METAMORPHIC ROCKS LAB

PROBLEM: How can you identify metamorphic rocks?

HYPOTHESIS:

MATERIALS: Earth Science - Metamorphic Rocks, Swift GH microscope or Hand Lens 

Part I: General Questions Answer each of the following questions.

1. Can metamorphic rocks form on the Earth’s surface? Explain your answer.

2. In what areas of the Earth is contact metamorphism likely to occur?

3. Where might regional metamorphism take place?

Part II Examining Metamorphic Rocks and Minerals Look at each of the metamorphic rock specimens. Carefully answer the questions for each.

Muscovite and biotite are both flat silicate minerals. This is because the silica compounds they contain are joined together to make sheets, like the pages of a book. Mica commonly forms under metamorphic conditions. However, you find mica in igneous and sedimentary rocks.

A. What properties does mica have that could associate it with metamorphic rocks?

B. What is the difference between the two micas?

C. How can you recognize mica in rocks?

Garnets are most common in metamorphic rocks formed under moderate temperature and pressure. It comes in various colors ranging from red to green. It forms a characteristic 12 sided crystal.

A. Describe your crystal.

B. Can a steel nail scratch your specimen?

Mica schist is a common metamorphic rock that is produced by regional metamorphism. The shiny look of schist is one of its key characteristics. The schist also has a nicely developed foliation. The word foliation comes from the Latin "folia" meaning leaves.

A. In what way does schist have a "leaf-like" appearance?

B. Are the minerals present in this schist visible with the naked eye?

C. What is the sparkly mineral visible in this schist?

4. MARBLE is metamorphosed limestone. Limestone is a sedimentary rock that is mainly composed of calcite, derived from the shells of living organisms like clams and snails. Marble can be produced by contact or regional metamorphism. Marble does not develop foliation like schist, because the calcite crystals are all about the same size. There is no way for them to line up. Marbles often contain other minerals, such as quartz, mica, and hematite.

A. Is this sample of marble fine (small) or coarse (large) grained?

B. What happens when dilute HCl is dropped on marble? Why?

C. How many types of minerals are in this specimen of marble?

Quartzite is a very hard metamorphic rock. It can be made by contact or regional metamorphism. Like marble, it is made of crystals that are all about the same size, so it does not have foliation. Primitive people often used quartzite to make bladed weapons like knives and arrowheads.

A. From its name, what mineral makes up quartzite?

B. Can you tell this just by looking at the rock? Explain your answer.

C. Which would be more useful in identifying quartzite, a bottle of HCL or a steel knife? Explain your answer

D. What was the likely mineral composition of the rock from which quartzite was made?

E. You saw a rock in the sedimentary lab that could be this original rock. Can you guess which one it is?

Slate is formed by regional metamorphism. It is a low-grade metamorphic rock, meaning that it was created by relatively low temperature and pressure. Schist, which you have already examined, is a medium-grade metamorphic rock.

A. Describe your piece of slate.

B. Slate is formed under low to moderate pressure and temperature conditions. Does slate ring when lightly dropped?

C. Can you think of any uses for a large piece of slate? (Hint: think about buildings.)

D. Which sedimentary rock was slate most likely made from?

Gneiss is a high-grade metamorphic rock. It is common only in areas of regional metamorphism. Several different rocks, such as granite, schist, and diorite can be metamorphosed to make gneiss. This is one of the most difficult things to understand about metamorphic rocks. Different preexisting rocks can produce the same kind of metamorphic rock.

A. Describe your piece of gneiss. Make sure you look at the arrangement of the minerals.

B. Is gneiss banded or layered?

C. What makes up the different bands?

8. SERPENTINITE

Serpentinite is a metamorphic rock produced largely by metamorphism along fault zones. The original rock is often an igneous rock like gabbro or basalt. Serpentinite is composed mainly of the mineral serpentine. Serpentinite is the state rock of California. However, the state legislators didn't know the difference between serpentinite (the rock) and serpentine (the mineral), and voted to make "serpentine" the state rock.

A. Where do you think serpentinite got its name?

B. How does serpentinite "feel?"

C. Can you think of any uses for serpentinite?

Hornfel is a fine grained metamorphic rock that is nonfoliated. It usually forms under low pressure and varying ranges of temperature. It is difficult to distinguish.

A. What igneous rock could you confuse hornfels with?

B. Describe your sample.

10. PHYLLITE

Phyllite is a metamorphic rock that has not been under as much pressure as slate. It is usually derived from mudstone or shale.

1. Describe your specimen?

2. What is the difference of dropping phyllite about 6 cm from a hard surface and a piece of slate?