Lab 2:

Rock Identification:

There are seven igneous rocks, three sedimentary, and two metamorphic rocks to identify in this evening's lab. Your first mission is to determine whether your rocks are igneous, sedimentary, or metamorphic. Be sure to refer to both your textbook and lab book for the definitions of these three rock types. Additionally, seven mineral specimens (samples 1 to 8) that are common in these rocks are included (do not identify these as rocks!). Your mission is to fill out tables 2.2, 2.4, and 2.6 in your book that will result in the identification of the ten rocks to be included in your kit. Additionally, answer the below questions that will help you in identification of your rocks.

Igneous Rocks:

1. How many igneous rocks have a fine-grained texture? A coarse-grained texture?

2. What does the texture of an igneous rock indicate about the location in which it was crystallized from molten rock material?

3. One of your igneous rocks while appearing to be coarse-grained actually has a glassy texture. Where did this glass solidify, deep below the surface or on the surface?

4. Does the glassy igneous rock have mineral crystals?

5. Of the igneous rocks that have visible mineral grains determine the specimens that are dominated by ferromagnesium minerals? By non-ferromagnesium minerals?

6. Igneous rocks with a fine-grained texture are particularly difficult to identify. If you can not easily identify the minerals in these rocks then what physical property can be used to differentiate different fine-grained rocks?

7. Identify the common minerals that are present in your coarse-grained igneous rocks? List each rock and the minerals in that rock.

8. Chemically, igneous rocks can be subdivided based on their chemistry (SiO₂ content) into ultramafic, mafic, intermediate, and felsic. When you are completed with the identification of your rocks (except the rock with a glassy texture) indicate the chemical category of each of your identified igneous rocks.

9. If you where to drill 15 km down below Laredo you would likely encounter crystalline bedrock. What type of igneous rock would we most likely encounter in this situation? (LOOK AT pg. 178 IN TEXTBOOK)

10. If you where to drill 5 km down below the bottom of the sea floor in the middle of the Atlantic ocean what type of igneous rock would you encounter?

11. Still out in the middle of the Atlantic Ocean. But this time the drill stem breaks after only 1 km. You pull up rocks from that depth? What type of igneous rock are you likely to find.

12. What igneous rock type that makes up the mantle? Hint: we do not currently have specimens of this rock type in your kit.

13. Compare the eruptive nature (gentle vs. violent) for the volcanic rocks you identified in table 2.2.

14. Compare the chemistry of a gabbro and granite. Specifically, which of these rocks is most likely to have abundant Na, Al, and K in it!

Sedimentary Rocks:

15. You have one detrital sedimentary rock and two chemical sedimentary rocks. List the type of sedimentary rocks for each of your specimens. Detrital sedimentary rocks consist of mineral grains derived from the break-down of pre-existing rocks. Chemical sedimentary rocks are either chemically precipitated from water or consist of biologically produced grains of material.

16. Your detrital rock consists of what sized material? Coarse-sized = pebbles to boulders; Medium-sized = sand; Fine-sized < can only see grains with a microscope.

17. Name an environment where the sediment that makes up your detrital rock could have been deposited?

18. Your detrital rock consists of mostly what mineral included in your kit (no not potassium feldspar, the pink mineral).

19. Note that the red color in your detrital rock is derived from hematite that finely coats the individual grains that make up this rock. Do you think that this coating may be responsible for the transformation of loose sediment into a detrital sedimentary rock. Elaborate!

20. What types of biological materials are present in the two chemical sedimentary rocks in your kit?

21. One of these rocks actually is not made up of minerals? What is it and why is it not a mineral? (Refer to your notes on the precise definition of a mineral)

Metamorphic Rocks:

Metamorphic rocks form at high temperatures and pressures in the earth that change one rock type into another rock.

22. What types of texture do your metamorphic rocks have? Be sure to list the rocks and the textures (foliated vs. non-foliated) that they exhibit.

23. Identify the minerals present in your metamorphic rocks. Again list the rocks and the minerals that are present in each of your metamorphic rocks.

24. Discuss the protoliths of your metamorphic rocks.