Author Question: You are given two rock samples; one is said to be a clastic sedimentary rock and the other a ... (Read 75 times)

krzymel · **on:** Jul 16, 2018

You are given two rock samples; one is said to be a clastic sedimentary rock and the other a chemical sedimentary rock. How can you tell which is which?

What will be an ideal response?

Question 2

Using the principle of Uniformitarianism, what can you infer about sandstone found on a beach?

What will be an ideal response?

katieost · **Reply #1 on:** Jul 16, 2018

Answer to Question 1

Answer: Chemical sedimentary rocks are formed when ions dissolve in water by chemical weathering, and later precipitate as new mineral crystals. The minerals that precipitate from water are those whose chemical constituents most readily dissolve in water. Chemical sedimentary rocks are, therefore, most commonly composed of minerals such as calcite, dolomite, gypsum, and halite, which are strongly ionic and easily dissolve in water. So, the sample with these minerals is most likely the chemical sedimentary rock. Clastic sediment consists of loose particles generated by weathering and then transported to a final site of deposition by flowing water, blowing wind, or sliding glaciers. This loose sediment does not become rock until it undergoes compaction under the weight of additional accumulating sediment and, especially, until the precipitation of cementing minerals between grains consolidates it into sedimentary rock.

Answer to Question 2

Answer: The grains in the stone resemble the loose grains of quartz (sand) that cover the beach. So, it makes sense that these grains were formed in the same manner as the sand (processes of weathering) but then cemented together somehow. When closer examining the stone, a white film is seen between the grains, as if it was holding the grains together. It resembles calcite, and to test this idea, dilute acid is applied to the rock and the film fizzes and dissolves, suggesting it is in fact calcite.