https://www.pinterest.com/pin/32510428532628600/A great illustration and description of gneiss.

https://www.pinterest.com/pin/36380709460129793/Using cake to teach about metamorphic rock.

https://www.pinterest.com/pin/388576274081740078/Nice illustration of metamorphic rock formation.

RECOMMENDED INTERNET RESOURCES

http://www.onegeology.org/extra/kids/metamorphic.htmlOne geology Kids website that should provide a great introduction to metamorphic rocks for younger students.

http://www.tulane.edu/~sanelson/eens212/metatexture.htmTulane University website with a great description of the foliation process.

http://geomaps.wr.usgs.gov/parks/rxmin/rock3.htmlUSGS webpage describing metamorphic rocks.

http://maps.unomaha.edu/maher/geo117/117metamorph.htmlUniversity of Nebraska webpage describing metamorphic rock formation.

http://www.uno.edu/cos/earth-environmental-sciences/resources-docs/l05_metamorphic_rocks.pdfNice PDF describing metamorphic rock processes.

http://www.geosci.ipfw.edu/PhysSys/Unit_4/metam.htmlA great all-purpose page describing most aspects of metamorphic rocks.

http://www.rocksandminerals4u.com/metamorphic_rocks.htmlRocks and Minerals for You Web Page describing metamorphic rocks and their formation.

http://geology.com/rocks/metamorphic-rocks.shtmlGeology.com website with lots of great images of metamorphic rocks.

https://www.youtube.com/watch?v=1oQ1J0w3x0oMichael Sammartano video describing metamorphic rock formation.Includes a downloadable worksheet that you can do with the video. Graphics minimal but effective.

https://www.youtube.com/watch?v=YBLOcdTC7DAAnother great video describing metamorphic rock formation.

https://www.youtube.com/watch?v=ckypDmkbhb8Nice video that should help you learn how to identify metamorphic rocks.

https://www.youtube.com/watch?v=HUydPhIaQQUAnother great video on metamorphic rock formation that emphasizes mineral content of the rocks.

https://www.youtube.com/watch?v=Ncr-46YX-N0Another good all-purpose video about metamorphic rocks.

http://www.slideshare.net/cfoltz/earth-science-24-metamorphic-rockSlideshare presentation of metamorphic rock formation.

http://www.slideshare.net/md5358dm/metamorphism-and-metamorphic-rocks-pptNice detailed description of metamorphic rocks and their formation.

http://www.slideshare.net/anandjaydip/ref-book-kidsdkrocknmineralsAn excellent DK book presentation of rocks and minerals and their uses.

http://www.ck12.org/book/CK-12-Earth-Science-Concepts-For-High-School/section/3.16/Sample activity that may be a good training model for your team.

DOWNLOAD AN INTERACTIVE PDF OF THIS PIN AT WWW.VANHECKESCIENCE.COM

Mark A. Van HeckeInstructional Design Consultantwww.vanheckescience.commvanhecke@comcast.net