Please reply to both POST1 and POST2 with at least 250 words

POST1:

For this week’s discussion post, I chose to write about limestone. Limestone is considered an organic sedimentary type of rock, which is formed through the solidification of sediment. “Sediment is a naturally occurring material that is broken down by the processes of weathering and erosion and is subsequently naturally transported” (Micu, 2019). These types of rocks also form by the overturning of the Earth’s material, such as the surface or bodies of water.

Limestone is composed primarily of calcium carbonate in the form of a mineral called calcite. This mineral can be one of three materials: organic, chemical, or detrital in origin. It forms in shallow, calm, warm marine waters where organisms are able to form calcium carbonate shells and skeletons. For example, when an animal dies, their shell or skeletal debris accumulate as a sediment that might be lithified into limestone and form into this type of sediment. Most limestone can be found in areas between 30 degrees north latitude and 30 degrees south latitude in areas like the Caribbean Sea, Gulf of Mexico, and around the Pacific Ocean Islands. Limestone can also be formed as chemical sedimentary rocks by direct precipitation of calcium carbonate from marine or fresh water. Although these are thought to be less abundant than biological limestone.

Limestone is known for its large amounts of marine animal fossil content that settled on the ocean floor over millions of years. Overtime, they were compacted, creating limestone from the sediments and pressure of the ocean floor. This tells us there was sitting water for years and years where limestone is found today. An interesting fact about limestone in the area I live (San Antonino, Texas):

– San Antonio straddles the Balcones Fault.
– A limestone quarry was built on the Balcones Fault, but has been reconstructed as the Sunken Garden Theater which now holds concerts and plays.
– Since I live on limestone, I can only plant certain trees and plants since the limestone is only a few inches below the dirt (we also have no basements!).
– I live and work within a mile of our local quarry and every Friday afternoon they blast the limestone to create crushed stone. My entire building shakes and is quite scary when you don’t know what is going on!

Resources:
Limestone. (n.d.). Retrieved from https://geology.com/rocks/limestone.shtml#:~:targe… of Limestone, siderite, and other minerals.

Micu, A. (2019, April 24). The types of rock: igneous, metamorphic and sedimentary. Retrieved from https://www.zmescience.com/other/science-abc/types-of-rock/.

Nerc. (n.d.). How is limestone formed? Retrieved from https://www.bgs.ac.uk/discoveringGeology/geologyOfBritain/limestoneLandscapes/whatIsLimestone/howFormed.html.

POST2:

The rock of my choosing the Obsidian a natural igneous rock, volcanic glass, black in color with a smooth texture or what may appear to be shiny with a glassy, streak finish. Obsidian is absent from minerals due to the crystalline process within the rock. The chemical process to form this rock is formed through the geologic process of lava flow that is initiated underground when the mantle pressure and heat intensifies, the rock will melt to form magma that will rise up through the crust of the surface and initiate the lava flow. Obsidian forms at the end of the volcano cycle. The chemical composition includes about 70% of silicon dioxide that is formed through rapid cooling from volcano lava. Changes in the magma water content can impact how streaks show up in the rock. The last Obsidian flow occurred over 1300 years ago at Newberry volcano.

Obsidian artifacts turn up at archaeological sites going back at least as far as 1.7 million years ago, when an early member of the genus Homo made tools with it at the Ethiopian site of Melka Kunture. Tarkach (2019). Because the rock is hard and brittle Obsidian was useful in the Stone Age for tools such as spears, scalpels for surgery and even jewelry. Discovered by Native Americans it has made it’s way across the country Obsidian is found in Argentina, Canada, Chile Greece, Italy and United States in Oregon as a popular location to name a few.

Obsidian can also be found in reddish brownish colors as a result of the microscopic crystals and flow layers of the lava. A interesting fact is obsidian it played a role in HBO’s hit Game of Thrones and while I never knew this, it has made me want to go back and look at the series.

References

Andrei, Mihai. (2015) the types of rock, igneous, metamorphic an sedimentary, retrieved from https://www.zmescience.com/other/science-abc/types-of-rock/ (Links to an external site.)

TARLACH, GEMMA. Discover. Jun2019, Vol. 40 Issue 5, p26-30. 3p. 7 Color Photographs. , Database: Academic Search Premier (Links to an external site.)

Johnson, C., Affolter, M., Inkenbrandt, P., & Mosher, C., Salt Lake Community College. (2017). An introduction to geology. Retrieved from http://opengeology.org/textbook/