Mineral or Rock Project

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Montgomery County Community College *

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120

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Geology

Date

Apr 3, 2024

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docx

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8

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A Building Block Rock: Coquina Madeline Irwin & Liam Casey February 8, 2024 Introduction and Rationale Minerals and rocks provide a template of what changes have occurred over the span of Earth’s existence. Through many different scientific methods, the identification of different minerals and rocks has become a very common process. Identifying both minerals and rocks is extremely important as these identifications lead to an understanding of the composition, formation, and history of the Earth. Additionally, in an article entitled “Collecting Rocks”, Rachel Barker explains that “ By studying how rocks form and change, scientists have built a solid understanding of the Earth we live on and its long history” (Barker, 2022), which leads to the identification of rocks being extremely important in order to understand the history of the Earth. The sample being analyzed is pictured below in Figure 1. The source does not reveal where the sample originated from. ( Cronin-Geoscience-ed4828, 2020). Based purely on the physical appearance of this specimen (Figure 1), the conclusion that this specimen can be identified as coquina has been gathered. This conclusion has been formed by evaluating the initial appearance of this specimen, which showed a large amount of shell fragments being loosely cemented. Aside from the shells, this specimen appears to be a tan color. The specimen feels very porous with almost a  granular texture. Based on the initial observations and an article entitled “The Impact of Coquina: Unlocking the Mystery Behind the Endurance of the Oldest Fort in the United States” which explains, “ Coquina is primarily made up of crushed shell,
fragmented fossils and coral, limestone, sand, minerals and clay [ 1 ].” (Subhash, et al., 2015), the observations of this specimen (Figure 1) appear to be coquina. Figure 1 . Unknown Specimen. This image clearly shows the unknown specimen. Visibly showing the makeup of shells throughout the specimen and the material surrounding them. Methodology Proceeding to identify this rock sample, multiple tests were performed. Based on the findings of texture and composition of the sample, the conclusion of what type of rock this sample (Figure 1) is, was formed. Using Figure 3.16 in the textbook, the name of this rock was discovered (Tarbuck & Lutgens, 2017). Further, testing the specimen’s reaction to hydrochloric acid the mineral group of this rock was discovered. Alternatively, the specimen’s grinded reaction to hydrochloric acid was also tested ( Cronin-Geoscience-ed4828, 2020). Additionally, observing the grain size that the fossils are cemented in by taking a closer look at the specimen, the grain size was found (Figure 2). Knowing the composition, texture, reaction to hydrochloric acid, and the layers, I once again referred to Figure 3.16 in the textbook, and the rock’s name was then identified.
Figure 2. Closer view of a section of the rock sample shown in Figure 1. Data Analyses and Results By first analyzing the texture and composition of the unknown specimen, the conclusion that this specimen (Figure 1) is a sedimentary rock was formed. The original source of this specimen revealed that the composition consists of calcite and biochemical limestone ( Cronin- Geoscience-ed4828, 2020). I further analyzed the texture by examining the images (Figure 2) closely and observing the shell fragments throughout the specimen that were being loosely cemented. Further, matching my texture and composition findings with the “Chemical, biochemical, and organic sedimentary rocks” graph in the textbook (Figure 3.17), I was able to conclude that this specimen (Figure 1) is sedimentary (Tarbuck & Lutgens, 2017). The matrix of this specimen (Figure 2) is fine-grained and consists of sediments that are silt or clay-sized particles that hold the fossils together ( Cronin-Geoscience-ed4828, 2020). Further identification, such as the cleavage and streak color, of this specimen is unclear. Although the specimen’s primary minerals reacted weakly to hydrochloric acid, with grinding of the specimen the reaction
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