METAMORPHIC ROCKS

Metamorphism is the process by which a rock undergoes changes in texture and mineralogy in
the solid state at temperatures below its melting point. The resulting rock is a product of many
variables including the composition of the parent rock, temperature, pressure, presence of
chemically reactive fluids, and presence or absence of deforming stresses. The many variations
make these rocks the most difficult of the three basic rock types to completely understand.
Important changes that may take place during metamorphism include:
 Recrystallization of existing minerals, especially into larger crystals;
 Mineralogical Change as of new minerals develop some of the old ones disappear; and
 Foliation – Reorientation of existing mineral crystals and growth of new ones in parallel or
     nearly parallel planes.
If the protolith is composed mostly of a single mineral, and chemically reactive fluids are absent,
metamorphic changes take place by recrystallization alone. For example, the quartz grains in a
quartz sandstone reform into interlocking quartz crystal, producing the metamorphic rock
quartzite. Limestone behaves in a similar fashion, with the calcite particles crystallizing,
producing the metamorphic rock marble. If, on the other hand, the protolith contains chemically
complex minerals such as the clay minerals, metamorphic reactions produce new mineral species
through recombination of elements derived from the clay. Often, these new minerals are identical
to, or similar to, the silicate minerals that originally decomposed into the clay minerals. In
addition, directed stresses from regional metamorphism acting on chemically complex rocks will
result in foliation.

Part 1 – Nonfoliated Metamorphic Rocks And Their Sedimentary Parent Rocks

    1. Find the samples of quartz sandstone and limestone from the sedimentary box. These are
       the parent rocks for the two non-foliated metamorphic rocks Write the name and sample
       number in the right hand column, below.

    2. Examine the metamorphic samples. You are looking for the non-foliated metamorphic
       rocks, which means no layering or mineral separation. There are two. One of the
       specimens is quartzite, the other marble. They look alike. One of them has a parent rock
       of limestone, the other has a parent rock of quartz sandstone. What test will help you to
       determine which metamorphic rock is marble and which is limestone?

    3. How does the texture of the marble differ from that of the limestone? How does the
       texture of the quartzite differ from that of the sandstone?

    4. Complete the table.
Metamorphic Rock Name Major Mineral                    Sedimentary parent
and Sample Number                                      sample number
                                                       Sandstone #

                                                       Limestone #

Part 2 – Foliated Metamorphic Rocks and the Sedimentary parent rock, shale

    5. Identify the sedimentary rock shale from the sedimentary collection. Sample Number of
       Shale: ________

    6. Slate is the first foliated metamorphic rock to form from shale. Identify the slate from
       the metamorphic collection. Fill in the information in the table below, with slate in the 1st

    7. Compare the slate with its parent rock shale. What features of the slate distinguish it from
       the shale?

Review the section in your text entitled Foliated Texture. Using this information, along with the
accompanying figures, list them in order of increasing metamorphic grade. Chlorite is a mineral
from the mica family that forms under metamorphic conditions. It is often found in Phyllites.
Garnet, another metamorphic mineral, is a maroon to brown colored mineral with a glassy luster.
Some of our schists contain mica.

Metamorphic Rock Name and           Minerals present                 Type of Foliation


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