THE ROCK CHRONICLES: Green Schist

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What is greenschist?

Greenschist is a fine-grained to medium-grained foliated metamorphic rock. It is dominated by chlorite (ClO2-), actinolite (Ca2(Mg,Fe)5Si8O22(OH)2), and epidote (Ca2(Al,Fe)2(SiO4)3(OH)). Greenschists form by regional metamorphism of mafic igneous rocks, usually basaltic rocks, under greenschist facies metamorphism. The name comes from commonly having an abundance of green minerals such as chlorite, serpentine, and epidote, and platy minerals such as muscovite and platy serpentine.





Figure 1. Unpolished green schist with visible sharp side.





Figure 2. Visible dull sides of an unpolished green schist.




Figure 3. Diamond-like polished green schist pictured with its sharp side visible.





Figure 4. Visible blunt edges of the polished green schist.




Specific Characteristics of Greenschist


Based on observation, the rock was sort of dusty and dull at first but after polishing it by washing it with water, the green color of the rock became more prominent. The rock’s texture is a mixture of smooth and rough sides. Since the rock is foliated, repetitive layering can be seen. Green schists are metamorphic rocks having shale, slate, phyllite, basalt, or granite as their parent rock thus it underwent metamorphism. Schists are often shiny due to the reflection of mica on foliation planes. However, this rock has only certain parts that are shiny. It also has sharp and dull edges.


Where can greenschists be found in the Philippines?


Greenschist is a general field petrologic term for metamorphic or altered mafic volcanic rock. Therefore, it can highly be found in regions where volcanoes are present. In the Southeast part of Bohol, greenschists are present. The Alicia Schist which appears to be Cretaceous, is the lowest formation in the region and consists of medium grade greenschist and mica schist.


Uses of Greenschist

Industrial:

Greenschist was used to pave floors of streets and courtyards between 1650 and 1600 BC. These rocks were likely quarried in Agia Pelagia on the north coast of central Crete. It is also used to make axes across Europe.Greenschists are also used as dimension stone, cement manufacture, cutting tools, for road aggregate, and roadstones. 


Economic:

Green schist also has its commercial uses. It can be used as blackboards, manufacturing of tools, and writing slates.





























































References:

https://rocks.comparenature.com/en/greenschist-uses/model-135-7

Metamorphic Rock Classification. (n.d.). Retrieved from http://faculty.chemeketa.edu/afrank1/rocks/metamorphic/metaclass.htm

Basac Formation. (n.d.). Retrieved from http://r7.mgb.gov.ph/?mdocs-file=6600

Greenschist Uses. Retrieved from https://rocks.comparenature.com/en/greenschist-uses/model-135-7








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