Question

Part 1. Getting to know your sedimentary rocks (40-50 min)

The lecture notes covered some basics of the textures and mineralogy used to name sedimentary rocks as well as information concerning the formation and transportation of sediments. In addition to this information you will also need the following to complete this part of the lab:

Mineral and rock set (plus the accompanying booklet for reference)

Rock and Mineral ID charts

Any other notes or textbook you want for reference

Couple of drops of vinegar

Mineral 19. Sandstone (although more appropriately referred to as Quartz Sandstone) and Mineral 21. Arkose

1. Both of these sedimentary rocks consist of sand sized grains cemented together. What is the major difference between them?

2. Given the difference noted in Q1, and your knowledge of chemical and mechanical weathering (refer to notes and textbook as needed), which of these two rocks had sediments that underwent a higher degree of weathering and transportation prior to lithification? Explain your reasoning.

Mineral 20. Shale

3. The sediment size in shales is {very large, large, medium, small, very small}. Choose one.

4. Given this grain size, and what you know about sediment transportation, what would the relative velocity of the water that deposited these sediments? (I don’t need an actual speed, just a general fast/slow/medium/etc.)        

5. Give an example sedimentary environment/location where the sediment that makes up this shale could have been deposited (refer to the textbook if you need some help with sedimentary environment examples).

Mineral 22. Conglomerate and Mineral 23. Breccia

6. Both of these sedimentary rocks can have the same wide range of clast size. What is the main difference between a conglomerate and a breccia? I.e. in looking at them both, how would you identify one vs. the other?

7. Given your answer in the question above, what does this imply about how far the sediments had travelled prior to being cemented into these rocks? Explain your reasoning. (hint: read about transportation and rounding in the textbook)

Mineral 24. Limestone (depending on your specific sample, this may or may not contain fossils)

8. Unlike the other sedimentary rocks in this rock set, this limestone is not a clastic sedimentary rock. What type of sedimentary rock is it?

9. What mineral is limestone composed of?

10. Because of the mineral composition of limestone, if you were to place a couple of drops of acid (HCl) on the limestone what should happen? (it may help you to refer to the mineral ID chart)

Answer 1

1. Quartz Sandstone means rich in quartz. Quartz rich sandstone are actually called as Quartz arenites. So major difference in between them is that the Arkose is generally very rich in Feldspar but Quartz Sandstone is not. Quartz Sandstone have a high extent of transport but arkose is less. Maturity of the Quartz Sandstone is very good in terms of composition as well as Texture but same is immature for the Arkose. Sorting in quartz Sandstone is very well snorted but Arkose is poorly sorted.

2. Extent of transportation is more in quartz Sandstone than Arkose because of same aforesaid reason.

3. Shale consist of mud and clay and silt so it has very small grain size approximately less than 0.063mm.

4. Due to its fine grain size a very low velocity or stagnant water condition is needed for formation of shale.

5. Shale can be deposited in deep marine condition, fluvial and in lacustrain environment where the above condition is prominent. Because shale generally occur in lamination which have thickness less than 1 cm.

6. Actually conglomerate is rounded and Breccia is an angular rock. Conglomerate are form in Alluvial environment but Breccia are form in multi environmental conditions.

7. Because of angular nature of the Breccia it represent a very low extent of transportation same is high in case of Conglomerate.

8. Limestone is a non clastic sedimentary rock because it form due to precipitation of The Mineral CaCO₃ Calcite.

9. Calcite

10. When we put some HCl in limestone it reacts and gives rise to CO₂ Gas Carbon dioxide. This is called acid test of limestone.