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GEOL 101 - Physical Geology Laboratory

METAMORPHIC ROCKS PRELAB #6

PRELAB SECTION – To be completed before labs starts:

I. Introduction & Purpose:

The purpose of this laboratory exercise is to become familiar with identifying common metamorphic rocks and understanding their depositional origin. In this lab you will learn to identify metamorphic rocks in hand samples from their physical properties. You will become familiar with the most common metamorphic rock-forming minerals and processes. The nature and origin of metamorphic rocks, the major types of metamorphic rocks, and their structures, and the connection between plate tectonics and metamorphic rocks in the rock cycle will be explored.

II. General Overview and Classification of Metamorphic Rocks

A. Defining Metamorphism:

Directions: Answer the following (from lecture and lab text: see page 133):

1) Define "metamorphism" _________________________________________________

2) Every metamorphic rock has a _________________ rock (or protolith) - the original rock

type that was metamorphosed into the resultant metamorphic rock, i.e. the source rock.

B. Conditions of Metamorphism:

Metamorphic rocks form as a result of changing crustal conditions, e.g. increasing pressures and/or

temperatures, that are between that of igneous and sedimentary rock-forming environments.

1). The four major agents of change that cause rocks to metamorphose (see page 133):

a) _____________ , b) _____________ , c) _____________ , and/or d) ______________

C. Processes of Metamorphism:

Metamorphic processes that are forming the metamorphic rocks occur at various scales within the

Earth, and the type of internal earth agents involved is used to define the type of metamorphism.

One type is related to magmatism, and the other type is related to faulting and mountain building.

1) The two major types of metamorphism that are agent-dependent (page 134):

a) ________________________ , and b) ________________________

2) Question: Very briefly describe the differences between these two types of metamorphism:

____________________________________________________________________________________________________________________

D. Classification and Identification of Metamorphic Rocks

1) Classification and identification of metamorphic rocks are based upon two major physical criteria:

a) ______________________ , and b) _______________________

2) Metamorphic rocks are divided into two major groups based on whether the rock has a layered

versus non-layered texture. See Figure 7.4, page 136. Special alternative names for these are:

a) Layered = ___________________ and b) Non-layered = ___________________

E. Foliated Metamorphic Rocks

1) Metamorphic rocks that possess a foliated and/or layered fabric have a crystalline texture

consisting of elongate and/or platy crystals that all share a preferred orientation within the rock.

Metamorphic rock s that have foliated/layered fabrics originate in two types of metamorphic

environments: Regional Metamorphism (RM) and Dynamic Metamorphism (DM).

2) There are four common types of metamorphic rock s that have foliated-layered textures. Each

foliation type is unique and represents a progressive increasing scale of intensity of regional

metamorphism as go from slate to gneiss. The textural character of foliated and/or layered

metamorphic rock can vary greatly as a function of 1) grain size, 2) degree of preferred

orientation of the rock's mineral crystals, and 3) degree of layered segregation of light minerals

from dark minerals.

3) The foliated/layered metamorphic rocks are classified primarily upon texture, with mineralogy

a secondary criteria. There are four visually distinctive types of foliated rocks (listed below).

Directions: Describe the texture and mineralogy of the four foliated rock types (see Figure 7.15)

Rock Name Textural Features Rock Mineralogy

1. Slate _______________________________________ ________________________

2. Phyllite ______________________________________ ________________________

3. Schist _______________________________________ ________________________

4. Gneiss _______________________________________ ________________________

Please note that there are infinite shades of gray between these four types – no sharp divisions

F. Non-Foliated-Non-Layered Metamorphic Rocks

1) Metamorphic rocks that have non-foliated (non-layered) textures originate in two types of

metamorphic environments: regional metamorphism (RM) and contact metamorphism (CM).

Note that the nonfoliated metamorphic rocks that form by regional metamorphism RM are mostly

mono-mineralic (mostly of one mineral type), having mineral crystals that are neither platy nor

tabular, such as quartz and calcite. Note that amphibolite and serpentinite may exhibit foliation.

2) As noted above, the non-foliated (non-layered) metamorphic rocks consist of equant shaped

mineral crystals that have no preferred orientation or arrangement. These rocks have a massive,

homogenous "crystalline" texture, much like that of either, phaneritic granite, or aphanitic basalt.

The non-foliated metamorphic rocks are classified primarily upon mineral composition.

3) There are four common types of metamorphic rock s that have non-foliated/ non-layered fabrics:

Directions: Describe the texture and mineralogy of the four non-foliated rock types (see Fig. 7.15)

Rock Name Textural Features Rock Mineralogy

1. Quartzite _______________________________________ ________________________

2. Marble _______________________________________ ________________________

3. Amphibolite ____________________________________ ________________________

4. Serpentinite ____________________________________ ________________________

METAMORPHIC ROCKS IDENTIFICATION - IN-LAB SECTION

I. Preliminary Examination of the Metamorphic Rock Types:

A. Introduction: The instructor has assembled 2 reference collections of metamorphic rocks for

you to become familiarized with the two major types of metamorphic rocks: foliated and nonfoliated.

Directions: Carefully study each rock’s: 1) physical characteristics, including texture and

composition, and 2) metamorphic origin: the rock’s metamorphic environment and parent rock.

Make observational notes of the samples. Discuss your observations with your group.

II. Foliated-Non-Layered Metamorphic Rocks

A. Exercise 1 - Sample Group “X” has representative hand samples of each of the foliated rock

types. Study each sample carefully and make some brief descriptions of the rock's character

(texture, foliated fabric & minerals). Carefully study pages 137-139 for reference.

Observational Notes

Sample #s X1 and X2 = Slate _____________________________________________________

Sample #s X3 and X4 =Phyllite _____________________________________________________

Sample #s X5, and X6 = Schist _____________________________________________________

Sample #s X7 and X8 = Gneiss ____________________________________________________

B. Exercise 2 – Compare and contrast the foliated metamorphic rocks in Sample Collection “X”.

Question: How does slate differ from both phyllite and schist?

Question: How does gneiss differ from the other three foliated rocks?

Question: What are the main criteria you use to distinguish between these four rock types?

III. Non-Foliated-Non-Layered Metamorphic Rocks

A. Exercise 1 - Sample Collection “Y” has representative hand samples of the nonfoliated rock

types. For each hand sample, briefly describe the rock's character (texture, fabric, minerals)

Observational Notes

Sample #s Y1 = Quartzite ____________________________________________________

Sample #s Y2 = Marble ______________________________________________________

Sample #s Y3 = Amphibolite __________________________________________________

Sample #s Y4 = Serpentinite _________________________________________________

B. Exercise 2 – Compare and contrast nonfoliated metamorphic rocks in Sample Collection “Y”.

Question: How does quartzite differ from marble? How are they similar?

Question: How does amphibolite differ from serpentinite? How are they similar?

Question: What are the main criteria you use to distinguish between these four rock types?

IV. Procedure for Describing and Identifying Metamorphic Rocks:

A 4-Step chart for the analysis and classification of metamorphic rocks is found in Figure 2.33

on page 32 . Use this chart, and the additional directions found on page 32 to help you learn to

identify metamorphic rocks both, in hand sample and in the field.

A. Four-step Identification Procedure - A brief description of the 4 determinant steps:

Step 1: Texture = a) Foliated or Non-Foliated? AND b) Coarse-, medium-, or fine-grained?

Step 2: Rock Composition = Identifiable Minerals?

Step 3: Name the Rock.

Step 4: Name the Most Likely Parent Rock.

V. Identifying 9 Unknown Metamorphic Hand Samples

Instructions: Sample Collection “Z” has nine unknown metamorphic rock samples. Using the

4-step procedure outlined above, complete the worksheet chart below for all eight unknown samples.

Be sure to Circle only the appropriate texture and mineralogy. List rock name and parent rock.

Unknown Metamorphic Rock Hand Samples Worksheet – Collection “Z”

Sample# Z1

a) Texture: Foliated or Non-foliated? AND Fine-Grained. or Medium-Gr. or Coarse-Gr.?